Christian Kerbiriou

Romain Julliard

Demographic consequences of prey availability and diet of Red-billed Choughs Pyrrhocorax pyrrhocorax

Keywords: Pyrrhocorax pyrrhocorax, chough diet, prey availability, monthly survival, fledging success, capture-mark-recapture

Capsule Variation in prey availability appears to influence Chough fledging success and juvenile survival. Aims To determine seasonal and annual variations in Chough prey and how these influence fledging success and juvenile survival. Methods Chough faeces (n = 437, 3905 invertebrates) were collected year-round and analysed to determine diet composition. Seasonal and annual variation in prey abundance in Chough foraging habitat was assessed using pitfall trapping (n = 747, 27 124 invertebrates) between 1996 and 2003. Fledging success was estimated for a population of 12 breeding pairs; juvenile survival was estimated by year-round resighting (n < 2500) of individual birds that were colour-ringed as nestlings.

Results

From April to June a high biomass of prey and a great variety of species were observed. Between July and October, both biomass and species diversity were reduced; prey consisted mainly of ants and a few beetle species. From November to March, biomass availability was intermediate, with the diet consisting mostly of Tipulidae larvae, plants and dung beetles. Chough juvenile monthly survival was low in August, November and December. Annual variation in fledging success was correlated with prey biomass availability in May.

Conclusion Seasonal variation in the availability of prey species and their biomass influences

Chough demography.

INTRODUCTION

The most frequently reported threat to European bird species is habitat change resulting from the intensification of agricultural practices [START_REF] Benton | Farmland biodiversity : is habitat heterogeneity the key?[END_REF][START_REF] Krebs | The second silent spring?[END_REF][START_REF] Pain | Farming and birds in Europe[END_REF][START_REF] Shrubb | The Kestrel[END_REF][START_REF] Stoate | Ecological impacts of arable intensification in Europe[END_REF][START_REF] Tucker | Effects of agricultural practices on filed use by invertebrate-feeding birds in winter[END_REF][START_REF] Tucker | Birds in Europe their conservation status[END_REF].

However, agricultural abandonment can also result in declines in farmland bird populations [START_REF] Bignal | Transhumance in Spain[END_REF]. This may be particularly true for Red-billed Choughs Pyrrhocorax pyrrhocorax, a species closely associated with low-intensity agricultural habitats such as grazed rough grass and permanent pastures [START_REF] Warnes | A study of the ecology of the Chough Pyrrhocorax pyrrhocorax L. on the isle of Islay[END_REF][START_REF] Mccracken | An assessment of chough Pyrrhocorax pyrrhocorax diet using multivariate analysis technique[END_REF][START_REF] Rolando | The foraging behaviour of the chough Pyrrhocorax pyrrhocorax in two contrasting habitats[END_REF][START_REF] Bignal | Feeding behavior of nestling choughs in the Scottish Hebrides[END_REF][START_REF] Madders | Distribution and foraging habitat preferences of Choughs on the Oa peninsula, Islay[END_REF][START_REF] Robertson | Habitat selection and foraging behavior of breeding choughs Pyrrhocorax pyrrhocorax L. in county Donegal[END_REF][START_REF] Blanco | Traditional farming and key foraging habitats for chough Pyrrhocorax pyrrhocorax conservation in a Spanish pseudosteppe landscape[END_REF].

Intensification and abandonment of agricultural practices have been suggested as important factors leading to declines in Chough populations and their eventual extinction in parts of western Europe in the second half of the 20th century [START_REF] Rolfe | Status of the Chough in Scotland[END_REF][START_REF] Garcia-Dory | Datos sobre la ecologia del genero Pyrrhocorax (P. pyrrhocorax y P. graculus) en el parque Nacional de la Montana de Covodonga[END_REF][START_REF] Kerbiriou | Originalité de la population bretonne de crave à bec rouge dans un contexte européen[END_REF][START_REF] Mccracken | An assessment of chough Pyrrhocorax pyrrhocorax diet using multivariate analysis technique[END_REF][START_REF] Meyer | The diet of the chough Pyrrhocorax pyrrhocorax as indicated by analysis of digested prey remains[END_REF][START_REF] Dendaletche | Alpine Chough and Choughs : biological integrators of agropastoralism ecosystems in the Pyrenees[END_REF][START_REF] Blanco | Traditional farming and key foraging habitats for chough Pyrrhocorax pyrrhocorax conservation in a Spanish pseudosteppe landscape[END_REF]. At the local scale, conservation managers are often confronted with a decrease in grazing pressure and an increase in abandoned land [START_REF] Ravayrol | Le crave à bec rouge sur le Larzac méridional[END_REF][START_REF] Kerbiriou | Landscape management for the Chough, Porz Gwenn (Isle of Ouessant, France) in Chough and Farming Seminar[END_REF][START_REF] Webber | A niche scheme tackling the decline of traditional management on Pembrokeshire's cliff-top and coastal slopes[END_REF][START_REF] Mccanch | The relationship between Red-Billed Chough Pyrrhocorax pyrrhocorax (L) breeding populations and grazing pressure on the Calf of Man[END_REF]. Several studies focusing on Chough diet have shown that these birds can use a great variety of surface-active insects; however, most studies outlined the importance of dung-associated insects, which appear to be one of the main components of Chough diet in spring, late summer and autumn [START_REF] Warnes | Habitat use and food of choughs on the island of Islay, Scotland. In: Chough and land-use in Europe[END_REF][START_REF] Mccracken | An assessment of chough Pyrrhocorax pyrrhocorax diet using multivariate analysis technique[END_REF][START_REF] Mccracken | Surface-active invertebrate communities and the availability of potential food for the Chough, Pyrrhocorax pyrrhocorax L., on pastures in north-west Islay[END_REF]. Some of these studies also pointed out the importance of cereals in the diet of Choughs, especially in autumn and winter [START_REF] Warnes | Habitat use and food of choughs on the island of Islay, Scotland. In: Chough and land-use in Europe[END_REF][START_REF] Mccracken | An assessment of chough Pyrrhocorax pyrrhocorax diet using multivariate analysis technique[END_REF]. Choughs are distributed from North Africa to central Asia. In western Europe, Chough populations are rare and exhibit a local and patchy distribution which appears to be related to a lack of suitable nesting sites (mainly cavities in cliffs) together with feeding areas characterized by open vegetation with low cover (Robert 1983[START_REF] Faringha | Medidas urgentes para a conservaçào da Gralda de bico vermelho Pyrrhocorax pyrrhocorax em Portugal[END_REF][START_REF] Rolando | The foraging behaviour of the chough Pyrrhocorax pyrrhocorax in two contrasting habitats[END_REF][START_REF] Bignal | Feeding behavior of nestling choughs in the Scottish Hebrides[END_REF][START_REF] Blanco | Traditional farming and key foraging habitats for chough Pyrrhocorax pyrrhocorax conservation in a Spanish pseudosteppe landscape[END_REF]. The small western French population of Choughs is now confined to a few sites in Brittany and appears to be one of the smallest and most isolated Chough populations of western Europe [START_REF] Tucker | Birds in Europe their conservation status[END_REF][START_REF] Kerbiriou | Originalité de la population bretonne de crave à bec rouge dans un contexte européen[END_REF]. This population decreased from probably 100-150 pairs in the 1960s to about 30 in the 1980s; presently it seems to have stabilized at 39-55 breeding pairs scattered in five population cores [START_REF] Kerbiriou | Recensement 2002 de la population bretonne de crave à bec rouge (Pyrrhocorax pyrrhocorax)[END_REF]. The Breton population of Choughs inhabit coastal cliffs and feed in cereal fields and sheep pastures on the coast. The increase in abandoned agricultural land in the 1960s has apparently led the remaining Chough population to use a greater proportion of natural habitats, such as maritime grassland and coastal heathland, which are probably similar to the habitats used before the emergence of agriculture.

We conducted a study on the seasonal and annual variation in prey availability in these Breton coastal habitats with the aim of identifying key prey types and determining how their abundance affects the Chough population.

METHODS

Study area

The study was conducted in Ouessant, a small island (1541 ha) located 20 km west of the western tip of Brittany, France (48 28′N, 5 5′W). Holding 13 breeding pairs, Ouessant appears to be one of the core populations of Brittany; the nearest population (four or five pairs) occurs on the mainland, 22 km away from the island. The number of breeding pairs on Ouessant has remained stable over the last 50 years but the total population size has decreased from about 80 individuals to 50 during that period. Humans exploited the whole island until the early 20th century, after which the population declined severely; this led to the complete disappearance of cultivated fields after 1970 and a progressive reduction in sheep grazing, from 4500 sheep in 1950 to 650 in 2000. As a result, pastures have been undergrazed and the area of abandoned agricultural land has increased, especially on the coastal strip. Today, abandoned agricultural lands, dominated by Bracken Pteridium aquilinum and Brambles Rubus fructicosus, cover more than half of the island [START_REF] Gourmelon | Historic land-use changes and implications for management of a small protected island[END_REF]. Extensive sheep grazing in central areas of the island is the only remnant of traditional agriculture [START_REF] Gourmelon | Historic land-use changes and implications for management of a small protected island[END_REF]). Currently, one-third of Ouessant is occupied by pasture dominated by Dactlylis glomerata, Holcus lanatus, Trifolium repens, and Lolium perenne; vegetation height ranges between 10 and 40 cm. In winter, sheep are free to wander and are sometimes seen grazing near the coastline. All remaining pastures appear undergrazed and unsuitable for Chough, as less than 1% of observations of feeding Choughs occur in this habitat [START_REF] Kerbiriou | Linking territory quality and reproductive success in the chough (Pyrrhocorax pyrrhocorax): implications for conservation management of an endangered population[END_REF]. Choughs feed essentially in coastal vegetation and especially in low coastal turf.

