Nicolas Deguines
email: nicodeguines@gmail.com

Romain Lorrilliere
email: lorrilliere@mnhn.fr

Anne Dozières
email: anne.dozieres@mnhn.fr

Carmen Bessa-Gomes
email: carmen.bessa-gomes@universite-paris-saclay.fr

François Chiron
email: francois.chiron@universite-paris-saclay.fr

Any despot at my table? Competition among native and introduced bird species at garden birdfeeders in winter

Keywords: Citizen Scientists, France, Interference competition, Pica pica, Psittacula krameri, Serious game, Streptopelia decaocto

Garden bird feeding constitutes a massive provision of food that can support bird communities, but there is a growing concern it might favour the establishment of exotic species that could be detrimental to others. How bird species compete with novel species for this anthropogenic food resources needs to be assessed.

Here, we investigated competition in wintering bird communities at garden birdfeeders. We evaluated whetherand how muchbird access to resources is hampered by the presence of putative superior competing species, among which the Rose-ringed parakeet, the most abundant introduced species across Europe.

Using the nation-wide citizen science scheme BirdLab, in which volunteers record in real-time bird attendance on a pair of birdfeeders during 5-minute sessions, we tested whether i) cumulative bird presence time and richness at birdfeeders, and ii) species probability of presence at birdfeeders, were influenced by three large species (the Eurasian magpie, the Eurasian collared-dove, and the Rose-ringed parakeet). Additionally, we assessed whether the Rose-ringed parakeet occupied resources significantly more than others.

Presence of the Rose-ringed parakeet or the Eurasian collared-dove similarly reduced community cumulative presence time at birdfeeders, but only the dove reduced community richness. Each of the three large species influenced the presence of at least one of the six smaller species that could be separately modelled, but effects varied in strength and direction.

The Rose-ringed parakeet and the Eurasian collared-dove were among the three species monopolising birdfeeders the longest, substantially more than the Eurasian magpie.

Our findings confirm the competitive abilities of the large species studied, but do not suggest that garden bird feeding may alarmingly favour introduced species with detrimental effects on native species. Given the variability of large species' effects on small passerines,

INTRODUCTION

Evidence that anthropogenic resource subsidies to wildlife can have major effects on ecosystems functioning traces back eight centuries ago [START_REF] Douglas | Prehistoric Inuit whalers affected Arctic freshwater ecosystems[END_REF], and this probably occurred to some extent since millennia [START_REF] Oro | Ecological and evolutionary implications of food subsidies from humans[END_REF]. Resources associated to human activities and made available to wildlife, voluntarily or not, can improve the physiological conditions of individuals able to consume these subsidies [START_REF] Yom-Tov | Body sizes of carnivores commensal with humans have increased over the past 50 years[END_REF], increase breeding success (Robb et al., 2008b) and lead to population increases [START_REF] Galbraith | Supplementary feeding restructures urban bird communities[END_REF][START_REF] Oro | Ecological and evolutionary implications of food subsidies from humans[END_REF][START_REF] Plummer | The composition of British bird communities is associated with long-term garden bird feeding[END_REF]. In turn, in both aquatic and terrestrial realms, food web dynamics can be affected following modification in ecosystem production [START_REF] Singer | Anthropogenic subsidies alter stream consumer-resource stoichiometry, biodiversity, and food chains[END_REF] or species interactions [START_REF] Arcos | Competition between the yellow-legged gull Larus cachinnans and Audouin's gull Larus audouinii associated with commercial fishing vessels: The influence of season and fishing fleet[END_REF][START_REF] Cortés-Avizanda | Resource unpredictability promotes species diversity and coexistence in an avian scavenger guild: a field experiment[END_REF][START_REF] Newsome | The ecological effects of providing resource subsidies to predators[END_REF][START_REF] Osterback | Longterm shifts in anthropogenic subsidies to gulls and implications for an imperiled fish[END_REF][START_REF] Rodewald | Anthropogenic resource subsidies decouple predator-prey relationships[END_REF]. In recent decades, garden bird feeding strongly increased, involving millions of households worldwide and constituting a theoretical supply of food for millions of birds (Robb et al., 2008a). How this release of a key limiting factor of bird populations [START_REF] Newton | Population limitation in birds[END_REF][START_REF] Siriwardena | The effect of supplementary winter seed food on breeding populations of farmland birds: evidence from two large-scale experiments[END_REF], especially during winter, affect bird communities has yet to be fully comprehended.

