Aymeric Fromant
email: afromant@deakin.edu.au

Karine Delord

Charles-André Bost

Yonina H Eizenberg

Jonathan A Botha

Yves Cherel

Paco Bustamante

Brett R Gardner

Maud Brault-Favrou

Arnaud Lec'hvien

John P Y Arnould

Impact of extreme environmental conditions: foraging behaviour and trophic ecology responses of a diving seabird, the common diving petrel

Keywords: marine heatwave, Pelecanoides urinatrix, inter-annual variation, GPS tracking, stable isotopes, habitat modelling

The reproductive success of birds is strongly driven by environmental conditions at different time scales. Thus, during periods of low food availability, breeding success is constrained by the ability of adults to adapt their foraging effort and feeding behaviour to maintain regular incubation shifts and chick provisioning. However, while large seabirds can buffer disruptions in prey availability, the ecophysiological constraints of smaller species may limit their behavioural flexibility. By combining information on at-sea movements, foraging habitat, trophic niche, and breeding success, this study evaluated the effects of intense variability in oceanographic conditions on common diving petrels (Pelecanoides urinatrix) at the northern extent of their range in southeastern Australia during four consecutive breeding seasons. Unusually low breeding success (6 and 0%) was observed during two years with intense heatwave events, which were associated with higher foraging effort (foraging trips twice longer) and a substantial shift in trophic niche (lower blood δ 15 N values). These findings suggest that common diving petrels in Bass Strait may have reached a critical threshold above which buffering the effects of environmental variability on their reproductive output is not possible. The clear cascading impacts that marine heatwaves have on zooplankton feeders illustrate the profound bottom-up effect induced by such extreme environmental variations, and suggest strong impact on higher-trophic levels. The wide, circumpolar breeding distribution of the common diving petrel, and its high sensitivity to variations in oceanographic conditions, suggest that this species may be a suitable model to study short-term and long-term behavioural responses to the effects of climate change throughout the Southern Ocean.

Introduction

Seabirds forage in a patchy and dynamic environment where prey is unevenly distributed [START_REF] Hunt | The pelagic distribution of marine birds in a heterogeneous environment[END_REF][START_REF] Weimerskirch | Are seabirds foraging for unpredictable resources?[END_REF]. The variation in physical characteristics of the ocean such as temperature, salinity or currents, strongly influence the distribution and availability of prey which, in turn, determine the foraging behaviour of consumers [START_REF] Franks | Phytoplankton blooms at fronts: patterns, scales, and physical forcing mechanisms[END_REF]). Individuals must be flexible in their foraging behaviour and diet, according to spatio-temporal variations in the abundance and distribution of prey species. Thus, seabirds should adapt their strategy at different time scales (i.e. daily, seasonally or annually) to ensure survival and maximise reproductive output [START_REF] Haury | Patterns and processes in the time-space scales of plankton distributions[END_REF][START_REF] Weimerskirch | Foraging strategy of wandering albatrosses through the breeding season: a study using satellite telemetry[END_REF]). However, climate change is likely to challenge species, as the anticipated increased alterations in the distribution, abundance and diversity of prey should affect their capacity to cope with environmental variability [START_REF] Chambers | Observed and predicted effects of climate on Australian seabirds[END_REF].

Seabirds have been extensively used as ecological indicators of the impacts of environmental variations (Cairn 1992, Piatt et al. 2007[START_REF] Bost | Monitoring prey availability via data loggers deployed on seabirds: advances and present limitations[END_REF]. During periods of low prey abundance, breeding seabirds can adjust their behaviour by increasing their foraging effort and/or adapting their diet [START_REF] Harding | Prey density and the behavioural flexibility of a marine predator: the common murre (Uria aalge)[END_REF][START_REF] Cohen | Changes in prey availability impact the foraging behaviour and fitness of Cape gannets over decade[END_REF]). However, behavioural plasticity varies greatly between species and/or populations [START_REF] Gilmour | Plasticity of foraging behaviors in response to diverse environmental conditions[END_REF], and seabirds with less flexible foraging strategies or capabilities may not cope with drastic environmental variability [START_REF] Quillfeldt | Impacts of climate variation and potential effects of climate change on South American seabirdsa review[END_REF][START_REF] Jakubas | Flexibility of little auks foraging in various oceanographic features in a changing Arctic[END_REF]). Due to their relatively easier access for data collection, the majority of studies have focused on large iconic species, resulting in knowledge being mostly restricted to species of higher trophic level, broad diet and/or large foraging range [START_REF] Chiaradia | Changes in diet and trophic position of a top predator ten years after a mass mortality of a key prey[END_REF][START_REF] Price | Climate variability and breeding parameters of a transhemispheric migratory seabird over seven decades[END_REF]. Consequently, our understanding of the links between seabird parameters and variation in oceanographic conditions is limited [START_REF] Grémillet | Shifts in phenotypic plasticity constrain the value of seabirds as ecological indicators of marine ecosystems[END_REF], with little information available for species feeding locally on low trophic level prey. This is exemplified by small pursuit-diving seabirds with high flight costs that might be less able to buffer the consequences of reduced prey availability and longer foraging trips (Elliott et al. 2013). While significant advances have been made in recent years for small Northern Hemisphere alcids (e.g. [START_REF] Grémillet | Little auks buffer the impact of current Arctic climate change[END_REF][START_REF] Amélineau | Arctic climate change and pollution impact little auk foraging and fitness across a decade[END_REF][START_REF] Jakubas | Flexibility of little auks foraging in various oceanographic features in a changing Arctic[END_REF], information on the at-sea movements and foraging behaviour of Southern Hemisphere diving petrels (Procellaridae), and their capacity to adapt, is deficient [START_REF] Chastel | Body condition and seabird reproductive performance: a study of three petrel species[END_REF][START_REF] Cherel | Seabird year-round and historical feeding ecology: blood and feather  13 C and  15 N values document foraging plasticity of small sympatric petrels[END_REF]. This is of concern considering the wide distribution and large biomass the species comprises [START_REF] Marchant | Handbook of Australian[END_REF]. For example, the common diving petrel (Pelecanoides urniatrix, study species) is a ubiquitous species of the Southern Ocean estimated to 20-30 million individuals (conservative estimation based on the estimated breeding pairs; [START_REF] Marchant | Handbook of Australian[END_REF][START_REF] De | The food consumption of the world's seabirds[END_REF]) and contributing to 600-900,000 tonnes of crustacean biomass consumption annually (estimation based on the average consumption per individual; [START_REF] Guinet | Consumption of marine resources by seabirds and seals in Crozet and Kerguelen waters: changes in relation to consumer biomass 1962-85[END_REF].

During the breeding season, common diving petrels exhibit a unimodal foraging trip duration strategy. This contrasts with most of the other small Procellariiformes that display a dual foraging strategy by alternating short and long foraging trips [START_REF] Weimerskirch | Alternate long and short foraging trips in pelagic seabird parents[END_REF][START_REF] Chastel | Body condition and seabird reproductive performance: a study of three petrel species[END_REF]. Across its wide distribution encompassing different environmental conditions, the common diving petrel consistently does short daily trips, during both the incubation [START_REF] Navarro | Ecological segregation in space, time and trophic niche of sympatric planktivorous petrels[END_REF], Zhang et al. 2018[START_REF] Dunphy | Seabirds as environmental indicators: foraging behaviour and ecophysiology of common diving petrels (Pelecanoides urinatrix) reflect local-scale differences in prey availability[END_REF]) and chick-rearing periods [START_REF] Roby | Chick feeding in the diving petrels Pelecanoides georgicus and P. urinatrix exsul[END_REF][START_REF] Weimerskirch | Alternate long and short foraging trips in pelagic seabird parents[END_REF], Fromant et al. 2020a). This consistent behavioural pattern between populations and across breeding stages could highlight a very high efficiency in foraging and illustrate the species adaptation capacity to different local environments. Conversely, this could indicate a low behavioural plasticity resulting in common diving petrels breeding only where this unimodal foraging behaviour can persist.

Throughout the species range, common diving petrels show differences in breeding phenology (Fromant et al. 2020b), diet [START_REF] Reid | Diet and feeding ecology of the diving petrels Pelecanoides georgicus and P. urinatrix at South Georgia[END_REF][START_REF] Bocher | Complete trophic segregation between South Georgian and common diving petrels during breeding at Iles Kerguelen[END_REF], Fromant et al. 2020c) and diving behaviour [START_REF] Bocher | Complete trophic segregation between South Georgian and common diving petrels during breeding at Iles Kerguelen[END_REF], Navarro et al. 2014[START_REF] Dunphy | Comparative seabird diving physiology: first measures of haematological parameters and oxygen stores in three New Zealand Procellariiformes[END_REF], showing how populations adapt to specific conditions. However, it is uncertain if these variations demonstrate behavioural flexibility at the species and/or population level. In particular, the absence of combined multi-year datasets on the trophic and foraging behaviour at a given locality impedes our understanding of how small, abundant seabirds such as diving petrels adapt to inter-annual environmental changes.