This vegetation, which grows on soil less than 15 cm thick, contains low plants (generally <5 cm high) and covers 62 ha, i.e. less than 5% of the total area of Ouessant. Low coastal turf is characterized by rocky outcrops and is dominated by Agrostis stolonifera maritima, Armeria maritima, Bromus ferroni, Catapodium loliaceum, Centaurium erythraea, Festuca rubra pruinosa, Isoetes histrix, Jasione montana, lichens (Cladonia sp.), Ophioglossum lusitanicum, Plantago coronopus, Sedum anglicum and Scilla verna. Most of these species have an early spring or even a winter cycle, i.e. they grow and (with the exception of perennial species) reproduce early and generally disappear during the dry period of summer. This vegetation is kept short by environmental constraints such as wind, sea spray, thin soil and human trampling [START_REF] Kerbiriou | Landscape management for the Chough, Porz Gwenn (Isle of Ouessant, France) in Chough and Farming Seminar[END_REF].

Data collection and statistical treatments

Faecal analysis

The majority of Chough faeces (359 samples) were collected from sites where birds were seen eating, while a small proportion were collected at night roosting sites (15 faecal samples in June) or close to nests, mainly during ringing operations (six samples in April, 38 in May and 19 in June). A total of 437 samples were analysed (Table 1), with most collected in 1996 and a small number (n = 59) collected in May each year between 1997 and 2001. Each faecal sample was moistened and examined with a binocular microscope (1.5-4 10 magnification). The animal, plant and mineral fractions were separated and identified. Using a reference collection of arthropods obtained by pitfall trapping in Chough foraging areas, the minimum number of individuals of each taxon present in each sample was estimated. Ants (Formicidae) were mainly identified from their heads, Coleoptera from their heads, mandibles, legs and elytra and Dermaptera from their cerci. Adult Diptera were identified from their wings, and larvae from posterior spiracles and mouthparts. The presence of adult Lepidoptera was detected by their wing scales. Spiders were identified from their head capsules and genitalia. Arthropod abundance in foraging habitats To assess monthly variations in arthropod prey availability in Chough feeding habitats, permanent pitfall traps were placed and checked every month: in 1996, ten traps were placed at each of six locations for 12 months (providing 683 usable samples). Pitfall trap sites were chosen according to the main Chough feeding areas. Subsequently, five traps were placed at one of the 1996 locations for ten months in 1997 (providing 44 usable samples), and from mid-April to mid-May in each of 1998, 2001, 2002 and 2003 (providing five usable samples each year). Field sampling was not performed in 1999 and 2000 due to lack of available time. All invertebrates collected were identified and counted (23 345 invertebrates in 1996; 2281, 321, 683, 948 and 867 in 1997, 1998, 2001, 2002 and 2003, respectively). A subsample (n > 30) of each invertebrate species caught was weighed (fresh weight) to allow an estimate to be made of the total biomass caught by pitfall in each habitat. Pitfall trapping is a widely used method to assess soil-surface activity of invertebrates [START_REF] Greenslade | Pitfall trapping as a method for studying population of Carabidae (Coleoptera)[END_REF][START_REF] Adis | Problems of interpreting arthropod sampling with pitfall traps[END_REF][START_REF] Luff | Some features influencing the efficiency of pitfall traps[END_REF]. The number of animals caught is known to depend both on invertebrate density and activity [START_REF] Mitchell | Ecology of two carabid beetles, Bembidion lampros and Trechus quadristriatus. Studies on populations of adults in the field, with special reference to the technique of pitfall trapping[END_REF][START_REF] Crawford | Spider arrival and primary establishment on a terrain depopulated by volcanic eruption at Mount St. Helens, Washington[END_REF] and thus does not yield completely accurate estimates of prey availability. However, it is a cheap and labour-saving method that offers a valuable means of monitoring soil-surface invertebrates [START_REF] Luff | Some features influencing the efficiency of pitfall traps[END_REF][START_REF] Boer | Fluctuations of density and survival of carabid population[END_REF]. Results from pitfall traps have been compared to exhaustive sampling on standardized squares to assess the accuracy of the pitfall trapping method. In the latter method, all invertebrates found in vegetation and in the first 2 cm of soil on a 50 50 cm square were collected manually and provided an accurate estimate of invertebrate density [START_REF] Canard | Essai d'étude écologique quantitative sur quelques groupes d'invertébrés épigés d'une lande sèche armoricaine[END_REF]). In the current study, similar sampling was conducted on five different squares each month between February and May 1997 (in April, only four squares were sampled) near the pitfall trap locations. Monthly variation in prey availability was analysed using analysis of variance.

Estimation of Chough demographic parameters

The gives the probability that the real model occurs among those considered for model selection [START_REF] Burnham | Model selection and inference, a practical information-theoretic approach[END_REF][START_REF] Lebreton | Modelling survival and testing biological hypothesis using marked animals: a unified approach with case studies[END_REF]. The variables used to model variation in juvenile resighting were month and year of birth. Because of the extremely high resighting rate, the disappearance date of any individual could be assessed to the nearest month (i.e.

individuals not recorded for more than 30 days were never seen again on the island). A similar colour-ringed programme was launched in the nearest mainland population to detect possible exchanges of individuals. Ouessant monthly juvenile survival was thus estimated using 'known fate' models implemented in the MARK program. Known fate data assume that there are no nuisance parameters involved in bird resightings and that the probability of encountering any living individual on each occasion (i.e. each month) is 1. June survival rate accounts for nest survival of old chicks during about 19 days (from ringing day, which occurred approximately three weeks after hatching, to fledging day). Fledging occurs around mid-June. Finally, we tested the correlation between interannual variation in prey availability and fledging success. Prey biomass records, collected at the same pitfall location in May 1996May , 1997May , 1998May , 2001May , 2002May and 2003, were correlated to the fledging success of the corresponding year using analysis of variance. The analysis also accounted for a possible effect of nest on fledging success; prey biomass effect was nested into the year effect.

RESULTS

Food types

The 437 faecal samples contained 3905 individual invertebrates. A total of 52 invertebrate prey species were identified. Plants were detected only in autumn and winter. The plant fraction was mainly wild grains (>90%) and some bulbs of Scilla verna; plants generally represented a negligible fraction of droppings, but could reach up to 57% in December (Table 1). The analysis of prey remains showed important seasonal variations ( 2).

Prey availability

Variation in invertebrate biomass, as assessed by pitfall trapping adjusted to month, appeared to be correlated with monthly invertebrate biomass as estimated via the exhaustive method (F1,14 = 5.59, P < 0.032, r2 = 0.84). All species known to occur in Chough faeces (Table 1), as well as any similar species collected in the pitfall traps, were considered as potential Chough prey; for example if only Drassodes cupreus remains were found in Chough faeces, all spider species of the genus Drassodes were considered as potential prey. Some species found in pitfall traps and not in faeces were not considered as prey; these were essentially very small species such as Acritus homeopathicus beetles (size <1 mm) or Liniphiidae spiders, or large species such as Megadontus purpurescens beetles. Prey availability in 1996 varied between months (F11,55 = 7.23, P < 0.0001) and significant variations were also detected across pitfall stations (F5,66 = 2.82, P = 0.02). On average, invertebrate prey biomass reached a maximum in spring and decreased to a low level in November and December; a similar pattern was observed in 1997 based on data drawn from a smaller sample (Fig. 3).

Key period for juvenile mortality

The monitoring of Chough reproduction phenology on Ouessant indicated that egg-laying occurred around mid-April and that juveniles fledged around mid-June (14 June ± 1 day, n = 73 nests). The juveniles were left to feed themselves mainly from late July/August onwards.

The analysis of juvenile resighting data focused on juvenile survival rates by month, to investigate whether there were any consistent key periods for juvenile mortality. Between November-December (survival rates = 0.81 and 0.69) (Fig. 4). Other months were characterized by high survival rates, ranging from 0.95 to 1.00 (Fig. 4). Fledging success varied across years, from 0.69 to 1.62 juveniles/pair with an average of 1.45 ± 0.13. The relationship between fledging success and prey availability in May 1996May , 1997May , 1998May , 2001May , 2002May and 2003 was analysed to determine whether there was any consistent relationship (Fig. 5). Yearly fledging success appeared to be influenced by nest-site (F16,5 = 4.92, P <0.0001) and fledging success adjusted to nest and year appeared to be influenced by variation in prey biomass (prey biomass effect nested to year effect F1,4 = 22.60, P = 0.009). No influence of major prey groups was detected on fledging success adjusted to nest (beetles: F1,4 = 0.49, P = 0.52; spiders: F1,4 = 2.18, P = 0.21; ants: F1,4 = 1.94, P = 0.24).