From a conservation perspective, garden bird feeding may have pros and cons. In urban areas, where bird diversity has been reduced [START_REF] Chace | Urban effects on native avifauna: A review[END_REF][START_REF] Marzluff | Worldwide urbanization and its effects on birds[END_REF] and population declines may be particularly worrying [START_REF] Cbs | Decline in 13 out of 20 urban bird populations[END_REF]SDES and AFB, 2018;[START_REF] Sullivan | Using habitat-specific population trends to evaluate the consistency of the effect of species traits on bird population change[END_REF], garden bird feeding is generally considered beneficial. In species using feeders, with no change for others, thus resulting in more diverse communities.

However, potential detrimental effects are known: nutritionally unbalanced food items can reduce egg production [START_REF] Plummer | Fat provisioning in winter impairs egg production during the following spring: a landscapescale study of blue tits[END_REF], birds' enhanced proximity may increase probability of disease transmission [START_REF] Galbraith | Experimental feeding regime influences urban bird disease dynamics[END_REF][START_REF] Lawson | Health hazards to wild birds and risk factors associated with anthropogenic food provisioning[END_REF], and predation risks could be elevated [START_REF] Tryjanowski | Who started first? Bird species visiting novel birdfeeders[END_REF]. A major additional concern is the possibility that this provision of readily available food resources could favour the establishment of exotic species. For example, experimental work from the North Island of New Zealand showed that supplementary feeding restructured bird communities to the benefit of exotic species, that were mostly granivorous [START_REF] Galbraith | Supplementary feeding restructures urban bird communities[END_REF]. In Europe, the introduced Rose-ringed parakeet (Psittacula krameri) thrives in cities and has become the most abundant exotic bird species [START_REF] Pârâu | Rose-ringed parakeet populations and numbers in Europe: a complete overview[END_REF]. Garden bird feeding may provide a staple enhancing its survival and its colonisation in temperate climates [START_REF] Clergeau | Bird feeders may sustain feral Rose-ringed parakeets Psittacula krameri in temperate Europe[END_REF].

So far, the Rose-ringed parakeet literature focused on competition for nesting sites [see [START_REF] White | Assessing the ecological and societal impacts of alien parrots in Europe using a transparent and inclusive evidence-mapping scheme[END_REF] for a review], whereas this species commonly use birdfeeders [START_REF] Clergeau | Bird feeders may sustain feral Rose-ringed parakeets Psittacula krameri in temperate Europe[END_REF] where it may display the most agonistic behaviours [START_REF] Le Louarn | Interference competition between an invasive parakeet and native bird species at feeding sites[END_REF]. Body mass is another important factor determining species' abilities to compete for supplementary feeding at birdfeeders [START_REF] Francis | Effects of supplementary feeding on interspecific dominance hierarchies in garden birds[END_REF]. To our knowledge, only one study compared potential effects of the Rose-ringed parakeet to a similarly large and dominant native species (the Great spotted woodpecker) at the community-level: presence of a caged bird of either of the latter two species reduced bird visits and feeding, but the Rose-ringed parakeet's effects were stronger [START_REF] Peck | Experimental evidence of impacts of an invasive parakeet on foraging behavior of native birds[END_REF]. However, Peck & colleagues' (2014) work was a year-round experiment, and competition outcomes could markedly differ in wintering bird communities exposed to a variety of abiotic and biotic stresses, i.e. under cold conditions and depleted resources [START_REF] Pravosudov | Energy management in passerine birds during the nonbreeding season[END_REF]Robb et al., 2008b), and when birdfeeders may represent a critical source of food in urban areas. Additionally, there is a need to investigate these questions while controlling for the influence that other large species could have, and with data of bird interactions between free-living individuals.