Despite its relatively low primary productivity, Bass Strait, the shallow (50-100 m) continental shelf area between mainland Australia and Tasmania, hosts 60% of Australian seabirds [START_REF] Ross | The status of Australia's seabirds[END_REF]. Currents within Bass Strait are complex and dynamic, fluctuating spatially, seasonally and annually, and being influenced by tides, winds and density-driven flows [START_REF] Sandery | Transport timescales for identifying seasonal variation in Bass Strait, south-eastern Australia[END_REF]. This region is also one of the most rapidly changing areas of the global ocean, characterised by warming waters and changing currents [START_REF] Cai | The response of the Southern Annular Mode, the East Australian Current, and the southern mid-latitude ocean circulation to global warming[END_REF][START_REF] Poloczanska | Climate change and Australian marine life[END_REF]).

These ongoing changes are likely to deeply influence the abundance and distribution of cold water zooplanktonic communities [START_REF] Evans | Significant shifts in coastal zooplankton populations through the 2015/16 Tasman Sea marine heatwave[END_REF], and could potentially affect zooplanktivorous species such as common diving petrels [START_REF] Chambers | Observed and predicted effects of climate on Australian seabirds[END_REF][START_REF] Evans | Predicting the distribution of foraging seabirds during a period of heightened environmental variability[END_REF]. In particular, coastal krill (Nyctiphanes australis), the main prey of common diving petrel in Bass Strait [START_REF] Schumann | Diet of common diving-petrels (Pelecanoides urinatrix urinatrix) in southeastern Australia during chick rearing[END_REF], Fromant et al. 2020c), exhibits high sensitivity to increased ocean temperatures [START_REF] Young | Seasonal and interannual variability in krill (Nyctiphanes australis) stocks and their relationship to the fishery for jack mackerel (Trachurus declivis) off eastern Tasmania, Australia[END_REF][START_REF] Mills | The impact of climate fluctuation on food availability and reproductive performance of the planktivorous red-billed gull Larus novaehollandiae scopulinus[END_REF]. Furthermore, Bass Strait represents the northern extent of the common diving petrel range, and the predicted modification of oceanographic parameters in the region are likely to have a profound effect on this small and geographically isolated population [START_REF] Schumann | The significance of northern-central Bass Strait in south-eastern Australia as habitat for burrowing seabirds[END_REF]. Exploring the foraging and trophic ecology of common diving petrels in such a challenging environment will provide valuable information on the extent of its behavioural flexibility and contribute to our understanding of the capacity of small planktonic feeders to buffer contrasted environmental fluctuations.

The present study was conducted over four consecutive years on common diving petrels breeding in Bass Strait. Its aims were to determine: (1) their at-sea movements and habitat use; (2) trophic niche; and 3) inter-annual variation in relation to environmental parameters and reproductive output. Specifically, south-eastern Australia experienced over the last decade successive intense summer marine heatwaves (prolonged periods where ocean temperatures are above the climatological average; [START_REF] Oliver | The unprecedented 2015/16 Tasman Sea marine heatwave[END_REF], Perkins-Kirkpatrick et al. 2019). If these extreme rises in sea surface temperature induce major shifts in zooplankton population structure [START_REF] Evans | Significant shifts in coastal zooplankton populations through the 2015/16 Tasman Sea marine heatwave[END_REF], the cascading effect that marine heatwaves have on upper trophic levels remains unknown. We predicted that (1) diving petrel trip duration and foraging area would increase in response to the negative effect of marine heatwaves on cold-water zooplanktonic prey;

(2) the shifts in prey availability would induce a modification in the birds' trophic niche; and (3) the resultant increased in foraging effort would negatively impacts their breeding success.

Materials and Methods

Study site and animal instrumentation

The study was conducted during the incubation and chick-rearing periods over four consecutive years (2017-2020) on Kanowna Island (39°15'S 146°30'E) in northern Bass Strait, south-eastern Australia. This island is a breeding site for seven seabird species (Fromant et al. 2020d), including 250-500 pairs of common diving petrels (2-4% of the northern Bass Strait population; [START_REF] Schumann | The significance of northern-central Bass Strait in south-eastern Australia as habitat for burrowing seabirds[END_REF]. Some study nests (20-30 per year) were randomly located at the start of each breeding season to record the birds' phenology. Control nests (2017: 16;2018: 66;2019: 63;2020: 46) were monitored in early incubation, post-hatching and before fledging to calculate the average reproductive success for the colony (hatching, fledging and breeding success). In addition, during chick-rearing in 2017, burrows (n = 40) were monitored weekly in order to estimate the potential effects of short-term deployments of miniaturized devices on adult body mass, chick growth and breeding success (see Supplementary text; Table S1).

To evaluate the at-sea distribution of common diving petrels during the breeding period, adult breeding birds were equipped with miniature GPS data loggers (nanoFix-GEO, Pathtrack Ltd, Otley, United-Kingdom), attached to two tail feathers using waterproof tape (Tesa 4651;

Beiersdorf AG). The total mass of the devices corresponded to 2.25 ± 0.18% of body mass (134 ± 11 g) and, thus, was unlikely to have impacted the feeding ecology or breeding performance of individuals (see Supplementary text). During incubation, both partners alternate between 1 d foraging at sea and 1 d incubating [START_REF] Weimerskirch | Alternate long and short foraging trips in pelagic seabird parents[END_REF], Zhang et al. 2018), while during chick-rearing (post-brooding stage), both individuals forage at sea during the day and come back to the nest every night to feed the chick [START_REF] Marchant | Handbook of Australian[END_REF]. Accordingly, during incubation, the study birds were captured in their burrow in the afternoon (corresponding to the end of their shifts) while during the chick-rearing period they were captured at night after feeding the chick.

When individuals were recaptured, a blood sample (0.2 mL) was collected from the brachial vein for stable isotope analyses and sexing. For all birds, sex was determined by DNA analysis (DNA solutions, Wantirna South, Australia) from either blood or a single body feather. Individuals were weighed (± 2 g; Pesola), and culmen, tarsus (± 0.1 mm; Vernier calipers) and wing length (± 1 mm; ruler) were measured. Handling time at deployment (banding, weighing and device attachment) and recapture (device removal, measurements, blood and feather sampling) was usually less than 5 min.

Environmental data and habitat selection modelling

Environmental data were used to run two distinct sets of analysis: (1) using sea surface temperature (SST) to explore the variation in foraging ecology and breeding outputs of common diving petrels following summer marine heatwave events. Hereafter, a marine heatwave event is defined as daily SST above the seasonally varying 90 th percentile (climatological mean for the period 1981-2010) for more than 5 consecutive days [START_REF] Oliver | The unprecedented 2015/16 Tasman Sea marine heatwave[END_REF][START_REF] Oliver | Marine heatwaves[END_REF]; (2) using dynamic environmental covariates (see details in section 2.2.2.) to describe the habitat selection and determining the physical features explaining the foraging distribution of breeding common diving petrels in Bass Strait.

Inter-annual variations of oceanographic conditions

Sea surface temperature has been shown to be the main feature influencing the occurrence and abundance of zooplankton species in south-eastern Australia [START_REF] Evans | Significant shifts in coastal zooplankton populations through the 2015/16 Tasman Sea marine heatwave[END_REF][START_REF] Evans | Predicting the distribution of foraging seabirds during a period of heightened environmental variability[END_REF]. In particular, the distribution and availability of coastal krill, the main common diving petrel prey in Bass Strait [START_REF] Schumann | Diet of common diving-petrels (Pelecanoides urinatrix urinatrix) in southeastern Australia during chick rearing[END_REF], Fromant et al. 2020c), vary substantially between years in relation to SST [START_REF] Young | Seasonal and interannual variability in krill (Nyctiphanes australis) stocks and their relationship to the fishery for jack mackerel (Trachurus declivis) off eastern Tasmania, Australia[END_REF][START_REF] Mills | The impact of climate fluctuation on food availability and reproductive performance of the planktivorous red-billed gull Larus novaehollandiae scopulinus[END_REF].