DISCUSSION

Diverse diet of Choughs on Ouessant

Some studies have found Red-billed Choughs to be almost exclusively insectivorous [START_REF] Matvejev | Le crave à bec rouge (Pyrrhocorax pyrrhocorax docilis GM.) en Yougoslavie[END_REF][START_REF] Rolfe | Status of the Chough in Scotland[END_REF][START_REF] Meyer | Observations on two Red-Billed Choughs Pyrrhocorax pyrrhocorax in Corwall: Habitat use and food intake[END_REF][START_REF] Sanchez-Alonzo | An analysis of the diet of Redbilled Chough Pyrrhocorax pyrrhocorax nestling in NE Spain, using neck ligatures[END_REF], while in other locations they have been found to have a diet containing a mixture of plants and animals, with more insects taken during the breeding season and summer, and more plants taken in autumn and winter [START_REF] Warnes | Habitat use and food of choughs on the island of Islay, Scotland. In: Chough and land-use in Europe[END_REF][START_REF] Mccracken | An assessment of chough Pyrrhocorax pyrrhocorax diet using multivariate analysis technique[END_REF][START_REF] Blanco | Consumption rates of olives by choughs in central Spain : variations and importance[END_REF][START_REF] Soler | Diet of the Red-Billed Chough Pyrrhocorax pyrrhocorax in south-east Spain[END_REF][START_REF] Meyer | The diet of the chough Pyrrhocorax pyrrhocorax as indicated by analysis of digested prey remains[END_REF]. Some authors have suggested that changes in diet are due to a decrease in the availability of insects in autumn and winter [START_REF] Garcia-Dory | Datos sobre la ecologia del genero Pyrrhocorax (P. pyrrhocorax y P. graculus) en el parque Nacional de la Montana de Covodonga[END_REF][START_REF] Soler | Diet of the Red-Billed Chough Pyrrhocorax pyrrhocorax in south-east Spain[END_REF]. This was found to be the case in Ouessant, where the consumption of plants occurred in winter months when insect prey biomass was at its lowest. As found in other studies [START_REF] Warnes | Habitat use and food of choughs on the island of Islay, Scotland. In: Chough and land-use in Europe[END_REF][START_REF] Mccracken | An assessment of chough Pyrrhocorax pyrrhocorax diet using multivariate analysis technique[END_REF][START_REF] Soler | Diet of the Red-Billed Chough Pyrrhocorax pyrrhocorax in south-east Spain[END_REF][START_REF] Meyer | The diet of the chough Pyrrhocorax pyrrhocorax as indicated by analysis of digested prey remains[END_REF] Choughs, e.g. on Bardsey Island, Wales [START_REF] Roberts | Food of the chough on Bardsey Island, Wales[END_REF][START_REF] Roberts | Feeding habitats of the chough on Bardsey Island (Gwynedd)[END_REF], Pembrokeshire, Wales [START_REF] Meyer | The diet of the chough Pyrrhocorax pyrrhocorax as indicated by analysis of digested prey remains[END_REF], Cornwall, England [START_REF] Meyer | Observations on two Red-Billed Choughs Pyrrhocorax pyrrhocorax in Corwall: Habitat use and food intake[END_REF]), Islay, Scotland [START_REF] Warnes | A study of the ecology of the Chough Pyrrhocorax pyrrhocorax L. on the isle of Islay[END_REF][START_REF] Mccracken | Surface-active invertebrate communities and the availability of potential food for the Chough, Pyrrhocorax pyrrhocorax L., on pastures in north-west Islay[END_REF][START_REF] Mccracken | An assessment of chough Pyrrhocorax pyrrhocorax diet using multivariate analysis technique[END_REF][START_REF] Warnes | Habitat use and food of choughs on the island of Islay, Scotland. In: Chough and land-use in Europe[END_REF], the Italian Alps [START_REF] Laiolo | The diet of the chough (Pyrrhocorax pyrrhocorax) and the alpine chough (Pyrrhocorax graculus) in the alps: seasonality, resource partitioning and population density[END_REF], and Sar-plania and Perister, former Yugoslavia [START_REF] Matvejev | Le crave à bec rouge (Pyrrhocorax pyrrhocorax docilis GM.) en Yougoslavie[END_REF]. In those studies, Aphodius species occurred in Chough diet nearly all year round and often represented more than 90% of Chough prey. Conversely in Ouessant Aphodius appeared only in late autumn and winter, represented only 4% of prey identified in those months, and occurred in an average of only 17% of faecal samples analysed in the same months. This relatively rare occurrence of dung beetles in Chough diet in Ouessant is probably connected with the very low frequency with which Choughs are observed feeding on sheep-grazed pastures, a typical habitat for Aphodius. This avoidance of pastures could be explained by vegetation height, which often ranges from 10 to 40 cm due to the low grazing pressure in pastures on Ouessant.

Habitat attractiveness for Choughs is known to decrease with increasing vegetation height and the Chough selectivity coefficient for sward height has been found to be zero or negative above 10 cm [START_REF] Whithead | Choughs Pyrrhocorax pyrrhocorax breeding in Wales select foraging habitat at different spatial scales[END_REF][START_REF] Kerbiriou | Linking territory quality and reproductive success in the chough (Pyrrhocorax pyrrhocorax): implications for conservation management of an endangered population[END_REF]). In addition, the presence of dung beetles in Chough diet in autumn and winter on Ouessant is very likely linked to the particular sheep-grazing practices: in this season, sheep are left grazing freely on the island, and sometimes graze on coastal habitat. Hence, on Ouessant, dung beetles are available on coastal habitats only during this period and probably only in small numbers. This study also underlined the importance of ants Lasius flavus and Myrmica sabuleti which appeared to be the main food source from late spring to early autumn. In other studies, the importance of ants in Chough diet varied from total absence [START_REF] Warnes | Habitat use and food of choughs on the island of Islay, Scotland. In: Chough and land-use in Europe[END_REF] to the status of regular prey (most studies) or even major food source [START_REF] Cowdy | Ants as a major food source of the chough[END_REF]).

Diet at key periods of juvenile mortality

The analysis of monthly survival of juveniles during their first year identified three crucial months: August, November and December. On Ouessant, a high level of invertebrate biomass and a great variety of species occurred from the beginning of the nestling period through the time of juvenile fledging. This could partly explain the high survival rates of juveniles observed during this period. By contrast the amount of invertebrate biomass and the spectrum of prey species decreased during the summer. This was especially true in August, coinciding with the period when juveniles are left to feed themselves, when on Ouessant Choughs seem to depend mainly on ants and to a lesser extent on a few beetles such as Amara aenea, Steropus madidus and Calathus melanocephala. Emancipation of juveniles is known to be a period of high mortality in many bird species. This effect is reinforced in Ouessant, as emancipation occurs not only during a period when available prey biomass is greatly decreased, but also at a time when tourism disturbances are high (Kerbiriou et al. submitted).

August juvenile survival is noticeably lower in Ouessant than on the island of Islay, UK (Bignal et al. 1987, Kerbiriou et al. submitted) where studies have highlighted that newly fledged birds and subadults depend heavily on easily obtained prey items associated with livestock dung [START_REF] Mccracken | An assessment of chough Pyrrhocorax pyrrhocorax diet using multivariate analysis technique[END_REF]. Prey biomass reached its lowest level in November and December, when juvenile Chough survival was also found to be low. However, it should be noted that prey biomass in November and December was still comparable to (although a little lower than) that in September and October, when juvenile survival was much higher.

Hence, prey biomass might not be the only factor responsible for the low survival rates during November and December. At this time, a strong qualitative change in prey availability occurs, in terms not only of the species availability but also of where these species occur (Table 2).

The need to change to a different foraging strategy may also contribute to increased juvenile mortality, as juveniles focus on 'walker' species during summer, but then must complement their diet with 'burrower' species during the late autumn and winter. Tipulidae larvae (a burrower species) appear to be one of the main prey taken during this period, as previously observed in Islay [START_REF] Mccracken | An assessment of chough Pyrrhocorax pyrrhocorax diet using multivariate analysis technique[END_REF], Ramsey Island [START_REF] Meyer | The diet of the chough Pyrrhocorax pyrrhocorax as indicated by analysis of digested prey remains[END_REF], Bardsey Island [START_REF] Roberts | Food of the chough on Bardsey Island, Wales[END_REF] and in western Ireland [START_REF] Morgan | Chough digging for food in sand[END_REF]. Plants also appeared in Chough diet on Ouessant at that time, and this marked change in diet probably induces important changes in foraging behaviour and could also contribute to the reduction in juvenile survival. In Ouessant, monthly juvenile survival rates during November and December are lower than those in Islay, UK [START_REF] Bignal | Breeding success and post-fledging survival in the Chough (Pyrrhocorax pyrrhocorax)[END_REF]. One possible explanation for this could be that young birds in Ouessant are not used to the specific foraging behaviour necessary to obtain burrowing prey items. According to the diet composition during June and July [START_REF] Warnes | Habitat use and food of choughs on the island of Islay, Scotland. In: Chough and land-use in Europe[END_REF]) and foraging behaviour on Islay [START_REF] Bignal | The social life of the Chough[END_REF], non-emancipated juveniles in this Scottish island probably learn from their parents how to obtain invertebrates from the soil and from dung. Similar observations were made in Spain, where young Choughs appeared to be fed by their parents mainly with burrower prey items [START_REF] Sanchez-Alonzo | An analysis of the diet of Redbilled Chough Pyrrhocorax pyrrhocorax nestling in NE Spain, using neck ligatures[END_REF]. In addition, unlike on Islay, Choughs in Ouessant cannot forage on cereal grains since cropping on the island disappeared 50 years ago. Fledging success may also be influenced by feeding resources. Fledging success seemed to be influenced by total prey biomass availability rather than by the biomass of a specific prey group; this could be explained by the great diversity of spring invertebrates available. Compared to estimates of Chough fledging success at other locations, fledging success on Ouessant appeared to be among the lowest, regardless of whether fledging success of the whole population (1.37 ± 0.14 se at Ouessant; 2.02 in [START_REF] Reid | Environmental variability, life-history covariation and cohort effects in the red-billed chough[END_REF]1.88 found to be rather low on Ouessant. Thus, the variation in fledging success could be influenced either by chick survival at an early stage or by female physiological condition [START_REF] Reid | Environmental variability, life-history covariation and cohort effects in the red-billed chough[END_REF]). However, insufficient information is available to allow us to discriminate between these two hypotheses on Ouessant. Furthermore, the period influencing female body condition is unknown. Nevertheless, May, the feeding period of early chicks, appeared to be a potentially crucial period as prey biomass availability at this period influences fledging success.

Conclusion

This study highlights that on Ouessant prey biomass availability affects Chough demographic parameters such as fledging success and, most likely, juvenile survival in the first year after fledging. In addition, Chough diet appeared to be dominated by very few prey species, which put constraints on juvenile survival during periods when those prey species were absent or rare. This relationship probably affects the viability of the very small Chough population in Brittany. However, further detailed information is needed before it is possible to quantify the consequences of fluctuations in these key prey items on juvenile Chough survival, or to understand how fluctuations in prey availability are related to environmental changes. To this end, further detailed studies of annual variation in prey availability during August, November and December are required.