Our study aims to investigate competition in wintering bird communities at garden birdfeeders, and to evaluate whether an introduced species hampers access to resources. We use data from the Citizen Science scheme BirdLab [START_REF] Lorrilliere | Winter bird survey in French gardens, two complementary schemes for a wide array of questions[END_REF] to carry out a large-scale assessment encompassing different French populations of the Rose-ringed parakeet and various environmental contexts (e.g. urban landscapes, climates), strengthening the representativity of our analysis [START_REF] Devictor | Beyond scarcity: citizen science programmes as useful tools for conservation biogeography[END_REF]. Coupling a serious game and observations of free-living bird individuals, BirdLab engages volunteers in collecting bird cooccurrences at birdfeeders following a standardised protocol. As bird species differ in their use of birdfeeders and their ability to cope with novelty [START_REF] Tryjanowski | Urbanization affects neophilia and risk-taking at bird-feeders[END_REF][START_REF] Tryjanowski | Who started first? Bird species visiting novel birdfeeders[END_REF], we assess responses at both community-and species-level, expecting species may fare differently in competing for resources. Most importantly, we evaluate whether effects of the Rose-ringed parakeet vary from those of two similarly large and potentially aggressive species: the Eurasian magpie (Pica pica) and the Eurasian collared-dove (Streptopelia decaocto). In Winter, seeds -and potentially other plant materials -constitute the diet of these three large species [START_REF] Clergeau | Bird feeders may sustain feral Rose-ringed parakeets Psittacula krameri in temperate Europe[END_REF][START_REF] Poling | Dietary overlap and foraging competition between Mourning doves and Eurasian collared-doves[END_REF][START_REF] Reebs | Regurgitated pellets and late winter diet of Black-billed magpies, Pica pica, in Central Alberta[END_REF][START_REF] Shiels | Diets of Kauai's invasive rose-ringed parakeet (Psittacula krameri): evidence of seed predation and dispersal in a human-altered landscape[END_REF][START_REF] Tatner | The diet of urban Magpies Pica Pica[END_REF]. While the collared-dove does not spur as much debate as the Rose-ringed parakeet, both arrived in Europe recently (in particular in France, in the early 1950s and 1970s respectively), in contrast with the Eurasian magpie present in Europe by the Middle Pleistocene [START_REF] Jánossy | Die mittelpleistozäne fauna der höhle des hungária-berges bei Dorog (Gerecse Gebirge, Ungarn)[END_REF]. Specifically, we tested whether community cumulative presence time and richness at birdfeeders varied between four treatments: control (absence of any large species) and presence of either the Eurasian magpie, the Eurasian collared-dove, or the Rose-ringed parakeet. To better understand these community-level patterns, we then estimated the time the Rose-ringed parakeet occupied exclusively (i.e., as the only species present) birdfeeders and tested whether it differs from other species' exclusive occupation of birdfeeders. Finally, we investigated whether the presence of either the Eurasian magpie, the Eurasian collared-dove, or the Rose-ringed parakeet influenced the probability of presence of six small species at birdfeeders. Following previous research (Le Louarn et al., 2016;[START_REF] Peck | Experimental evidence of impacts of an invasive parakeet on foraging behavior of native birds[END_REF], we hypothesised the Rose-ringed parakeet may hamper birds' access to feeders more than the other two large birds, the Eurasian magpie and the Eurasian collared-dove.

MATERIALS AND METHODS

DATA COLLECTION

BirdLab (the Feederwatch citizen science project database for France) is a citizen science program in which volunteers follow a standardised protocol to record birds visiting birdfeeders during winter [START_REF] Lorrilliere | Winter bird survey in French gardens, two complementary schemes for a wide array of questions[END_REF]. To participate, volunteers set up a pair of identical birdfeeders (hereafter referred to as a 'station'), distant from 1-2 m from each other.

Stations can be private (e.g., in private gardens) or shared (e.g., at a university campus or in a public garden). Each birdfeeder is provided with sunflower seeds, the most preferred food supplement in various human-dominated landscapes [START_REF] Tryjanowski | Food preferences by birds using bird-feeders in winter: a large-scale experiment[END_REF]. Volunteers participate by using a user-friendly application (developed for tablet and smartphone on Android or iOS) in which the two birdfeeders are represented: during a five-minute session, icons of bird species are dragged and dropped to feeders, mimicking movements of the freeliving bird individuals visiting the station (Fig. 1). Volunteers thus record in real-time bird arrivals (Fig. 1b), shifts between birdfeeders (Fig. 1c) and departures (Fig. 1d). Each fiveminutes session starts when the volunteer drags in the first bird icon on a feeder. The application includes 27 species commonly seen at birdfeeders in France [START_REF] Lorrilliere | Winter bird survey in French gardens, two complementary schemes for a wide array of questions[END_REF]. All 27 species are easily recognized. Nonetheless, the BirdLab application uses timed quizzes to test both bird recognition (made intuitive by relying on icons instead of names) and the speed of dragging-dropping bird icons. Passing the first quiz is mandatory to participate at the 'beginner' level (i.e., 14 bird species are available); succeeding in subsequent quizzes (i.e., being able to recognize among more species timely) allows reaching three next levels: 'Amateur' (17 species), 'Confirmed' (26 species) and 'Expert' (27 species). Participation in BirdLab is possible in winter (from November 15 th to March 31 st ) since 2014.

For each session, the geographical coordinates of the station are obtained using the GPS of the volunteer's device (tablet or smartphone), along with the date and time of the observation. From each BirdLab session, for each bird, we obtain its species, and when exactly it was present on which birdfeeder. Individuals are not marked and we thus cannot know the actual number of unique individuals per species that were present during a session.