Specifically, summer marine heatwaves with prolonged period of SST above the optimal temperature range of coastal krill (12-18 °C;[START_REF] Sheard | Taxonomy, distribution, and development of Euphausiacea (Crustacea). Report of British Australian and New Zealand Antarctic Research Expedition Series B[END_REF] alter the reproduction, survival, and potentially disrupt the availability of this key planktonic species for several months [START_REF] Ritz | Production of the euphausiid Nyctiphanes australis in Storm Bay, south-eastern Tasmania[END_REF][START_REF] O'brien | Surface schooling behaviour of the coastal krill Nyctiphanes australis (Crustacea: Euphausiacea) off Tasmania, Australia[END_REF]. Therefore, for each summer, the duration and intensity of periods strictly above the optimal temperature range of coastal krill (>19 °C ;[START_REF] Sheard | Taxonomy, distribution, and development of Euphausiacea (Crustacea). Report of British Australian and New Zealand Antarctic Research Expedition Series B[END_REF]

Habitat selection modelling

To investigate the influence of environmental variables on the at-sea movements and foraging behavior of breeding common diving petrels, habitat selection in relation to habitat availability was determined using a presence-pseudoabsence approach in R software (Hindell et al. 2020[START_REF] Core | R: a Language and Environment for Statistical Computing R Foundation for Statistical Computing[END_REF]. Specifically, for each real track (n = 187), 20 pseudo-tracks were simulated by means of a first-order vector autoregressive model fitted using the package availability [START_REF] Raymond | Availability: estimating geographic space available to animals based on telemetry data[END_REF]. Simulations were created with constraints on sampling frequency, distances, turning angles and departure/arrival locations to maintain the characteristics of the real tracks. Furthermore, pseudo-tracks were bound by a land mask to ensure that all simulated locations were at sea.

Ten dynamic environmental covariates that have been shown to potentially influence marine predators and their habitat use [START_REF] Reisinger | Habitat modelling of tracking data from multiple marine predators identifies important areas in the Southern Indian Ocean[END_REF], Hindell et al. 2020)

𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑠𝑝𝑒𝑒𝑑 = √𝑛𝑜𝑟𝑡ℎ𝑤𝑎𝑟𝑑 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 2 + 𝑒𝑎𝑠𝑡𝑤𝑎𝑟𝑑 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 2
In addition, bathymetric data were downloaded from the GEBCO 15-arc second grid

[http://www.gebco.net] and used to calculate sea floor slope by means of the terrain function from the raster package. Given that environmental covariates differed substantially in resolution (0.004 to 0.083º), all layers were standardized to the coarsest resolution (0.083º) and spatiotemporally matched to each real and pseudo-location using the raster package [START_REF] Hijmans | Raster: geographic data analysis and modeling[END_REF]). Dynamic covariates were averaged for the duration of each track before being matched to each location.

Tracking and stable isotope processing and analysis

Tracking and spatial analysis

The GPS data loggers were programmed with a sampling interval of 10 and 5 min during the incubation and chick-rearing periods, respectively. Prior to analysis, land-based points were removed and a speed filter with a threshold at 20 m•s -1 was applied to remove erroneous locations [START_REF] Spear | Flight behaviour of seabirds in relation to wind direction and wing morphology[END_REF]. Because of poor satellite reception during intense diving activity, linear interpolation was necessary to correct for unequal sampling frequencies between foraging and commuting periods. For each complete trip (1-7 per individual bird) the following basic parameters were calculated: 1) time of departure and return; 2) trip duration; 3) total horizontal distance travelled; 4) maximum distance from the colony; and 5) bearing at departure and distal location.

For heavily wing-loaded species such as diving petrels, alcids or cormorants, typical foraging trips consist of departing from the colony rapidly with a constant bearing to a particular area for foraging, and returning in a direct flight path to the colony [START_REF] Weimerskirch | Are seabirds foraging for unpredictable resources?[END_REF][START_REF] Amélineau | Where to forage in the absence of sea ice? Bathymetry as a key factor for an Arctic seabird[END_REF]. Diving petrels forage by diving from the sea surface, which impedes the distinction between foraging and resting behaviors when using GPS only. Foraging/resting (hereafter foraging) areas were defined as areas were instantaneous speed was ≤ 10 km•h -1 , following the method previously used on ecologically similar species (e.g. [START_REF] Amélineau | Where to forage in the absence of sea ice? Bathymetry as a key factor for an Arctic seabird[END_REF][START_REF] Jakubas | Flexibility of little auks foraging in various oceanographic features in a changing Arctic[END_REF]. The remaining positions (speeds > 10 km•h -1 ) were assumed to represent flying between the colony and the foraging areas or between two feeding areas. In the analysis of the relationship between the proportion of time spent foraging and the total distance travelled, 1 d trips and 2 d trips were analyzed separately in order to discount the effect of staying at-sea overnight (3 d trips were not included because of the low sample size). Indeed, in the case of an at-sea overnight stay (common diving petrels do not forage at night; [START_REF] Navarro | Ecological segregation in space, time and trophic niche of sympatric planktivorous petrels[END_REF], the absence of commuting to the colony at the end of the first day, and from the colony at the start of the second day, up weights the proportion of time spent foraging compared to commuting.

Locations identified as foraging were used to generate kernel utilization distribution (UD) estimates using the package adehabitatLT [START_REF] Calenge | The package adehabitat for the R software: a tool for the analysis of space and habitat use by animals[END_REF]. For each year and breeding stage, the 50% (core foraging area) and 95% (home range) kernel UD contours were obtained [START_REF] Worton | Kernel methods for estimating the utilization distribution in home-range studies[END_REF][START_REF] Montevecchi | Tracking seabirds to identify ecologically important and high risk marine areas in the western North Atlantic[END_REF]. To investigate spatial variation in foraging area, the percentage overlap in foraging distribution between years and breeding stages were estimated using Bhattacharyya's affinity (BA), where 0 indicates no overlap and 1 a complete overlap.

Isotopic niche analysis

Stable isotope analyses of carbon (δ 13 C) and nitrogen (δ 15 N) in whole blood were used to investigate temporal change in the common diving petrel trophic niche, reflecting dietary integration of approximately two to four weeks [START_REF] Bearhop | Factors that influence assimilation rates and fractionation of nitrogen and carbon stable isotopes in avian blood and feathers[END_REF]. Prior to analyses, samples were freeze-dried, ground to powder and homogenized. The relative abundance of carbon and nitrogen isotopes was determined with a continuous-flow mass spectrometer (Thermo Scientific Delta V Advantage) coupled to an elemental analyser (Thermo Scientific Flash EA 1112). Isotopic results are presented in the δ notation relative to Vienna PeeBee Belemnite and atmospheric N2 for δ 13 C and δ 15 N, respectively. Replicate measurements of internal laboratory standards (acetanilide)

indicate measurement errors <0.10 ‰ for both δ 13 C and δ 15 N values. The C:N mass ratios of samples were calculated as the ratio between the mass percentages in carbon and nitrogen. The consistently low C:N values of blood (<4.0) verified that low lipid content did not necessitate lipid extraction (Cherel et al. 2005a). The isotopic niche position and width was compared between years and breeding stages using the ellipse area-based metrics of the SIBER package [START_REF] Jackson | Comparing isotopic niche widths among and within communities: SIBER-Stable Isotope Bayesian Ellipses in R[END_REF]). The isotopic niche was estimated by the 40% standard ellipse area corrected for small sample size (SEAC), the Bayesian standard ellipses areas (SEAB) on 10 5 replicates was used to measure the overlap of the isotopic niches between each breeding stage, and the total area of the convex hull (TA) to provide an indication of the niche width [START_REF] Jackson | Comparing isotopic niche widths among and within communities: SIBER-Stable Isotope Bayesian Ellipses in R[END_REF].

Statistical analyses

To examine seasonal and inter-annual differences in SST, a one-way ANOVA and Tukey's post-hoc analysis were used. Habitat selection was assessed using boosted regression trees (BRT) [START_REF] Friedman | Greedy function approximation: A gradient boosting machine[END_REF] to determine the importance of each environmental covariate on the probability of habitat used in relation to availability. To ensure that individuals contributed equally to the analysis, modelling was restricted to the first foraging trip of each individual. Prior to analysis, collinearity between predictor effects was assessed and, if correlations where > 0.6, the environmental covariate with the highest average correlations was excluded from the model (sea floor temperature, wave height). The BRT were fitted using the dismo package [START_REF] Hijmans | Package dismo[END_REF]) and locations were modelled as a binomial response, where all real locations were represented by 1 and all pseudo-locations were represented by 0. The BRT were fitted with a tree complexity of 5 and total of 6450 trees were fitted at a learning rate of 0.05 [START_REF] Elith | A working guide to boosted regression trees[END_REF].

Model performance was evaluated using 10-fold cross validation and represented by the area under the receiver operating characteristic curve (AUC).

Effects on foraging parameters (i.e. time of departure and return, trip duration, total horizontal distance travelled, maximum distance from the colony, and bearing at departure and distal location) were investigated generating multiple Generalized Linear Mixed Models (GLMM) using the package glmmADMB [START_REF] Bolker | Getting started with the glmmADMB package[END_REF]. Year, breeding stage and sex were considered as fixed effects, and individual was added as a random effect, with a Gaussian family. Models were ranked based on their Akaike's Information Criterion (AIC) and were checked to ensure normality and homoscedasticity of residuals [START_REF] Zuur | A protocol for data exploration to avoid common statistical problems[END_REF]) before further statistical analysis.