LEGENDS TO FIGURES

  Ouessant breeding Chough population was systematically surveyed from 1996 to 2003 (about 13 breeding pairs each year) and the number of fledglings determined for each nesting attempt. Between 1998 and 2003, all accessible juveniles were colour-ringed before fledging(n = 73, 67% of fledglings). Juvenile survival was estimated from resighting records (based on year-round resighting, about 2500 records), using the MARK program[START_REF] White | Program MARK: survival estimation from populations of marked animals[END_REF]. The model selections approach used in this program identifies the factors (e.g. month and year of birth) statistically associated with survival and resighting rates. To select the best model, we used Akaike's procedure[START_REF] Burnham | Model selection and inference, a practical information-theoretic approach[END_REF], which allows comparison of non-nested models according to their Akaike information criterion (AIC) corrected for small sample size. Models with low AICc are considered a good compromise between parsimony (low number of parameters in the model) and adequate fit to the data (low deviance). The AIC weight indicates the relative likelihood of each model given the data, and

  1998 and 2003, only two colour-ringed Choughs were resighted outside Ouessant. They were detected together in August 2001 after being last seen in Ouessant in July 2001. These two ringed birds were subsequently resighted many times by at least five independent observers within four months. The same was true for the mainland population, where colourmarked birds (n = 10) were resighted often but never recorded on Ouessant. This indicates that although dispersal outside Ouessant is possible, it is rare, and that observation pressure on Chough habitat is sufficient that such dispersal events are unlikely to remain undetected.Variation in juvenile survival was studied by ringing birds in nests in mid-May and recording resighting of those birds until June of the following year. The AICc in Table3indicated that the most parsimonious model included additive effects of month and year (equivalent to cohort) on juvenile survival. Yet, the goodness-of-fit test (χ2 = 37.32, df = 18, P =0.005) indicated a significant deviance from the full model, indicating that an additional source of variationin survival remained to be identified. Monthly survival variation of Choughs in their first year (from ringing day in May to June of the next year, i.e. 13 months) identified two crucial periods during which survival rates were low: August (survival rate = 0.57) and

Figure 2 :Figure 3 :Figure 4 :Figure 5 :

 2345 Figure 2: PCA axis 1 and axis 2 scores indicating the seasonal breackdown of Chough diet

Table 1

 1

, Fig.

1

): diet in spring consisted mainly of Coleoptera, spiders, ants and Diptera (mostly Tipulidae larvae), whereas in summer the diet was dominated by ants. In autumn, ants occurred together with beetles and plants. In winter, flies (Tipulidae larvae) contributed a great part to the diet composition. To investigate seasonal variation in diet composition in greater detail, a principal component analysis (PCA) was used to analyse frequency of occurrence of prey in the 437 faecal samples (Fig.

2

). The two first axes of this PCA explained 26.7% and 18.2% of the variance, respectively. The analysis isolated three groups. (i) The summer-early autumn group (July to October) consisted mainly of ants Lasius flavus and Myrmica sabuleti, ant eggs and Coleoptera Calathus melanocephalus, Steropus madidus, Amara aenea. (ii) The late autumnwinter group (November to March) consisted mainly of Tipulidae larvae, plants, dung beetles (Aphodius spp., Onthophagus spp., Thyphoeus thyphoeus, carabidae beetle Leistus fulvibarbis, Cymindis axillaris, Nebria brevicollis and weevil Oniscus asellus. (iii) The spring group (April to June) included numerous species with spring activity, such as Coleoptera Rhyzotrogus aestivus, Cetonia maura, Cetonia aurata, Hister quadrimaculatus, Adelocera murina, Agriotes gr-lineatus and also spiders, such as Lycosidae Trochosa terricola, Pardosa

sp. We then considered variation in the type of prey occurring in Chough diet during the three time periods. Invertebrates were assigned to one of three classes according to their ecology: (i) the 'burrower' group, including species such as beetle larvae, Tipulidae larvae and dungdwelling species; (ii) the 'walker' group, including species with important soil activities such as Lycosidae spiders, Carabidae beetles and ants; (iii) the 'other' group, including species waiting in ambush for their prey, such as Thomisidae spiders. Choughs generally captured mainly invertebrates of the 'walker' group, except during the winter period when burrowers represented nearly half of the prey, Table

  On Ouessant rabbits occurred mainly on abandoned agricultural land but could also be seen on the coast and could be an additional source of this prey for Choughs. Other coleoptera were essentially represented by larvae. Dung beetles (scarabs Aphodius spp., Onthophagus spp., Geotrupes pyrenaeus, Typhoeus typhoeus) represented a very small component of the Chough diet in Ouessant and occurred mostly in winter. This observation contrasts with most other studies which have found dung beetles to be a major food source for

	, this
	study indicated that adult beetles are one of the most important prey items for Choughs on
	Ouessant. Some beetles occur in the diet in large proportions, such as Amara aenea in
	summer, or Rhyzotrogus aestivus, Cetonia aurata, Agriotes gr-lineatus, Adelocera murina

and Hister quadrimaculatus in spring. Conversely, very few species of adult beetle occurred in Chough diet in winter: Typhoeus typhoeus appeared to be an important prey during this period. T. typhoeus is often associated with rabbit colonies and their dung

(D.I. McCracken pers. comm.)

  to 2.85 in[START_REF] Bullock | The chough in Britain and Ireland[END_REF] or fledging success of successful breeders (2.48 ± 0.11 se at Ouessant; 2.68 in DeSanctis et al. 1997; 2.60 in Laiolo & Rolando 2001) is considered. Fledging success is a combination of the breeding pair's 'quality' (e.g. female body condition, parental care experience) and the amount of food brought to the nest. Juvenile mortality in June (i.e. the three last weeks in the nest and the first days after fledging) was

Table 1 :

 1 Proportion of faecal samples analysed each month which contained each prey item.

	Taxon	Moving Encoded January February March April May	June	July	August September October November December
		group	name
	Sample number			34	16	40	58	107	35	32	40	24	6	31	14
	PLANTS			0,24	0	0,05	0	0	0	0	0	0	0,50	0,23	0,57
	OLIGOCHAETA	Burrower oligo	0,06	0	0	0,05 0,01	0	0	0	0	0	0,03	0,07
	ARACHNIDA
	Drassodes cupreus	Walker dracup	0	0	0	0,02	0	0	0	0	0	0	0	0
	Trochosa terricola	Walker	troter	0	0	0,03	0,07 0,01	0,03	0	0	0	0	0	0
	Xystichus erraticus	Other	xyserr	0	0	0	0	0,01	0	0	0	0	0	0	0
	Dysdera spp	Other	dyssp	0,03	0	0	0	0,03	0,06	0,06	0,05	0	0	0,03	0,21
	Pardosa spp	Walker	parsp	0	0	0	0	0,05	0	0	0	0,17	0	0	0
	Indeterminate	Walker	arasp	0,24	0,06	0,08	0,48 0,44	0,26	0,22	0,35	0,21	0	0,19	0,29
	OPILINIDA
	Homalenotus quadridentatus	Walker homqua	0	0	0	0,02	0	0	0	0	0	0	0	0
	CRUSTACEA
	Oniscus asellus	Walker oniase	0,03	0,06	0,03	0	0	0	0	0	0	0	0	0,14
	MYRIAPODA
	Cylindroiulus latestriatus	Walker	iule	0,03	0,19	0,08	0,04 0,01	0	0	0	0	0,17	0	0,14
	Lithobius forficatus	Walker	litfor	0,12	0	0,03	0,09 0,03	0,03	0,03	0,05	0,25	0	0,03	0,36
	LEPIDOPTERA
	Larvae	Walker	larle	0	0	0,05	0,11 0,04	0,29	0	0,03	0,04	0	0	0
	COLEOPTERA
	Carabidae
	Amara aenea	Walker amaae	0	0	0,08	0,02 0,22	0,03	0,19	0,27	0	0	0,06	0
	Anisodactylus binotatus	Walker		0	0	0	0	0	0	0	0	0	0	0	0
	Calathus melanocephala	Walker	calmel	0,03	0	0	0	0	0	0	0,14	0,33	0,33	0,10	0,07
	Cymindis axillaris	Walker cymaxi	0,06	0,06	0,05	0	0	0	0	0	0	0	0	0,07
	Cicindella campestris	Other	ciccam	0	0	0	0	0,01	0	0	0	0	0	0	0
	Steropus madidus	Walker stemad	0		0,03	0	0,02	0,06	0,44	0,30	0,13	0	0	0
	Poecilus cupreus	Walker poecup	0	0	0	0	0,02	0,03	0	0	0	0	0	0
	Nebria brevicollis	Walker	nebre	0,06	0	0,05	0,02	0	0	0	0	0	0	0	0,07
	Harpalus rubripres	Walker	harrub	0	0	0	0	0,09	0	0	0	0	0	0	0
	Leitus fulvibarbis	Walker	leiful	0	0	0	0	0,01	0	0	0	0	0	0	0,07
	Staphylinidae
	Ocypus olens	Walker	ocyol	0,03	0	0,03	0,02	0	0	0	0	0	0,33	0,03	0
	Philonthus intermedius	Walker	phiint	0,15	0,13	0,10	0,04 0,09	0,03	0,06	0	0,13	0	0,06	0,14
	Indeterminate	Walker		0	0	0,03	0	0,01	0	0	0	0	0	0	0
	Elateridae
	Adelocera murina	Walker adelmur	0	0	0	0,05 0,46	0,35	0,03	0,24	0	0	0	0
	Agriotes gr-lineatus	Walker	agrgrl	0,12	0	0	0,02 0,16	0,09	0	0,08	0	0	0	0
	Athous haemoroides	Walker	athha	0	0	0	0,04 0,09	0,03	0,03	0	0	0	0	0
	Geotrupidae/Scarabidae
	Aphodius spp	Burrower aphod	0,18	0,19	0,15	0	0	0	0	0	0	0	0,03	0,29
	Cetaunia aurata	Walker	cetaur	0	0	0	0	0,08	0,62	0	0	0	0	0	0
	Cetonia morio	Walker cetmor	0	0	0	0	0,01	0,06	0,06	0	0	0	0	0
	Geotrupes pyreneaeus	Burrower geopyr	0	0	0	0,13 0,04	0,12	0,03	0	0	0	0	0
	Onthophagus spp	Burrower ontho	0	0	0,05	0	0,03	0	0	0	0	0	0	0,21
	Rhyzotroglus aestivus	Walker rhyaes	0	0	0	0	0,47	0,35	0	0	0	0	0	0
	Typhoeus typhoeus	Burrower typtyp	0,29	0	0,05	0,02	0	0	0	0	0	0	0,29	0,29
	Cucurlionidae
	Indeterminate	Walker cuccur	0,03	0	0,05	0,02 0,07	0,03	0,03	0,16	0	0	0,03	0,14
	Tachyphloeus spp	Walker	cucur	0,03	0	0,15	0	0,03	0	0	0	0,08	0	0	0
	Otiorhynchus spp	Walker	cucur	0,06	0,13	0	0,04 0,06	0	0,09	0,14	0,13	0	0	0
	Tenebrionidae
	Opatrum sabulosum	Walker opasab	0	0	0	0,02 0,04	0,04	0	0	0	0	0	0
	Nalassus laevioctostriatus	Walker	nallae	0,06	0,06	0,05	0,07 0,17	0,12	0,06	0,05	0,13	0	0,03	0,07
	Histeridae
	Hister quadrimaculata	Walker hisqua	0	0	0	0,09 0,37	0,06	0	0	0	0	0	0
	Oedemeridae
	Psilotrix viridescens	Other	Psivir	0	0	0	0,02 0,02	0,06	0	0	0	0	0	0
	Indeterminate adult	Walker		0,06	0	0,08	0,16 0,07	0,09	0	0,03	0,13	0,17	0,23	0
	Indeterminate larvae	Burrower larcol	0,24	0,06	0,30	0,41 0,10	0,32	0,06	0	0	0	0,10	0,07
	DERMAPTERA
	Forficula auricularia	Walker	forau	0,03	0	0	0,02 0,04	0,09	0	0	0	0	0,03	0
	HYMENOPTERA
	Eumenidae	Other hymeum	0	0	0	0	0,01	0	0	0	0,04	0	0	0
	Formicidae
	Eggs	Burrower foregg	0	0	0	0,02 0,01	0,06	0,31	0,22	0,08	0	0	0
	Lasius flavus	Walker	lasfla	0,03	0	0	0,09 0,16	0,29	0,97	0,86	0,42	0,67	0,39	0
	Myrmica sabuleti	Walker myrsab	0	0	0,03	0,02 0,04	0,12	0,13	0,16	0,29	0	0	0
	DIPTERA
	Inderterminate adult	Walker	dipt	0	0	0	0	0	0,03	0	0	0	0	0	0,07
	Tipulidae larvae	Burrower lartip	0,59	0,94	0,85	0,38 0,03	0	0	0	0	0	0,32	0,14