For the purpose of the present study, the information we retrieved was, for a given species and session, when exactly it was present and how many simultaneous individuals there were at a station, i.e. combining birdfeeders and allowing to compute a cumulative presence time per species and per session.

DATA SELECTION

We applied several filters relative to data quality and data specificity needed for the biological questions asked in the present paper.

A few sessions included an unlikely high number of species present simultaneously at the station (e.g., reaching 23 out of 27 species), and this most probably indicated that the protocol had not been followed. We determined which stations produced any of the top 1% of sessions in terms of the number of species simultaneously present at birdfeeders, and removed all sessions from these stations. Remaining sessions had from 0 to 7 species present simultaneously, which is in agreement with our experience of the BirdLab protocol. We removed stations where more than ten volunteer accounts recorded sessions, in order to reduce the variability due to multiple volunteers using a station. Additionally, we kept data from experienced volunteers only by excluding i) the first and second sessions recorded at each station, and ii) sessions recorded at the 'beginner' level (see 2.3 for the inclusion of this variable in our statistical models). Sessions carried out in an insufficient level of daylight were removed: we kept those from 30 mn before sunrise to 30 mn after sunset [given the location and date of the sessions, and using the sunrise function of the maptools package [START_REF] Bivand | maptools: Tools for handling spatial objects[END_REF] of R version 3.5.2. (R Core Team, 2018)]. Finally, when two sessions from a station had been recorded less than 30 minutes apart, we randomly kept only one to avoid potential temporal auto-correlation between samplings.

As the Rose-ringed parakeet was added to the BirdLab application on 15 th November 2017, our dataset spans winters 2017/2018 and 2018/2019. We kept sessions recorded in December, January or February, excluding November and March for which the limited number of sessions precluded their inclusion as levels of the categorical variable 'month' in our models. We selected sessions from stations where the Rose-ringed parakeet had been recorded at least once, and further included stations present within 10 km. While maintaining the landscape context (i.e., dominated by urban land-use; Fig. 2b) and the bird communities (i.e., common species found in urban gardens) similar across stations, this allowed us to obtain a dataset fitting our scientific objective: assessing how the presence of large species (European magpie, Eurasian collared-dove, and Rose-ringed parakeet) may affect bird communities at birdfeeders compared to when all large species were absent. To do so, we selected sessions in which none or only one of the three large species studied had been recorded. Importantly, the sessions kept never included other large species present in the Journal Pre-proof J o u r n a l P r e -p r o o f corone, the Rock dove Columba livia, the Common woodpigeon Columba palumbus, and the Great spotted woodpecker Dendrocopos major), for which the lack of sufficient data prevented their inclusion in the present study. Most volunteers installed birdfeeders of the platform type, and data from stations with birdfeeders of the hanging type were too scarce to be included in the present analysis.

In the end, the total dataset included 818 sessions from 33 stations (Fig. 2), totalling over 68 hours of observations. Among the 27 species considered in the BirdLab program, 21 were included in our final dataset (Table 1).

STATISTICAL ANALYSES

We relied on mixed-effects modelling to investigate how the three large species could affect winter bird communities at the stations included in our dataset. All statistical analyses were performed using R version 3.5.2 (R Core Team, 2018) and mixed-effects models were performed with the lme4 package [START_REF] Bates | Fitting linear mixed-effects models using lme4[END_REF]. Below, we first describe the two models investigating bird responses at the community-level (cumulative presence time and richness).

Second, we present the model estimating how long each species is the only species present per session. Finally, we describe seven models testing for large species effect on the presence/absence of small species.

2.3.1.Community-level

For each session, we computed cumulative presence time and richness of the community (i.e., the 18 small species in Table 1). We used these as the response variables of two separate linear mixed-effects models. To obtain the cumulative presence time, we summed the time for each individual of a species if multiple individuals were present.

Journal Pre-proof J o u r n a l P r e -p r o o f 10 Cumulative presence time was log-transformed to meet the assumption of normality of model residuals (see below). Sessions recorded at the same station are not independent of each other, and we thus included 'Station_ID' as a random intercept effect in both models.

The same set of explanatory variables were included in the two models. A large species treatment variable was included (categorical with four levels: 'Absence', 'European magpie present', 'Eurasian collared-dove present', 'Rose-ringed parakeet present'), with 'Absence' of large species being the reference level (i.e., the models tested whether the presence of either of the three large species differed from when all were absent). Other explanatory variables were: winter (categorical variable with two levels: '2017/2018', '2018/2019'), month (categorical variable with three levels: 'December', 'January', 'February'), volunteer expertise (categorical variable with three levels: 'Amateur', 'Confirmed', 'Expert') and the longitude and latitude of stations (continuous variables) to account for potential spatial auto-correlation in our dataset. We computed variance inflation factors [START_REF] Zuur | Mixed effects models and extensions in ecology with R, Statistics for Biology and Health[END_REF] of explanatory variables and found no evidence of collinearity (all VIF values < 2).