Data normality and homogeneity of the variance were assessed with Shapiro-Wilk and Bartlett tests, respectively. Post-hoc analyses were conducted using pairwise comparisons of least-squares means between years, breeding stages and sex (package emmeans; Lenth 2020) with the Tukey method for p-value adjustment. The variation between years and stages in the trip orientation (bearing at departure and at distal location) was investigated by calculating the angular difference (Rao's spacing test, alpha = 0.05; package circular; [START_REF] Lund | circular: Circular Statistics[END_REF]. Differences between years and breeding stages δ 13 C and δ 15 N values were tested by using 2-way semi-parametric permutation multivariate analyses of variance test (PERMANOVA) on the Euclidean distance matrix [START_REF] Anderson | A new method for non-parametric multivariate analysis of variance[END_REF]). Spearman's rank correlation was used to test whether there was a correlation between the proportion of time spent foraging and trip duration. Hatching success (eggs hatched as a proportion of eggs laid), fledging success (chicks fledged as a proportion of eggs hatched) and breeding success (chicks fledged as a proportion of eggs laid) were compared between years using a Pearson's chi-squared test. All statistical analyses were conducted in the R statistical environment 4.0.0 (R Core Team 2020).

Results

Environmental variables and habitat selection

Inter-annual variations of oceanographic conditions

During the whole study period, SST varied strongly, ranging from 10.9 to 21.5 ºC, exhibiting an annual cycle with significant differences between the seasons (ANOVA, F641.1 = 69.925, P < 0.001), and significant inter-annual variations (ANOVA, F197.63 = 58.194, P < 0.001).

Importantly, the average temperature in summer preceding the common diving petrel breeding season in 2018 (18.5 ± 0.9 °C) and 2019 (18.2 ± 1.1 °C) were significantly warmer than in 2017

Habitat selection modelling

The final BRT model returned an AUC score of 0.96 ± 0.01 and identified salinity, wave direction and SST as the most important factors for predicting habitat selection (Table 1;

Fig. S1). Salinity had a variable relative influence of 18.4%, with fitted functions indicating that the probability of habitat selection decreased with increasing salinity. Both wave direction and SST had a lower variable relative influence (12.3% and 11.4%, respectively). For wave direction, fitted functions indicated that the probability of selection was relatively constant, although there were two slight peaks with wave direction from ESE (110°) and WNW (280-300°). For SST, fitted functions indicated that the probability of selection peaked at 12.5 ºC, after which it remained relatively constant (Fig. S1).

The main variables influencing the habitat selection models varied between years and breeding stages (Table 1; Fig. S2). Similarly, the relative influence of each variable differed among the models. Salinity had a high relative influence for all the models except for chickrearing 2018 (7.1%), while sea surface height and SST were significant only in the model for incubation 2019 (Fig. S2).

Foraging parameters and at-sea distribution

At-sea movement data were obtained from a total of 67 trips in incubation (36 individuals) and 122 trips during chick-rearing (65 individuals). Data for both the incubation and chick-rearing periods within the same season were collected in 2018 and 2020. Due to logistical constraints, no data were obtained during incubation in 2017. In 2019, all the study nests failed (young chicks found dead in the burrow) before any birds could be equipped during the chick-rearing period.

There were no significant differences between the sexes (48 females and 53 males) in trip parameters (P > 0.05 in all cases) and, therefore, data from both sexes were pooled in all subsequent statistical analyses.

Foraging parameters and at-sea distribution according to the breeding stage: incubation vs chick rearing

Within the same breeding season (in 2018 and 2020), habitat distribution differed between the incubation and chick-rearing periods (Fig. 2; home ranges during incubation was 42% larger than during chick-rearing in 2018, and 10% in 2020; BAincubation/chick-rearing = 0.26 in 2018 and 0.48 in 2020). In 2018, the total distance travelled was significantly different between the incubation and chick-rearing stages (Table 3; Mann-Whitney U test: U = 483, P = 0.020).

However, no significant differences in the trip parameters were found between the two breeding stages in 2020.

Individuals consistently departed from the colony earlier during incubation than during the chick-rearing period (Table 3; Mann-Whitney U test: U = 6064, P < 0.001), but no clear pattern was observed for the timing of return (Mann-Whitney U test: U = 4758, P = 0.062).

However, the time between departure and sunrise, and the time between sunset and return, were positively correlated to the total distance travelled. The sampling period did not influence the

Foraging parameters and at-sea distribution according to the years

Home range differed inter-annually in size and location during both the incubation and chick-rearing periods (Fig. 2). The home range was the smallest in 2020 during the incubation and chick-rearing periods, and it was the largest in incubation 2019 and chick-rearing 2018.

All parameters of foraging trips varied inter-annually, i.e. in terms of duration, total distance travelled, and maximum distance from the colony (Fig. 2; Table 3; Table S2; Kruskal-Wallis test, P < 0.001 for all parameters).

In incubation, the proportion of foraging trips that were of 1 d duration varied from

Isotopic values for δ 13 C and δ 15 N

Whole blood δ 13 C and δ 15 N values varied substantially between years and breeding stages (Table 4; Fig. 4; PERMANOVA, F5 = 50.81, R 2 = 0.677, P = 0.001; ANOVA, P < 0.001 for both δ 13 C and δ 15 N). This variation was characterized by very limited isotopic niche overlap between stage/year (Table S3), all < 15% except between incubation 2018 and incubation 2019 S3; TA in incubation 2018 = 3.47 and in incubation 2019 = 4.61) than during the 2020 incubation period (TA = 0.21). No such variations were observed during the chick-rearing period (Fig. 4; Table S3). Fromant et al., 2020Fromant et al., (2008, n = 10;, n = 10;2009, n = 4;2010, n = 15). Full lines correspond to the 40% ellipse and dashed lines 100% total convex hull. The blue and red writing represent cold and warm years, respectively (see Figure 1).

(

Discussion

Using a combination of GPS tracking and stable isotope analyses, the present study documented for the first time substantial variations over four successive breeding cycles in the at-sea movements, foraging behaviour and trophic niche of a small planktonic forager, the common diving petrel. The salient features of the results can be summarized as following: i) these inter-annual variations coincided with drastic fluctuations in reproductive success and were associated with intense summer marine heatwave events; ii) during years of low breeding success, common diving petrels strongly increased their foraging effort and shifted their trophic niche, likely in response to important variations in prey availability; iii) the clear cascading effects that marine heatwaves have on the breeding and foraging ecology of this zooplankton feeder (Fig. 5) illustrate the rapid bottom-up effect induced by extreme environmental variations. For species breeding on the edge of their distribution range, the predicted intensification of marine heatwaves is likely to strengthen the detrimental effects on their breeding output. Full red blocks and arrows are results observed in the present study; Dotted red blocks and arrows are adapted from the literature [START_REF] Young | Seasonal and interannual variability in krill (Nyctiphanes australis) stocks and their relationship to the fishery for jack mackerel (Trachurus declivis) off eastern Tasmania, Australia[END_REF], Harding et al. 2007[START_REF] Cohen | Changes in prey availability impact the foraging behaviour and fitness of Cape gannets over decade[END_REF][START_REF] Oliver | The unprecedented 2015/16 Tasman Sea marine heatwave[END_REF][START_REF] Evans | Significant shifts in coastal zooplankton populations through the 2015/16 Tasman Sea marine heatwave[END_REF]) (photo ©: A. Slotwinski and G. Jones)

Foraging behaviour, at-sea distribution and habitat use

In all studied years, the foraging activity of the common diving petrels breeding on Kanowna Island was consistently restricted to the shallow continental shelf of Bass Strait.

Although, diving petrel species seem to appear morphologically better suited for short foraging trips during breeding [START_REF] Navarro | Ecological segregation in space, time and trophic niche of sympatric planktivorous petrels[END_REF], common diving petrels in Bass Strait exhibited relatively long foraging trips (average maximum distance from the colony = 71 ± 3 km) both during the incubation and chick-rearing periods. In all breeding stages and years, the diving petrels from Kanowna Island foraged farther away from the colony and conducted foraging trips 2-6 times longer than conspecifics in New Zealand (Zhang et al. 2018[START_REF] Dunphy | Seabirds as environmental indicators: foraging behaviour and ecophysiology of common diving petrels (Pelecanoides urinatrix) reflect local-scale differences in prey availability[END_REF] and Peruvian diving petrels (Pelecanoides garnotii) in Peru [START_REF] Zavalaga | Foraging movements of Peruvian diving-petrels in Isla La Vieja, Peru[END_REF].