Table 2 :

 2 Relative importance of each of three prey classes in chough diet on island of

	Ouessant
		April to June	July to October	November to March
	Burrower	5.0	1.5	46.6
	Walker	94.8	98.1	49.5
	Other	0.2	0.4	3.9

Table 3 .

 3 Model selection for juvenile survival variation,  AICc . is the difference of AIC between the considered model and the best one. Diet of the chough in Ouessant expressed as the proportion of the total number of individuals counted in the faecal samples analysed each month.

	Model	AIC		N	Deviance	AICc
		c	AICc	P		Weight
	S[month+	249.	0.00	18	37.32	0.98
	year]	49
	S[month]	267.	7.59	13	55.61	0.02
		08
	S[year]	333.	73.7	6	136.39	0.00
		25	6
	S[.]	343.	84.0	1	156.83	0.00
		52	3
	S[month*	371.	112.	78	0.00	0.00
	year]	49	00

ACKNOWLEDGEMENTS

Special thanks are due to Jean-Yves Monat and Jacques Nisser for help with ringing techniques. We thank the following persons for sightings of marked Choughs: A. Audevard, M. Champion, D. Cohez, F. Duruz, P. Gaultier, Y. Jacob, J. P. Jordan, D. Laloi, V. Le Pennec, I. Le Viol and D. Matti. We thank G. Tiberghien, I. Le Viol and V. Le Pennec for valuable help in identification of invertebrates, and F. Jiguet for help in PCA analysis. We thank Frédéric Bioret for assistance in the realization of botanical typology of the Chough habitat, and Emmanuelle Porcher, Peter Vickery and Davy McCracken for insightful comments and discussion on earlier drafts of this manuscript.


Kerbiriou Christian
email: kerbiriou@mnhn.fr

Gourmelon Françoise

Bioret Frédéric

Linking territory quality and reproductive success in the chough (Pyrrhocorax pyrrochorax): implications for conservation management of an endangered population

Keywords: territory quality, Pyrrhocorax pyrrochorax, Core-weighting kernel method

As changes in land uses have been mentioned as the main factor to explain decline of chough population across western Europe, a study was carried out in Ouessant (western France) in order to link territory quality with reproductive success. As such an approach could be hindered by the fact that reproductive performance of birds could be influenced by their breeding experience, we analysed both inter-and intra-nest site variation in fledging success.

Territory quality was quantified combining habitat selection, territory size, amount of feeding area and distance between nest and feeding area.

Feeding habitats positively selected by chough were characterized by a mean sward height lower that 5cm. Foraging area was on average of 21,557 m². Feeding areas (ie. feeding habitat within foraging area) close to the nest were preferentially used. Fledging success appeared not to be influenced by the total area of feeding areas in chough territory, nor by the mean feeding flight distance. But fledging success adjusted to nest site and year appeard to be influenced by feeding area close to the nest : one additional fledging was expected for each additional 10,000 m² of feeding habitat within 300m of the nest. These first results bring elements which allowed us to consider recommend landscape management measures to ensure a favourable conservation status of local chough populations.

INTRODUCTION

Habitat loss and damage linked to changes in agriculture practices are the most frequently reported threats affecting European birds species [START_REF] Baillie | Breeding birds in the wider countryside : their conservation status 2000[END_REF][START_REF] Bignal | Low-intensity farming systems in the conservation of the countryside[END_REF][START_REF] Pain | Farming and birds in Europe[END_REF][START_REF] Newton | Rodenticides in British Barn Owls[END_REF][START_REF] Shrubb | The Kestrel[END_REF][START_REF] Tucker | Effects of agricultural practices on filed use by invertebrate-feeding birds in winter[END_REF][START_REF] Tucker | Birds in Europe their conservation status[END_REF][START_REF] Newton | The recent declines of farmland bird populations in Britain : an appraisal of causal factors and conservation actions[END_REF][START_REF] Gregory | The state of play of farmland birds : population trends and conservation status of lowland farmland birds in the United Kingdom[END_REF]. European agriculture has been intensified drastically in recent decades although, paradoxically, agricultural abandonment has also occured as an indirect effect of intensification, as some marginal lands became less profitable to farming and are therefore set aside [START_REF] Bignal | Transhumance in Spain[END_REF][START_REF] Blanco | Traditional farming and key foraging habitats for chough Pyrrhocorax pyrrocorax conservation in a Spanish pseudo steppe landscape[END_REF]. In order to ensure favourable conservation status for threatened bird species in Europe, the European Commission requires member states to designate Special Protection Areas -SPAs-to protect endangered habitats and species, especially for birds listed in the Directive of the council of the European Community on the conservation of wild birds (Directive 79/409/CE). As most European areas are directly or indirectly concerned by agricultural practices, such conservation measures also receive support from EU countries through management agreements under the agri-environment regulation (EC reg. 1765/92) of the Common Agricultural Policy. The efficiency of the conservation planning emerging from such agricultural policy should be determined by comparing ecological knowledge on population dynamics and the corresponding effects of habitat management. [START_REF] Barber | Nestling success of birds in different silvicultural treatments in southeastern U.S. pine forest[END_REF][START_REF] Davis | Nest-site selection patterns and the influence of vegetation on nest survival of mixed-grass prairie passerines[END_REF][START_REF] Driscoll | Determinants of wood thrush nest success: a multi-scale, model selection approach[END_REF][START_REF] Rodewald | Avian nestling success in forested landscapes: influence of landscape composition, stand and nest-patch microhabitat, and biotic interactions[END_REF], This is particularly the case for the chough (Pyrrhocorax pyrrhocorax), a species listed in Annex I of the European Community Birds Directive. Its populations are scattered and most of them show long-term decline. Many studies have highlighted the ecological needs of the chough in low-intensity farmland habitats, such as undisturbed rough grass and short grazed pasture [START_REF] Warnes | A study of the ecology of the Chough Pyrrhocorax pyrrhocorax L. on the isle of Islay[END_REF], Mc Cracken et al. 1992[START_REF] Rolando | The foraging behaviour of the chough Pyrrhocorax pyrrhocorax in two contrasting habitats[END_REF][START_REF] Bignal | Feeding behavior of nestling choughs in the Scottish Hebrides[END_REF], Robertson et al. 1995[START_REF] Blanco | Traditional farming and key foraging habitats for chough Pyrrhocorax pyrrocorax conservation in a Spanish pseudo steppe landscape[END_REF][START_REF] Madders | Distribution and foraging habitat preferences of Choughs on the Oa peninsula, Islay[END_REF][START_REF] Whithead | Choughs Pyrrhocorax pyrrhocorax breeding in Wales select foraging habitat at different spatial scales[END_REF]. In addition, local population trends have been linked to a range of factors such as weather conditions [START_REF] Owen | Factors affecting the status of the chough in England and Wales[END_REF], Reid et al. 2003a), human persecution [START_REF] Owen | Factors affecting the status of the chough in England and Wales[END_REF]) and, chiefly, grazing pressure [START_REF] Bullock | The chough in Britain and Ireland[END_REF][START_REF] Cullen | The history and present status of the chough in the Isle of Man. 19-22[END_REF][START_REF] Owen | Factors affecting the status of the chough in England and Wales[END_REF][START_REF] Berrow | The second international Chough survey in Ireland[END_REF][START_REF] Cook | Status, distribution and breeding success of the Red-billed Chough in Scotland in[END_REF][START_REF] Mccanch | The relationship between Red-Billed Chough Pyrrhocorax pyrrhocorax (L) breeding populations and grazing pressure on the Calf of Man[END_REF]. In general, population declines are believed to be due to changes in land use of agricultural landscapes, such as farming intensification or the loss of grazing practices [START_REF] Rolfe | Status of the Chough in Scotland[END_REF][START_REF] Garcia-Dory | Datos sobre la ecologia del genero Pyrrhocorax (P. pyrrhocorax y P. graculus) en el parque Nacional de la Montana de Covodonga[END_REF], Mc Cracken et al. 1992[START_REF] Meyer | The diet of the chough Pyrrhocorax pyrrhocorax as indicated by analysis of digested prey remains[END_REF][START_REF] Dendaletche | Alpine Chough and Choughs : biological integrators of agropastoralism ecosystems in the Pyrenees[END_REF], [START_REF] Blanco | Traditional farming and key foraging habitats for chough Pyrrhocorax pyrrocorax conservation in a Spanish pseudo steppe landscape[END_REF], Kerbiriou 2001). However, we still have little knowledge of possible processes driving these declines in terms of population dynamics, and only a handful of studies have directly examined habitat characters affecting demographic parameters [START_REF] Mccanch | The relationship between Red-Billed Chough Pyrrhocorax pyrrhocorax (L) breeding populations and grazing pressure on the Calf of Man[END_REF], Reid et al. 2003a, Reid et al. 2003b). A major long-term study of individually-marked chough, carried out on Islay (United Kingdom) has highlighted the consequences of environmental variability (as temperature and rainfall variations during the pre-breeding season) on demographics parameters such as fledging success, first-year survival and individual life-time reproductive success (Reid et al. 2003a.).

It is puzzling that the main study available about demographic process affecting the short term populations dynamics has shown that the most important explanatory factor is natal weather conditions, (Reid et al. 2003a), whereas at the population level, the main external factor cited to explain population trends is change in land use. Such differences between conclusions of studies based on distribution and abundance and studies based on demographic parameters are probably explained by the focus of the latter on short-term inter-annual variations, while habitat variation occurs at a longer time scale.

A way to solve this apparent paradox would be to link spatial variation in demographic parameters among breeders and variations in territory quality. Choughs need cavities for nesting and short vegetation for foraging. We predicted variations in territory quality among different breeding pairs according to these parameters. We quantified territory quality combing estimation of foraging area and feeding habitat, taking account distance to the nest.

We then studied variation in breeding success in relation with our measure of territory quality.

We used our result to suggest landscape management recommendations for chough based on these analyses

METHODS

The biological model

The red-billed chough is a medium-sized corvid with a patchy distribution throughout its European range. The estimated minimum European population size is 16,000 pairs, confined to remote areas mostly in mountains and along coasts. Over half of this population is concentrated in Spain, Greece and Italy, while most other populations are small and declining (Tucker and Health 1994). This scattered distribution results from the ecological needs of the species, involving a combination of suitable nesting sites (shallow caves in cliffs) and suitable foraging areas (short grassland vegetation with low cover; [START_REF] Roberts | Feeding habitats of the chough on Barsey Island (Gwynedd)[END_REF][START_REF] Farinha | the chough in Portugal -Status and distribution. 25-28[END_REF][START_REF] Rolando | The foraging behaviour of the chough Pyrrhocorax pyrrhocorax in two contrasting habitats[END_REF][START_REF] Bignal | The social life of the Chough[END_REF][START_REF] Blanco | Traditional farming and key foraging habitats for chough Pyrrhocorax pyrrocorax conservation in a Spanish pseudo steppe landscape[END_REF][START_REF] Whithead | Choughs Pyrrhocorax pyrrhocorax breeding in Wales select foraging habitat at different spatial scales[END_REF]. The small Western French population is confined to very few localities in Brittany, and appears to be one of the smallest cluster and the most isolated population in Western Europe [START_REF] Tucker | Effects of agricultural practices on filed use by invertebrate-feeding birds in winter[END_REF]Heath 1994, Kerbiriou 2001). It suffered a large decrease after the 1960s, from probably 100-150 to about thirty pairs two decades later. Currently, this population seems to be stabilised at a low level of 39-55 breeding pairs [START_REF] Kerbiriou | Recensement 2002 de la population bretonne de crave à bec rouge (Pyrrhocorax pyrrhocorax)[END_REF]. These birds are highly faithful to site and mate, they breed once each year and they rarely skip breeding years as observed elsewhere [START_REF] Roberts | The Choughs of Bardsey[END_REF][START_REF] Bignal | The social life of the Chough[END_REF], Reid et al. 2003a).

Study area

Our study was conducted on the island of Ouessant, a small island (1,541 ha) 20 km from the western tip of Brittany, France (48°28'N , 5°5' W). It shelters one of the cores of the Brittany chough population (Kerbiriou 2001), with an average of 13 breeding pairs. Important land use changes occurred on the island after the decline of the human population since the beginning of the 20 th century. This led to a complete disappearance of crop farming, a drastic decrease in grazing pressure (sheep numbers decreased from 5,900 in 1950 to 650 in 2003). Pastures were formerly located along the coastal strip, but moved inland closer to human settlements, while crop abandonment and low grazing pressure created fallow lands, dominated by bracken (Pteridium aquilinum) and brambles (Rubus fructicosus) which now occupy more than half of the island area [START_REF] Gourmelon | Land-use changes and implications for management of a small protected island off the coast of Bretagne[END_REF].

Vegetation coverage

A vegetation map was created using field plotting and aerial ortho-photograph (IGN 2002) interpretation, implemented in a Geographical Information System (Arc-Info, Environmental

Research System Institut Inc). Chough feeding habitats were categorized according to vegetation cover, vegetation height and floral composition. Seven habitat classes were determined (Table 1). As paths could not be accurately digitalised directly from aerial photographs, they were first defined as lines. In a second step, field measurement of path width were made, as well as a recording of their eventual vegetation cover. A polygon cover of paths was then created as a buffer along the path linear cover using data on path width and state. The final chough habitat cover was obtained by up-dating the vegetation cover with the polygon path cover. Except for restored habitats, changes in coastal vegetation can be considered as insignificant during the study period (1998)(1999)(2000)(2001)(2002)(2003), most habitats (heathland, short and rocky vegetation, grassland...) evolve slowly or even not at all, and could be considered as perennial vegetation. Restored habitats were located at the south west tip and account for a small area (77,466m², i.e. 2.9 % of coastal vegetation).

Chough survey and focal sampling of behaviour

To allow the study of reproductive performance variation among breeding pairs, all nests (about 12 per year) were found and the number of fledged offspring was recorded yearly from 1998 to 2003 for each pair.

We wanted to assess distribution of foraging habitat within the territory used by a pair during the breeding period. We conducted each year several survey sessions for each pair during the breeding period (mid April to early July), totalling 318 sessions from 1998 to 2003 (average 4.5  0.18 SE per pair and per year). During a survey session, a team made of two to six people (depending on preliminary field knowledge of the size of the territory), connected by radio was settled close to but out of the potential foraging area. Survey were carried only in good weather (no rain, light wind and avoiding low or high temperature). During each session, the pair was surveyed for 1.5 hours(1 h 29  3 SE min), giving a total of 802 hours of male and female survey from 1998 to 2003. Pairs were identified according to the nest they occupied; some were also identified by individual colour-rings. During a session, we performed focal sampling of behaviour (categorized as feeding, resting, flying, parental care, interaction with other choughs or other animals) as well as the time spent for each of these activities. For each foraging behaviour, habitat used by chough was noticed. Only feeding behaviours were further considered to model territory usage. Every 30 seconds, the location of feeding male and habitat used were considered for territory modelling. These feeding observations were then plotted on a digitised map of the study area, using aerial orthophotographs, implemented in a GIS.

Estimating foraging area of breeding choughs

As defining and estimating foraging area of breeding pairs was crucial for the purposes of this study, we had to assess the reliability of the data and of the method we used to obtain ranges.

While the female incubates the eggs, the male forages within home range and feeds the female at, or close to, the nest. When females feed by themselves, it is mostly close to the nest. After egg-hatching, the male keeps on regurgitating food to the female, who in turn feeds the newlyhatched chicks. During the second half of the rearing period, male and female forage close together, and make regular foraging trips to areas in their home range in order to collect food, and then feed the nestlings by regurgitation. Therefore, foraging area was modelled with data from feeding male only, as female feeding locations could have biased the foraging area delimitation by bringing a set of locations either concentrated around the nest or similar to those of males.