The overall foraging distribution of common diving petrels in the present study was in accordance with at-sea observation of the species in south-eastern Australian waters [START_REF] Reid | Seabird Atlas of South-eastern Australian Waters[END_REF], and matches the habitat distribution of their main prey, i.e. coastal krill [START_REF] O'brien | Surface schooling behaviour of the coastal krill Nyctiphanes australis (Crustacea: Euphausiacea) off Tasmania, Australia[END_REF][START_REF] Schumann | Diet of common diving-petrels (Pelecanoides urinatrix urinatrix) in southeastern Australia during chick rearing[END_REF]. Blood isotope values in 2017-2020 were within the same range as those previously measured in common diving petrels from the Bass Strait (Fromant et al. 2020c) and New Zealand [START_REF] Dunphy | Seabirds as environmental indicators: foraging behaviour and ecophysiology of common diving petrels (Pelecanoides urinatrix) reflect local-scale differences in prey availability[END_REF]. The average blood δ 15 N value (14.0 ‰) corresponds to one trophic level above the values of coastal krill (δ 15 N = 11.7 ‰; Cherel et al. 2005b), thus confirming the importance of this prey item in the diet of Australian common diving petrels [START_REF] Schumann | Diet of common diving-petrels (Pelecanoides urinatrix urinatrix) in southeastern Australia during chick rearing[END_REF], Fromant et al. 2020c). However, the wide isotopic niche and the large differences in at-sea distribution suggested seasonal and inter-annual prey variation in the diet of diving petrels in Bass Strait, potentially reflecting the complexity of this oceanographic system [START_REF] Sandery | Transport timescales for identifying seasonal variation in Bass Strait, south-eastern Australia[END_REF].

Seabirds increase their foraging efficiency by identifying persistent oceanographic features where prey encountering is predictable [START_REF] Weimerskirch | Are seabirds foraging for unpredictable resources?[END_REF][START_REF] Bost | The importance of oceanographic fronts to marine birds and mammals of the southern oceans[END_REF]). In central Bass Strait, however, the oceanographic processes influencing the productivity are highly spatially and temporally variable [START_REF] Sandery | Transport timescales for identifying seasonal variation in Bass Strait, south-eastern Australia[END_REF][START_REF] Huang | Mapping the spatial and temporal variability of the upwelling systems of the Australian south-eastern coast using 14-year of MODIS data[END_REF]. The higher foraging effort and wide isotopic niche of common diving petrels in Bass Strait could, therefore, be due to the sparse distribution of their prey (O'Brien 1988), leading them to search farther and more widely than other diving petrel populations or similar species [START_REF] Ryan | Foraging behaviour of diving petrels Pelecanoides[END_REF][START_REF] Zavalaga | Foraging movements of Peruvian diving-petrels in Isla La Vieja, Peru[END_REF][START_REF] Dunphy | Seabirds as environmental indicators: foraging behaviour and ecophysiology of common diving petrels (Pelecanoides urinatrix) reflect local-scale differences in prey availability[END_REF]).

Salinity, wave direction and sea surface temperature appeared to be the most meaningful variables to describe the foraging distribution of the common diving petrel in Bass Strait. Higher preference to low salinity and low sea surface temperature is likely to reflect the optimal environmental conditions influencing their prey distribution [START_REF] Sheard | Taxonomy, distribution, and development of Euphausiacea (Crustacea). Report of British Australian and New Zealand Antarctic Research Expedition Series B[END_REF][START_REF] Evans | Significant shifts in coastal zooplankton populations through the 2015/16 Tasman Sea marine heatwave[END_REF]. Such preferences are consistent with distribution models based on at-sea observation of common diving petrels in south-eastern Tasmania, with bird sightings being negatively correlated to SST and salinity [START_REF] Evans | Predicting the distribution of foraging seabirds during a period of heightened environmental variability[END_REF].

However, the important inconsistencies in the habitat selection models between breeding stages and years may suggest a more complex association between potential prey and oceanographic features, and illustrate the oceanographic complexity of the region [START_REF] Sandery | Transport timescales for identifying seasonal variation in Bass Strait, south-eastern Australia[END_REF]. Additionally, the mismatch in resolution between tracking and environmental variables data may have failed to capture the scale at which the phenomenon occurs, impeding our interpretations. A finer resolution should enable in the future to fully understand what parameters influence the at-sea movements of common diving petrels.

Inter-annual variation in breeding success, foraging behaviour and trophic niche

The present study was characterised by two consecutive years of remarkably low breeding success (6% in 2018 and 0% in 2019; [START_REF] Marchant | Handbook of Australian[END_REF][START_REF] Chastel | Body condition and seabird reproductive performance: a study of three petrel species[END_REF].

At Kerguelen, the overall high breeding success of common diving petrels (46-86% over seven years; [START_REF] Chastel | Body condition and seabird reproductive performance: a study of three petrel species[END_REF] suggests that, during years of lower food availability, this species seems to be able to maintain its breeding output by increasing its foraging effort [START_REF] Chastel | Body condition and seabird reproductive performance: a study of three petrel species[END_REF]. However, the same authors concluded that substantial shortage in food availability during the whole breeding season would likely induce an important decrease in breeding success.

In the present study, during years of very low breeding success, common diving petrels exhibited i) a higher distance travelled and lower nest attendance (longer trip duration), and ii)

proportionately less time spent foraging per trip (longer foraging commutes). This higher foraging effort was associated with substantial variation in their isotopic niche (e.g. lower blood δ 15 N values), suggesting a potential dietary shift from rich temperate zooplanktonic species to lower quality subtropical prey [START_REF] Cohen | Changes in prey availability impact the foraging behaviour and fitness of Cape gannets over decade[END_REF][START_REF] Evans | Significant shifts in coastal zooplankton populations through the 2015/16 Tasman Sea marine heatwave[END_REF]. Such adjustments in relation to prey depletion is well documented among seabirds [START_REF] Harding | Prey density and the behavioural flexibility of a marine predator: the common murre (Uria aalge)[END_REF][START_REF] Bost | Large-scale climatic anomalies affect marine predator foraging behaviour and demography[END_REF][START_REF] Barbraud | Density dependence, prey accessibility and prey depletion by fisheries drive Peruvian seabird population dynamics[END_REF]. However, the large decrease in breeding success of common diving petrel in Bass Strait, despite important modification in their foraging effort and trophic niche, underline the magnitude of the apparent disruption in prey availability.

As a key zooplankton species [START_REF] Ritz | Production of the euphausiid Nyctiphanes australis in Storm Bay, south-eastern Tasmania[END_REF], variability in abundance of coastal krill has been observed to influence the foraging behaviour and demographic parameters of various marine predators [START_REF] Mills | The impact of climate fluctuation on food availability and reproductive performance of the planktivorous red-billed gull Larus novaehollandiae scopulinus[END_REF][START_REF] Manno | Buffering against food availability? The physical environment has little influence on breeding performance of fairy prions (Pachyptila turtur)[END_REF]. For example, in New Zealand, delayed breeding period, longer foraging trips and low breeding success of the zooplanktivorous red-billed gull (Larus novaehollandiae scopulinus) were linked to the absence of coastal krill in years of positive sea temperature anomaly [START_REF] Mills | The impact of climate fluctuation on food availability and reproductive performance of the planktivorous red-billed gull Larus novaehollandiae scopulinus[END_REF].

Similarly, in south-eastern Australia, a close relationship has been documented between coastal krill and the capture biomass of barracoota (Thyrsites atun) and jack mackerel (Trachurus declivis) by commercial fisheries, mitigated by the absence of coastal krill during years of high sea temperature anomaly [START_REF] Young | Seasonal and interannual variability in krill (Nyctiphanes australis) stocks and their relationship to the fishery for jack mackerel (Trachurus declivis) off eastern Tasmania, Australia[END_REF]).

In the present study, summers preceding the very low breeding success of common diving petrel (2018 and 2019) were characterized by exceptionally long periods of SST above the optimal temperature range of coastal krill. The abnormal temperature conditions observed during these two successive summers is likely to have altered the availability of this key zooplanktonic species [START_REF] Young | Seasonal and interannual variability in krill (Nyctiphanes australis) stocks and their relationship to the fishery for jack mackerel (Trachurus declivis) off eastern Tasmania, Australia[END_REF][START_REF] Mills | The impact of climate fluctuation on food availability and reproductive performance of the planktivorous red-billed gull Larus novaehollandiae scopulinus[END_REF]. Previous marine heatwaves events in the region resulted in a shift of dominant species from large-bodied cold-water euphausiids to smaller size subtropical copepods [START_REF] Evans | Significant shifts in coastal zooplankton populations through the 2015/16 Tasman Sea marine heatwave[END_REF]. The depletion in the common diving petrel main prey in Bass Strait may have forced individuals to adapt their foraging ecology to prey of lower energetic value. In contrast, the mild SST in summer 2017 (fitting the 1981-2010 average) and the even colder summer 2020 were related to a much higher breeding success (69 and 84%, respectively), indicating prey abundance. The large spectrum of SST observed in this study, within and outside the optimal temperature of coastal krill, therefore, illustrates a strong link between the oceanographic conditions, prey availability and predator breeding success.

The important inter-annual variations in blood isotopic values of common diving petrel (Fromant et al. 2020c, this study) are consistent with a substantial shift in their trophic niche during warmer years (Fig. 1). Alternatively, these variations could result from the spatiotemporal modification in the isotopic baselines in Bass Strait, leading ultimately to fluctuation in the isotopic values of common diving petrel prey [START_REF] Jaeger | Isotopic investigation of contemporary and historic changes in penguin trophic niches and carrying capacity of the Southern Indian Ocean[END_REF][START_REF] Polito | Intraspecific variation in a dominant prey species can bias marine predator dietary estimates derived from stable isotope analysis[END_REF]). However, the large isotopic niche width occupied by common diving petrels in 2018 and 2019 suggests a diversification in their diet, which may indicate a shortage in availability of their main prey following these marine heatwave events [START_REF] Layman | Can stable isotope ratios provide for community-wide measures of trophic structure?[END_REF].

In South-Georgia, the reproductive performance of "krill-dependent" macaroni penguins (Eudyptes chrysolophus) decreased during years of poor Antarctic krill (Euphausia superba) availability [START_REF] Waluda | Diet variability and reproductive performance of macaroni penguins Eudyptes chrysolophus at Bird Island, South Georgia[END_REF]). These years were characterised by a broader diet, which was associated with increased energy and/or time costs. This is consistent with the greater foraging effort and wider isotopic niches observed for the common diving petrel in the present study during years of marine heatwaves. Likewise, in New Zealand, Hutton's shearwaters (Puffinus huttoni) adapted their behaviour by diving significantly deeper during the same marine heatwave events [START_REF] Oliver | The unprecedented 2015/16 Tasman Sea marine heatwave[END_REF], Perkins-Kirkpatrick et al. 2019[START_REF] Bennet | Seasonal and annual variation in the diving behaviour of Hutton's shearwater (Puffinus huttoni)[END_REF].

While the inter-annual variations in foraging ecology of the common diving petrel observed in the present study were concomitant with marine heatwaves in Bass Strait, their underlying mechanisms are poorly understood [START_REF] Perkins-Kirkpatrick | The role of natural variability and anthropogenic climate change in the 2017/18 Tasman Sea marine heatwave[END_REF]. Indeed, the thermal regime of Bass Strait is affected by several climatic and oceanographic features [START_REF] Sandery | Transport timescales for identifying seasonal variation in Bass Strait, south-eastern Australia[END_REF], and further investigations are required to understand the link between environmental conditions, prey availability and the birds feeding and foraging behaviour.

A potentially difficult future for small diving seabirds

Reduction in prey availability during the breeding season in seabirds has been shown

to result in increased foraging effort (e.g. [START_REF] Harding | Prey density and the behavioural flexibility of a marine predator: the common murre (Uria aalge)[END_REF][START_REF] Bost | Large-scale climatic anomalies affect marine predator foraging behaviour and demography[END_REF], lowered adult fitness and survival rate [START_REF] Cohen | Changes in prey availability impact the foraging behaviour and fitness of Cape gannets over decade[END_REF][START_REF] Piatt | Extreme mortality and reproductive failure of common murres resulting from the northeast Pacific marine heatwave of 2014-2016[END_REF], and altered chick growth and breeding success [START_REF] Quillfeldt | Sea surface temperatures and behavioural buffering capacity in thin-billed prions Pachyptila belcheri: breeding success, provisioning and chick begging[END_REF][START_REF] Waluda | Diet variability and reproductive performance of macaroni penguins Eudyptes chrysolophus at Bird Island, South Georgia[END_REF]. Some seabird species can buffer disruptions in prey availability [START_REF] Sommerfeld | Flexible foraging behaviour in a marine predator, the masked booby (Sula dactylatra), according to foraging locations and environmental conditions[END_REF][START_REF] Jakubas | Flexibility of little auks foraging in various oceanographic features in a changing Arctic[END_REF]. However, as central place foragers, the high energetic demands during the breeding season sets a physiological limit that determines the effects of environmental variation on reproductive success and adult survival. The threshold that delineates seabird behavioural flexibility varies greatly among species and ecosystems, and is influenced by factors such as intra-and interspecific competition or geographic constraints.

Modification of zooplankton communities and abundance in marine systems in response to unprecedented periods of warming waters [START_REF] Mckinstry | Seasonal variation of zooplankton abundance and community structure in Prince William Sound, Alaska, 2009-2016[END_REF][START_REF] Evans | Significant shifts in coastal zooplankton populations through the 2015/16 Tasman Sea marine heatwave[END_REF]) is likely to exacerbate the long-term bottom-up effect on higher-trophic levels [START_REF] Möllmann | Effects of climate and overfishing on zooplankton dynamics and ecosystem structure: regime shifts, trophic cascade, and feedback loops in a simple ecosystem[END_REF], Sandford et al. 2019[START_REF] Osborne | Breeding seabirds increase foraging area in response to an extreme marine heatwave[END_REF]. This may particularly intensify over the coming decades as such events are predicted to increase in magnitude and frequency [START_REF] Oliver | Projected marine heatwaves in the 21st century and the potential for ecological impact[END_REF]). In addition, considering the various anthropogenic perturbations in marine ecosystems (e.g. overfishing and pollution) and the rapidly changing oceanographic conditions, seabird flexibility may be increasingly challenged by the predicted intensification of extreme events such as marine heatwaves [START_REF] Grémillet | Spatial ecology and conservation of seabirds facing global climate change: a review[END_REF], Oliver et al. 2019).

Due to their high wing-loading [START_REF] Warham | Wing loading, wing shapes, and flight capabilities of Procellariiformes[END_REF], the limited capacity of small diving seabird species to extend their foraging range during years of poor prey availability may impede their ability to adapt to more extreme environmental variations (Elliott et al. 2013).

Additionally, unlike all other procellariiform species, the absence of stomach oil for diving petrels compels adults to deliver meals to their chick at high frequency [START_REF] Roby | Chick feeding in the diving petrels Pelecanoides georgicus and P. urinatrix exsul[END_REF], Eizenberg et al. 2021). With more intense marine heatwaves predicted [START_REF] Oliver | Projected marine heatwaves in the 21st century and the potential for ecological impact[END_REF]), these constraints may affect diving petrel capacity to adapt to more frequent extreme events, and ultimately impact colony recruitment and drive local population/species declines [START_REF] Bost | Large-scale climatic anomalies affect marine predator foraging behaviour and demography[END_REF][START_REF] Péron | Projected poleward shift of king penguins' (Aptenodytes patagonicus) foraging range at the Crozet Islands, southern Indian Ocean[END_REF]. Indeed, the small population size of Peruvian [START_REF] Cristofari | Unexpected population fragmentation in an endangered seabird: the case of the Peruvian divingpetrel[END_REF] and Whenua Hou (Pelecanoides whenuahouensis; [START_REF] Fischer | Analyses of phenotypic differentiations among South Georgian diving petrel (Pelecanoides georgicus) populations reveal an undescribed and highly endangered species from New Zealand[END_REF]) diving petrels, or the geographic isolation of common diving petrels in Bass Strait (Fromant et al. 2020b) may exacerbate the long-term effects of climate change.

In conclusion, the present study highlighted the sensitivity of a small macrozooplanktonic avian feeder, the common diving petrel, to environmental variability.

While the time-series of the present study was relatively short, marine heatwave events were found to have a major impact at a regional scale on the food webs on which rely diving petrels.

This suggests that common diving petrels in Bass Strait may have reached a critical threshold above which buffering the effects of such intense events on their reproductive output is not possible. In addition, the long-term effects of marine heatwaves on marine predators remain undescribed, and understanding their impact on adult survival is a key point for long-lived species. Focusing on species such as diving petrels, with high foraging constraints and feeding on low trophic-level prey, could help to disentangle the underlying mechanisms of long-term adaptation to climate change. Considering the wide geographic distribution (longitudinal and latitudinal gradients) of the common diving petrel throughout different environments of the Southern Hemisphere, this abundant seabird could act as a suitable environmental sentinel to monitor the effects of changing oceanographic conditions.