We choose contouring methods to measure chough foraging area because these methods have considerable advantage over other popular home-range estimation methods such as the minimum convex polygon [START_REF] Hemson | Are kernels the mustard? Data from global positioning system (GPS) collars suggests problems for kernel home-range analyses with lest-square cross validation[END_REF]. They do not rely on outlying points to anchor their corners and are less influenced by distant points, thereby excluding unused areas, leading to more accurate depictions of space use [START_REF] Hemson | Are kernels the mustard? Data from global positioning system (GPS) collars suggests problems for kernel home-range analyses with lest-square cross validation[END_REF]. Foraging areas were modelled using Ranges V package [START_REF] Kenward | Originalité de la population bretonne de crave à bec rouge dans un contexte européen[END_REF], using the kernel density estimator, an estimator viewed as the most reliable contouring methods in ecology [START_REF] Worton | Kernel methods for estimating the utilization distribution in home range studies[END_REF][START_REF] Boulanger | A comparison of home-range estimators using Monte Carlo simulation[END_REF][START_REF] Worton | Using Monte Carlo simulation to evaluate kernel-based home range estimators[END_REF][START_REF] Powell | Animal home ranges and territories and home range estimators[END_REF][START_REF] Kernohan | Analysis of animal space use and movements[END_REF]. Kernel density estimation creates isopleths of intensity of utilization by calculating the mean influence of data point at grid intersection. Each isopleth contains a fixed percentage (e.g.95%) of utilization density suggestive of the amount of time that the animal spends within the contour [START_REF] Hemson | Are kernels the mustard? Data from global positioning system (GPS) collars suggests problems for kernel home-range analyses with lest-square cross validation[END_REF]. Core-weighting kernel method was chosen (rather than fixed or tail-weighting kernel) because it minimises the risk of over-estimating foraging area size because of isolated outlying locations (fig. 1; see e.g. [START_REF] Jiguet | Lek mating system a case study in the little bustard Tetrax tetrax[END_REF]. Such isolated contact points are most probably not connected to the main feeding range but correspond to occasional movements of males defending their territories because of the close proximity of neighbouring breeding pairs. In addition, we considered the isoline of 95% point density to obtain size of foraging area. Considering the additional 5% point density increased foraging areas sizes more than twice (2.18  0.13 factor). Furthermore, 100% foraging areas are largely overlapping between pairs, which is biologically unlikely due to the strong territorial behaviour of the species (Fig. 1).

Randomisation test were used to assess the number of visits necessary to give robust foraging area estimate: 4 survey sessions distributed along the reproduction season was found as the best compromise between effort and precision (Appendix 1).

This protocol allowed us to model all breeding chough territories of Ouessant from 1998 to 2003, except in 2000 when home ranges could be estimated for only 5 of the 12 breeding pairs. Altogether, 68 different home ranges could be computed .

Feeding areas of each pair and for each year were mapped on the digitalised map using the GIS and the cross-cutting with the habitat cover layer allow then to obtain data on areas covered by each habitat type in each foraging area.

Habitat selected for foraging was further studied through the comparison between the area (in m²) present in the territory, deduced from vegetation map and the time (in s) spent foraging by each member of the pair in the different habitats recorded during the field-survey. Comparison was done on a Logit scale as follow :

Logit Index of Habitat H = Σi,t [[ln(Si,t/(100-Si,t)]-[ln(Fi,t/(100-Fi,t)]]/(n).
n is the number of nest survey during the study (68). Fi,t is the percentage of time spend by a breeding pair (i) the year (t) in the habitat H. Si,t is the percentage of areas cover by the habitat H in the territory of the pair (i).

Statistical analysis

We used ANOVA to explore variations in fledging success in relation with territory quality.

The fledging success of a nest was estimated as the number of young fledging from this nest, (ranging from 0 to 4). Territory quality was estimated as the total optimal foraging habitat areas (m²) present in the foraging area of each breeding pairs, or as the mean lenght of a foraging trip(m) or as the optimal foraging habitats area present in the foraging area close to the nest (within a radius of 300 meters). These analyses were controlled for year effect (year was considered as a factor).

The study of heterogeneity in demographic parameters among breeders, and its link to variations in territory quality, could be complicated by influences of age, breeding experience, territory ownership duration or pair bond duration, on demographic parameters such as reproductive performance (Reid et al. 2003b[START_REF] Cam | Apparent inferiority of first-time breeders in the kittiwake : the role of heterogeneity among age classes[END_REF][START_REF] Black | Fitness consequences of long-term pair bonds in barnacle geese: monogamy in the extreme[END_REF][START_REF] Pyle | Effects of age, breeding experience, mate fidelity and site fidelity on breeding performance in a declining population of Cassin's auklets[END_REF]. Unfortunately, very few individual histories were known in the studied population because must breeders were not colour ringed. When relationships between habitat quality and demographic parameters were analysed we attempted to avoid this pitfall by considering internest variations (the average variations between the different nests, test were nested to the nest site effect) and intra-nest variations (i.e. residual variation after controlling for nest site effect) separately.

.

RESULTS

Habitat selection.

In order to evaluate the feeding quality of each territory, it was first necessary to identify which habitats were used by feeding choughs. Breeding birds spent 71% of their foraging time in various habitat types all characterized by vegetation under 5 cm high : paths, rocky short grasslands and short grasslands . Secondary habitats used for foraging were short heathland and littoral grasslands. Other habitats such as pastures and medium heathland represented less than 1% of the observations. Habitat selection by foraging chough could be evaluated through the comparison between the areas (m²) present in each territory and the time each breeder spent foraging in the different habitat types. Again the same three habitats appeared to be positively selected by chough (Fig. 2). These three habitat types were pooled together to describe territory quality in subsequent analyses.

Home ranges of breeding pairs

Foraging areas sizes estimated with Core-weighting Kernel method, varied from 3587 to 67,388 m² (mean : 21,557 m² ± 1 645 SE). Within these foraging areas, the foraging habitat area covered by habitats identified as optimal for foraging (i.e. with a vegetation height below 5cm) varied from 516 to 61 200m² (mean : 17,439 m² ± 1 503 SE). The territory with the smallest optimal foraging area come from a pairs which had used mostly secondary habitat.

Year to year changes.

Vegetation cover at given place did not vary between year. But foraging area of pair breeding at the same nest site could vary quite much (Fig. 3) presumably because of changes in local social structure, such as disappearance of a breeding pairs and the appropriation of territory by the neighbouring breeding pair as illustrated in Figure 3a. Changes in the territory quality can also occur when dominant behaviour between two pairs change as showed in Figure 3b.

These examples (Fig. 3) show that chough territory is not only constrained by the location of nest site, but mostly influenced by the presence of breeding choughs in the neighbourhood.

Distances between nests and feeding areas.

The median value of the distances measured between nests and feeding areas was 230 m, while 59% of breeding choughs are observed feeding less than 300 m from their nest. Only less than 1% of the 3700 observations were farther than 1800 m from the nest (the largest distance was 5113 m). Average foraging distance varied from 125 to 3128 m (489 ± 56 SE m).

Influence of quality territory on fledging success.

We analysed variation in fledging success as a function of territory quality with fledging success. Fledging success appeared to be influenced by nest-site identity, but we did not detected any year effect (Table 2). We attempted to explain inter-nest variation in fledging success with the average parameter over year calculated for each nest. Total area of favourable foraging habitat in foraging area appeared not to influence significantly fledging success (Table 2), very likely due to important nest-site effect, but the correlation was slightly positive. Average fledging success was not influenced by the mean distance covered by pairs during breeding period (Table 2). As most choughs were observed feeding less than 300 meters away from their nest, we retained this distance class, to test the possible effects of the amount of optimal foraging habitats within a 300m radius from the nest on fledging success.

But again this estimated of territory quality (feeding area close to the nest), did not explain inter-nest variation (Table 2).

A second approach focussed on intra-nest variation in fledging success : Fledging success adjusted to nest and year appeared not to be influenced by the total area of favourable foraging habitat in foraging area (Table 2). Fledging success adjusted to nest and year was not influenced by the mean distance covered by pairs during breeding period (Table 2). But fledging success adjusted to nest and year appeared to be influenced by the amount of optimal foraging area close to the nest, a quite important variation is explain by this effect : R² = 0.6196 (Fig. 4 ; Table 2).

However, it can be noted that intra and inter-variation of fledging success according to optimal favourable habitat close to the nest showed a similar slope (respectively 1.0 ± 0.7 SE and 1.4 ± 0.7 SE additional fledging per 10,000 m² of optimal foraging habitat within 300m of the nest).

DISCUSSION

Habitat selection in breeding choughs

Thanks to the accurate modelling of foraging areas using standardized data from focal sampling of feeding choughs, it was possible to estimate which habitats were preferentially used by choughs when foraging. Maritime turf appeared to be the most selected feeding habitat, whereas heathland and coastal ungrazed grassland were clearly avoided, as found in previous studies of coastal populations [START_REF] Bignal | Feeding behavior of nestling choughs in the Scottish Hebrides[END_REF], Bullock et al. 1983[START_REF] Meyer | Observations on two red-billed choughs Pyrrhocorax pyrrocorax in Corwall: habitat use and food intake[END_REF][START_REF] Roberston | Habitat selection and foraging behaviour of breeding choughs Pyrrhocorax pyrrhocorax L. in county Donegal[END_REF], Whitehead et al. 2005). Footpaths could appear as a quantitatively minor feeding habitat, though it was strongly selected according to their availability, as observed by Whitehead et al. (2005). However, the low frequency of choughs seen feeding in pasture on Ouessant strongly contrasts with what is observed elsewhere, as it is generally cited in previous studies, that the major feeding habitat for chough is agricultural land devoted to low-intensity grazing [START_REF] Garcia-Dory | Datos sobre la ecologia del genero Pyrrhocorax (P. pyrrhocorax y P. graculus) en el parque Nacional de la Montana de Covodonga[END_REF][START_REF] Meyer | The diet of the chough Pyrrhocorax pyrrhocorax as indicated by analysis of digested prey remains[END_REF][START_REF] Mcklay | Chough, habitat and land use on islay[END_REF][START_REF] Bignal | Long term studies of social organisation and behaviour[END_REF]. Habitats preferred by feeding choughs on Ouessant are characterized by a mean sward height lower that 5cm, whereas habitat with taller vegetation are avoided. Habitat attractiveness is known to decrease when the height of the vegetation increases and selectivity coefficient for sward height became null or negative beyond 10cm (Whitehead et al. 2005). This could explain why Ouessant pastures, submitted to a very low grazing pressure (mean 266kg of life grazing animals / ha in 2002), are avoided, as vegetation height in pastures ranges from 10 to 40cm. Few data were previously available about home-range size of choughs, though there were some information on maximum distances between main feeding areas and nests. Indeed, Whitehead et al. (2005) found a similar decreasing frequency of habitat use with distance from the nest in a Welsh population, where choughs foraged mostly in habitats within 300m of the nest, with observations further than one kilometre from the nest being rare.