(Figure 1 :

 1 Figure 1: Left panel: Number of days per year with mean sea surface temperature above 19°C in Bass Strait, south-eastern Australia. Each dot corresponds to one year, and dots with a specified year correspond to the periods when blood samples were collected from common diving petrels on Kanowna Island (2008-2010 in Fromant et al. 2020c; 2017-2020 in the present study). The 19 °C threshold was selected based on the optimal temperature range of coastal krill (12-18 °C; Sheard 1953). A linear model was fitted to the data (red line; the analyses of residual and autocorrelation function plots showed no temporal autocorrelation pattern). Right panel: Whole blood δ 13 C and δ 15 N values of common diving petrels (P. urinatrix) from Kanowna Island during cold (blue 40% ellipse and 100% total convex hull; 2009, 2017 and 2020) and warm years (red 40% ellipse and 100% total convex hull; 2008, 2010, 2018 and 2019). Incubation, dot symbols: red = 2018; black = 2019; light blue = 2020. Chick-rearing, square symbols: green = 2017; yellow = 2018; dark blue = 2020. Grey dots were adapted from Fromant et al. (2020c) (light grey, incubation 2008; dark gray, incubation 2009; open grey, incubation 2010).

  distance travelled per trip nor the proportion of time foraging, with no relation found between the daylight duration (a proxy of available foraging time) and both the total distance travelled (Spearman's correlation test: S = 1024604, P = 0.221, rho = 0.089) and the proportion of time spent foraging (Spearman's correlation test: S = 1202794, P = 0.239, rho = -0.086).

Figure 2 :

 2 Figure 2: Upper panels: Foraging kernel density distribution estimated from GPS locations of common diving petrels (P. urinatrix) in incubation (upper left) and chickrearing (upper right) from Kanowna Island, south-eastern Australia. Solid and open kernel areas show the 50 and 95% of the kernel utilization distribution, respectively (core area and home range, respectively). Lower panels: Distribution density for maximum distance from colony to foraging locations per foraging trip of common diving petrel in incubation (lower left) and chickrearing (lower right) periods.

  74.5% in 2018, 46.2% in 2019 and 66.7% in 2020. During the chick-rearing period, the proportion ranged between 100.0% in 2017 and 2020, and 80.0% in 2018. The longest trips (3 days) were observed during the incubation periods 2018 and 2019. Similarly, the proportion of time at sea spent in foraging/resting state varied inter-annually and between incubation and the chick-rearing periods (Kruskal-Wallis test: χ 2 = 69.74, df = 3, P < 0.001); it was negatively correlated with the total distance travelled, for both 1 d trips (Fig.3; Spearman's correlation test: S = 1254374, P < 0.001, rho = -0.840) and 2 d trips (Spearman's correlation test: S = 2890, P = 0.002, rho = -0.632).

Figure 3 :

 3 Figure 3: Correlation between the proportion of time spent foraging and total distance travelled per 1-day trip of common diving petrels (P. urinatrix) in incubation (left panels) and during the chick-rearing periods (right panels). The vertical and upper panels give the distribution density of the proportion of time spent foraging per trip and the total distance travelled per trip, respectively. The size of each point is proportional to the trip duration (< 24h). Trips longer than 24h with overnight period at sea were not included in this figure.

  SEAB overlap = 48%). During the same breeding season, both δ 13 C and δ 15 N values were significantly higher in incubation than during the chick-rearing period. Values of δ 13 C were minimum in chick-rearing 2017 and maximum in incubation 2018 (ranging from ̶ 22.2 to ̶ 18.4 ‰), while δ 15 N values were minimum in incubation 2019 and maximum in incubation 2020 (ranging from 11.6 to 15.4 ‰). The isotopic niche width was larger in incubation 2018 and 2019 (Fig. 4; Table

Figure 4 :

 4 Figure 4: Whole blood δ 13 C and δ 15 N values of common diving petrels (P. urinatrix) from Kanowna Island in incubation (INC: red, 2018, n =23; black, 2019, n = 20; light blue, 2020, n = 9) and chick-rearing (CR: green, 2017, n = 51; yellow, 2018, n = 16; dark blue, 2020, n = 15). Incubation 2008-2010 (grey) are whole blood δ 13 C and δ 15 N values of common diving petrels in incubation from Kanowna Island obtained fromFromant et al., 2020Fromant et al., (2008, n = 10;, n = 10; 2009, n = 4; 2010, n = 15). Full lines correspond to the 40% ellipse and dashed lines 100% total convex hull. The blue and red writing represent cold and warm years, respectively (see Figure1).

Figure 5 :

 5 Figure 5: Cause-effect diagram illustrating the bottom-up effect of marine heatwaves on the breeding output of zooplankton-eating seabirds.For species breeding on the edge of their distribution range, the predicted intensification of marine heatwaves is likely to strengthen the detrimental effects on their breeding output. Full red blocks and arrows are results observed in the present study; Dotted red blocks and arrows are adapted from the literature[START_REF] Young | Seasonal and interannual variability in krill (Nyctiphanes australis) stocks and their relationship to the fishery for jack mackerel (Trachurus declivis) off eastern Tasmania, Australia[END_REF], Harding et al. 2007[START_REF] Cohen | Changes in prey availability impact the foraging behaviour and fitness of Cape gannets over decade[END_REF][START_REF] Oliver | The unprecedented 2015/16 Tasman Sea marine heatwave[END_REF][START_REF] Evans | Significant shifts in coastal zooplankton populations through the 2015/16 Tasman Sea marine heatwave[END_REF]) (photo ©: A. Slotwinski and G. Jones)

Figure S1 :

 S1 Figure S1: Fitted functions for each environmental covariate used to assess the probability of habitat selection of common diving petrels (P. urinatrix) from Kanowna Island, south-eastern Australia.Environmental covariates include (in increasing order of importance): salinity (SAL), wave direction (WVD), sea surface temperate (SST), sea surface height (SSH), current speed (CUR), wave period (WVP), sea floor slope (SLO), bathymetry (DEP) and mixed layer thickness (MLT).

Figure S2 :

 S2 Figure S2: Fitted functions for each year and breeding stage of habitat selection of common diving petrels (P. urinatrix) from Kanowna Island, south-eastern Australia. Environmental covariates: salinity (SAL), sea surface height (SSH), sea surface temperate (SST), wave period (WVP), current speed (CUR), wave direction (WVD), sea floor slope (SLO), bathymetry (DEP) and mixed layer thickness (MLT).

Figure S2:

  Figure S2:

Table 1 : Model performance (AUC) and relative importance of environmental variables for the habitat selection models for common diving petrels (P. urinatrix) from Kanowna (Bass Strait, south-eastern Australia).

 1 Breeding success varied substantially between the four years of the study (Pearson's Chi-squared test, χ 2 = 127.73, P < 0.001), from 69% in 2017 (n = 16) and 84% in 2020 (n = 50), to 6% in 2018 (n = 66) and 0% in 2019 (n = 63) (Table2). The very low breeding success in 2018 and 2019 was related to a delayed breeding season (a 30-50 days delay compared to the breeding seasons of 2017 and 2020; Kruskal-Wallis test: χ 2 = 112.75, P < 0.001), and related to low egg and chick survival (Table2;Pearson's Chi-squared test, χ 2 = 46.291, P < 0.001 and χ 2 = 90.391, P < 0.001, respectively). The low hatching and breeding success in warmer years were associated with longer trips in 2018 (no data in 2019), larger foraging areas (in both 2018 and 2019) and lower whole blood δ 15 N values (in both 2018 and 2019) (see Sections 3.3. and 3.4.).

		Model	AUC Salinity	Sea surface temperate	Sea surface height	Wave period	Wave direction	Current speed	Sea floor slope	Bathymetry	Mixed layer thickness
	Combined years and breeding stages	0.96	18.4%	11.4%	11.2%	10.8%	12.3%	11.2%	10.3%	8.0%	6.5%
	2017 Chick-rearing 0.96	41.5%	9.4%	8.2%	8.5%	8.4%	5.6%	7.2%	8.8%	2.5%
	2018	Incubation Chick-rearing 0.96 0.96	28.5% 7.1%	5.6% 9.3%	8.5% 12.1%	12.8% 12.2%	13.6% 17.8%	13.7% 15.3%	5.1% 10.9%	7.0% 14.2%	5.1% 1.2%
	2019	Incubation	0.97	14.1%	20.3%	16.5%	12.6%	10.4%	6.4%	5.4%	5.1%	9.1%
	2020	Incubation Chick-rearing 0.94 0.97	11.6% 23.8%	9.7% 15.6%	7.6% 8.0%	11.5% 5.7%	19.4% 13.6%	5.4% 15%	12.6% 9.4%	7.5% 8.6%	14.6% 0.4%

Table 2 : Hatching, fledging and breeding success of common diving petrel (P. urinatrix) from Kanowna Island (Bass Strait, south-eastern Australia).

 2 For each parameter, values not sharing the same superscript letter (a, b or c) are significantly different (P < 0.05; Pearson's chi-squared test).

	Year	Hatching success	Fledging success	Breeding success
	2017	81% (n = 16) a	90% (n = 32) a	69% (n = 16) a
	2018	36% (n = 66) b	17% (n = 24) b	6% (n = 66) b
	2019	41% (n = 63) b	0% (n = 26) c	0% (n = 63) c
	2020	92% (n = 50) a	91% (n = 46) a	84% (n = 50) a

Table 3 : Summary of foraging trip metrics (mean ± SE) for GPS-equipped common diving petrels (P. urinatrix) on Kanowna Island, Bass Strait, south-eastern Australia.

 3 In 2017, no bird was tracked during incubation due to logistical constraints. In 2019, no bird was tracked during the chick-rearing period because of the early breeding failure of all the study individuals. For each parameter, values not sharing the same superscript letter (a, b or c) are significantly different (P < 0.05; Mann-Whitney U test for distance and time related parameters, and Rao's spacing test for bearings).

Table 4 : Summary of δ 13 C and δ 15 N values in whole blood of common diving petrels (P. urinatrix) from Kanowna Island (Bass Strait, south-eastern Australia) during the incubation and chick-rearing periods.

 4 Values are means ± SD, with the number of individuals given in brackets. Values not sharing the same superscript letter (a, b, c, d or e) are significantly different (P < 0.05; multiple comparisons with Tukey method for p-value adjustment).

Table S2 : Results of the GLMM models explaining trip parameters for common diving petrels from Kanowna Island in incubation (2018, N = 18; 2019, N = 12; 2020, N = 6) and during the chick-rearing period (2017, N = 38; 2018, N = 12; 2020, N = 15).

 S2 Explanatory variables, Akaike Information Criterion (AIC), Delta AIC (difference in AIC with the best model) and Log-likelihood are given for each model. Models are ranked according to their respective AIC value.

	Model	AIC	Delta AIC Log-likelihood
	Total trip duration ~ YEAR * BREEDING STAGE	1261.7	0	-622.9
	Total trip duration ~ YEAR	1264.0	5.2	-626.0
	Total trip duration ~ BREEDING STAGE	1295.0	36.1	-643.5
	Total trip duration ~ SEX	1310.2	51.4	-651.1
	Total trip duration ~ 1	1312.0	53.1	-652.9
	Total distance per trip ~ YEAR * BREEDING STAGE	1991.0	0	-987.5
	Total distance per trip ~ YEAR	2010.4	22.2	-999.2
	Total distance per trip ~ BREEDING STAGE	2057.7	69.5	-1024.8
	Total distance per trip ~ SEX	2063.7	75.3	-1027.8
	Total distance per trip ~ 1	2069.6	81.3	-1031.8
	Maximum distance per trip ~ YEAR * BREEDING STAGE	1677.7	0	-830.8
	Maximum distance per trip ~ YEAR	1691.3	16.3	-839.7
	Maximum distance per trip ~ BREEDING STAGE	1732.9	57.9	-862.5
	Maximum distance per trip ~ SEX	1739.7	64.7	-865.9
	Maximum distance per trip ~ 1	1744.1	68.9	-869.0
	Start direction ~ YEAR * BREEDING STAGE	1682.7	0	-833.3
	Start direction ~ YEAR	1738.6	60.2	-863.3
	Start direction ~ BREEDING STAGE	1768.6	90.1	-880.3
	Start direction ~ SEX	1769.9	91.5	-880.9
	Start direction ~ 1	1774.2	95.8	-884.1
	Maximum range direction ~ YEAR * BREEDING STAGE	1665.3	0	-824.7
	Maximum range direction ~ YEAR	1722.4	66.6	-855.2
	Maximum range direction ~ BREEDING STAGE	1756.4	100.9	-874.2
	Maximum range direction ~ SEX	1758.4	102.5	-875.2
	Maximum range direction ~ 1	1762.7	106.8	-878.3

Table S3 : Total area of the convex hull (TA), Bayesian standard ellipses areas (SEAB) and SEAB overlap of isotopic values in whole blood of common diving petrels (P. urinatrix) from Kanowna Island, south-eastern Australia

 S3 . INC = incubation; CR = Chick-rearing.

		CR 2017	INC 2018	CR 2018	INC 2019 INC 2020	CR 2020
	TA	1.23	3.47	0.34	4.61	0.28	0.21
	SEAB	0.30	1.08	0.16	2.22	0.19	0.11
	Overlap -CR 2017	-	0.00	0.06	0.05	0.00	0.03
	Overlap -INC 2018	-	-	0.02	0.48	0.05	0.03
	Overlap -CR 2018	-	-	-	0.05	0.00	0.02
	Overlap -INC 2019	-	-	-	-	0.09	0.05
	Overlap -INC 2020	-	-	-	-	-	0.15
	Overlap -CR 2020	-	-	-	-	-	-

Acknowledgements

Fieldwork was conducted on Wamoon country, land of the Boon Wurrung, Bunurong and Gunaikurnai people. The authors thank the numerous volunteers for their help in the field, and G. Guillou from the Plateforme Analyses Isotopiques of the LIENSs laboratory for running stable isotope analysis. Thanks to the CPER (Contrat de Projet Etat-Région) and the FEDER (Fonds Européen de Développement Régional) for funding the IRMS of LIENSs laboratory.

The IUF (Institut Universitaire de France) is acknowledged for its support to P. Bustamante as a Senior Member. We also thank two anonymous reviewers for their constructive comments on the manuscript.

Funding statement

This study was supported logistically and financially by Sea World Research and Rescue Foundation Inc. and Birdlife Australia.

Author Contributions

AF conceived the study, collected field data, did the statistical analyses and drafted the manuscript; KD and JAB participated in the data analysis, helped drafting the manuscript and critically revised it; YHE, AL, JAB, BRG participated to the data collection, helped drafting the manuscript and critically revised it; MBF, PB and YC were involved in stable isotopes analysis, helped drafting the manuscript and critically revised it; JPYA, CAB participated in the conception and coordination of the study, helped drafting the manuscript and critically revised it.

Competing Interests

The authors declare there are no competing interests

Supplementary materials

Impact of extreme environmental conditions: foraging behaviour and trophic ecology responses of a diving seabird, the common diving petrel.

Supplementary text: Estimating the potential effects of short-term deployments of miniaturised devices on adult common diving petrels.

In October/November 2017, adult birds were equipped during the chick-rearing period with lightweight GPS (n = 38; nanoFix-GEO, Pathtrack Ltd, Otley, United-Kingdom) attached to two tail feathers using waterproof tape. The total mass of the equipment (GPS) corresponded to 2.3 ± 0.2% of the birds' body mass (1.8 -2.7%, n = 38). The devices were deployed for 1 to 4 consecutive days (2.2 ± 0.8 days), and all the GPS were recovered. Individuals were weighed (± 2 g; Pesola) before and after the deployment and retrieval of the device, respectively.

All the individuals remained in their burrow after handling until departure time the next morning. Birds equipped with a GPS departed on average 1.47 ± 0.05 hours before sunrise and return 1.67 ± 0.02 hours after sunset. This is in accordance with field observation and passive acoustic studies showing that common diving petrels leave the colony on average 1-2 hours before sunrise and return to the colony 1-2 hours after sunset [START_REF] Thoresen | Observations on the breeding behaviour of the diving petrel Pelecanoides u. urinatrix (Gmelin)[END_REF][START_REF] Ranjard | MatlabHTK: a simple interface for bioacoustics analyses using hidden Markov models[END_REF]Fromant et al. unpublished data).

All untracked birds and individuals equipped with a GPS did daily trips. There was no significant variation in body mass of instrumented individuals between the deployment and the retrieval (130 ± 2 g and 134 ± 2 g, respectively; n = 38; Mann-Whitney U test: U = 1085, P = 0.151). Similarly, there was no difference between the body mass of birds when retrieved and control individuals (134 ± 2 g and 133 ± 1 g, respectively; n = 38 and 89, respectively; Mann-Whitney U test: U = 2191.5, P = 0.737). These results are consistent with [START_REF] Navarro | Diving capabilities of diving petrels[END_REF] that found no effect of TDRs deployment on trip duration and body mass of common and South Georgian diving petrels in South Georgia.

Growth curve analysis method [START_REF] Mirman | Growth Curve Analysis and Visualization Using R[END_REF] was used to investigate the potential effect of GPS deployment of parent birds on chick growth. Chicks were monitored approximately every 3-5 d, depending on weather conditions. Individuals were weighed in a cloth bag with a Pesola spring scale (± 2 g), bill and tarsus measurements were taken with Vernier callipers (± 0.1 mm) and wing length was measured with a shoulder stopped ruler (± 1.0 mm). The growths of body mass, wing length, tarsus length and bill length were modelled with a third-order orthogonal polynomial and fixed effects on all age terms of conditions (Control = no deployment versus Instrumented = adults equipped with a GPS). The model also included chick-ID random effects and chick-ID by condition random effects. For all studied parameters (body mass, wing length, tarsus length and bill length), there was no significant effect of device deployment on the intercept term nor the curvature (Table S1), which indicates similar growth rates between the two groups.

Similarly, fledging success and fledging body mass of chicks did not differ between control and experimental groups (91% and 95% fledging success; 128 ± 3 g and 126 ± 2 g for control and experimental groups, respectively; paired t-test: t11.755 = 0.622, P = 0.546).