Territory quality and fledging success.

Fledging success was positively related to the amount of feeding habitat and negatively to the distance between such habitats and nest. Yearly changes in territory quality as observed for some pairs were likely due to changes in the local social interactions, such as the disappearance of a breeding pair and the consequent appropriation of its former territory by a neighbouring pair. Another awkward consequence of feeding far from the nest is the decrease in nest guarding against predators such as crow (Corvus corone). Indeed, complete nest failure, presumably due to depredation, adjusted to nest and year could be in part correlated to mean feeding distance (Fbinomial1,44=25.5, Chisq=0.06).

Conservation implication

Ouessant has undergone a fallowing land due to progressive abandonment of agro-pastoral practices. This inevitably led to development of unsuitable foraging vegetation covers for choughs, like scrubs and brambles. Nowadays, such bushy open areas cover more than half of the island area. Moreover, most ancient pastures are under-grazed and become long-grass lands, which are also avoided by feeding choughs. Optimal feeding habitats are now spatially limited to remnant coastal vegetation, maintained by maritime environmental constraints or localised in areas trampled by tourist. Agricultural abandonment has directly reduced the quantity and quality of suitable habitat and probably partly explains the lower fledging success recorded at Ouessant when compared to other study sites (Table 3). Indirectly, abandonment has also promoted predator installation. As an example, the Carrion Crow did not nest on Ouessant before 1971, because of the lack of bushes and trees for potential breeders. From the first breeding pairs in 1971, 30 pairs were breeding on the island in 1984 and about 50 pairs in 2002. Habitat loss, increasing predation risks but also tourism disturbance threatened the chough population, especially through decrease of young survival, to the point where this population short -term viability is concerned (Kerbiriou et al in prep.).

All these elements point towards the urgent need to apply landscape management in order to maintain this core population of chough in Western France.

To define suitable management measures to be undertaken, we needed to identify the demographic determinants of population growth rate. On the chough population of Islay (Scotland) [START_REF] Reid | Identifying the demographic determinants of population growth rate : a case study of red-billed choughs Pyrrhocorax pyrrhocorax[END_REF] have evaluate the percentage of contribution of between-year variation in first-year, second year and adult survival and mean breeding success to total variance of population growth rate. This long-term study show thethree survivals parameters contributed each to 25 % of total variance in population growth rate whereas mean breeding success contribute only for 15%. Even if breeding success is not the main factor constraining population growth rate, from a conservation management point of view it would certainly be more easy to make appropriate landscape management measures aiming at an increase in breeding success, rather than an increase in survival.

The amount of suitable feeding habitat next to the nest is a key factor affecting fledging success. Hence, our results allow us to suggest, optimise and establish a scale of priority for future management efforts. The first priorities consist in stopping on going fallow land process and soil erosion (due to heavy tourist trampling around breeding sites). Next, the restoration of short vegetation through mowing or livestock grazing must be planned close to known active nests, especially in a 300m radius circles from the nests. Each additional 10,000 m² of suitable vegetation in this neighbouring area should allow to add one more young to the fledging family. Because of nest-site shortage, we recommend focusing on site with weak average productivity. (for example, in 8 years of survey two breeding sites have produced respectively 0 and 1 young but have been occupied 7 years). Finally, we can also consider the restoration of short vegetation on historical and potential new breeding sites.

ACKNOLEDGEMENTS

Special thanks are due to Jacques Nisser who helped with defining the ringing techniques and Hélène Pouliquen f or is help with English language. In addition we wish to thank the following for their participation in breeding chough survey sessions : A. Audevard, R. Baeta, C. Caïn, B. Combot, C. Constantin, R. Couix, N. Le Clainc'h, A. Guillaume, P. Laurent, V. Le Pe nnec, R. Morin, G. Ruiz, S. Tessier and L. Therin. We thank two anonymous referees for comments on earlier drafts of this manuscript. Area (m²) of short habitat in 300m buffer

Fledgings

APPENDIX I

We tested whether modelled foraging area size was sensitive to the number of sampling sessions we made in the field. To do this, we used data from four that were surveyed on nine occasions in 1998. We randomly chose 2 to 8 sessions within the available pool of 9, performed the foraging area analyses to determine how many sampling sessions were necessary to obtain unbiased foraging area size estimates. When considering 2 to 5 sessions, we made 20 random permutations within the 9 sessions, 10 when considering 6 to 7 sessions and the 8 possible permutations for 8 sessions. Curve stabilisation could be observed from 4 sessions onwards for three nest, and from 3 sessions for the remaining one(Fig. i).

ANOVA analysis of foraging area size as a function of nest identity and of the number of survey indicated a significant correlation between foraging area size and number of survey until 4 (Table i.), whereas from 5 to 9 sampling no significant correlation could be detected (Table i).

For these four territories, foraging area size estimated after 4 sessions was c.a. 90% of the foraging area obtained with the full set of 9 sessions. Therefore, we further modelled foraging areas sizes only for breeding pairs surveyed at least at 4 occasions. For the few breeding pairs with more than 4 survey sessions available, spare sessions were eliminated from the analysis with the following criteria: session with an effective observation lasting less than 1h30, or date far from the core reproductive period.

Figure 3 .

 3 Figure 3. Two examples of territory change dark circle are localisation of nest and dark grey areas represent suitable chough habitat.(a) The breeding pair P19 settled on the abandoned territory (O22) an thus reduced its long distance feeding trip. (b) Dominant behaviour between two sites had changed : B22 pairs in 1998 had a dominant behaviour status and therefore occupied the majority of the suitable habitat expelling the C23 pair and then forcing this pairs to feed most of the time far away from its nest. In 2003 the dominant behaviour status was inverted and so were territories patterns.

Figure 4 .

 4 Figure 4. Relationship between territory quality and fledging success.

Figure i .

 i Figure i. Relationship between estimated home ranges and number of survey sessions considered, () nest V11, () nest P19, () nest F19 and () nest I11. Same nests as those figured in fig.1.

Table 1 .

 1 Classification of coastal habitats used by chough.

	Habitat class Vegetation structure and composition
	Rocky and	vegetation with many rocky outcrops under 5 cm high, dominated by Armeria
	short	maritima, Plantago coronopus, Festuca rubra pruinosa, Sedum anglicum,
	grassland	Jasione montana, lichen (Cladonia sp), and also a large part of annual species
	Short	vegetation with a total covering and under 5 cm high, dominated by Plantago
	grassland	coronopus, Festuca rubra pruinosa, Agrostis stolonifera maritima,
		Chamamelum nobile, Scilla verna, Centaurium erythraea
	Path	vegetation under 5 cm high, created by human use and dominated by Plantago
		coronopus, Festuca rubra, Bellis perennis, Lolium perenne, Agrostis tenuis,
		Cynosurus cristatus
	Short	vegetation height included between 5 cm and 15 cm and dominated by Erica
	heathland	cinerea, Calluna vulgaris, Danthonia decumbens, Pedicularis sylvatica,
		Thymus drucei
	Littoral	vegetation height included between 5 cm and 15 cm and dominated by Festuca
	grassland	rubra pruinosa, Agrostis stolonifera maritima, Holcus lanatus, Plantago
		lanceolata, Daucus carota gummifer, Lotus corniculatus, Silene maritima
	Pasture	vegetation grazed by sheep, but with a low pressure of grazing, height included
		between 10 cm and 40 cm and dominated by Dactylis glomerata, Holcus
		lanatus, Trifolium repens, Lolium perenne
	Medium	vegetation height included between 15 cm and 50 cm and dominated by Erica
	heathland	cinerea , Calluna vulgaris, Ulex gallii
	Vegetation	vegetation under management operation, is at least mowed twice annually. This
	in restoration	vegetation height range from 5 cm to 50cm. This vegetation is dominated by
		fallow land species (Pteridium aquilinum, Rubus sp, Dactylis glomerata, Ulex
		europaeus). Progressively changing to grassland species (Dactylis glomerata,
		Holcus lanatus, Anthoxantum odoratum, Trifolium repens) as management
		proceed.

Table 2 .

 2 Modelling fledging success. Model c, d, e are adjust to nest-site and year, but are not adjust between them.

	Model

Table 3 .

 3 Variations in breeding success of choughs in different West European populations. Examples of four modelled chough breeding territories. Logit index with standard error of habitat selection by feeding chough. PAT : path, RS : Rocky and short grassland, SG : Short grassland, VR : Vegetation in restoration, SH : Short heathland, LG : littoral grassland, PAS : Pasture, MH : Medium heathland.

	Region	Fledging success of	Fledging success of	n
		the whole population	successful breeder

Table i .

 i Sensitivity of territory size to number of survey.

	Number of survey	F Value	Pr
	1-9	F1,469 = 137.2	Pr > 0.0001
	2-9	F1,433 = 78.4	Pr > 0.0001
	3-9	F1,353 = 23.7	Pr > 0.0001
	4-9	F1,272 = 4.3	Pr > 0.05
	5-9	F1,192 = 1.6	NS