We graphically checked that the residuals of each model met the assumptions of homoscedasticity and normality [START_REF] Faraway | Extending the linear model with R : generalized linear, mixed effects and nonparametric regression models[END_REF][START_REF] Zuur | Mixed effects models and extensions in ecology with R, Statistics for Biology and Health[END_REF]. For each model, we graphically confirmed the spatial independence of the residuals by computing a spline correlogram [START_REF] Zuur | Mixed effects models and extensions in ecology with R, Statistics for Biology and Health[END_REF] using the ncf R package [START_REF] Bjornstad | ncf: spatial covariance functions[END_REF]. Both models had a sample size of 818 (i.e., number of sessions).

Species exclusive occupancy of a station

To better understand how large species may affect others, we ran a linear mixed-effect model estimating how much time per session each species occupied a station as the only species present, and testing whether it differed from the time the Rose-ringed parakeet occupied a station as the only species present. The recorded times of exclusive occupancy of a station per session were not independent of each other: there were multiple times measured per session (one for each species present), and multiple sessions were recorded per station.

We modelled this structuration in the data by including 'Session_ID' nested within 'Station_ID' as a random intercept effect in the model.

The response variable was the species cumulative presence time occupying a station as the only species present per session. A session begins when a bird icon is dragged on a feeder, and the first step for the volunteer is to add the birds that may already be present at either of the two birdfeeders. To account for this design of the protocol that could slightly bias the time a species occupies a station as the only species present, we excluded initial and short sequences of time (i.e., less than 5 seconds within the first 30 seconds) that a species was recorded at the station as the only species present in a session. The resulting cumulative time occupying a station as the only species present per species and session was log-transformed (after adding 1 to each value, to cope with 0'soccurring for a species present in a session but never occupying a station as the only species present) to meet the assumption of normality of model residuals.

In this model, we included 'Species' as an explanatory variable (categorical with 17 levels, corresponding to the 17 species which occurred in at least 20 sessions; Table 1), with 'Rose-ringed parakeet' being the reference level (i.e., the model tested whether the cumulative time occupying a station as the only species present per session of a given species differed from the Rose-ringed parakeet value). An additional explanatory variable was the cumulative time of all other species present during the given session, as this could influence the time that a given species occupied the station as the only species present during the session. Other explanatory variables were winter, month, volunteer expertise, and the longitude and latitude of stations. Variance inflation factors [START_REF] Zuur | Mixed effects models and extensions in ecology with R, Statistics for Biology and Health[END_REF] of explanatory variables indicated no worrisome collinearity (all VIF values < 2).

We graphically confirmed that model residuals met the assumptions of homoscedasticity, normality and spatial independence [START_REF] Faraway | Extending the linear model with R : generalized linear, mixed effects and nonparametric regression models[END_REF][START_REF] Zuur | Mixed effects models and extensions in ecology with R, Statistics for Biology and Health[END_REF]. The sample size was 2780 (i.e., number of times species were present in the 818 sessions). We controlled the risk of type I error due to multiple testing in this model (in particular with the 17 levels of the explanatory variable Species) by correcting P values using the false discovery rate control [START_REF] Verhoeven | Implementing false discovery rate control: increasing your power[END_REF].

Small species probability of presence

We performed separate generalised linear mixed-effects models to test whether the presence of small species differed between sessions with no large species or with one of either the three large species present. Six species had sufficient records in our dataset to be modelled separately (listed as 'Commonly recorded small species' in Table 1), and we pooled the remaining 12 species to model them as a group (listed as 'Other small species' in Table 1).

To account for the lack of independence between sessions recorded at the same station, we included 'Station_ID' as a random intercept effect in the seven models.

In each model, the response variable was binary, corresponding to a species (or the group of other species) being present (1) or absent (0) in a session, and it was therefore modelled with a binomial family and a logit link function.

The same set of explanatory variables were included in the seven models. Again, the large species treatment variable was included, with 'Absence' of large species being the reference level. Additionally, we added as an explanatory variable the cumulative presence time of all other species present (except the large one, if present) during the given session, as this could influence the probability of a species to be present in a session. Finally, each model also included as explanatory variables winter, month, volunteer expertise, and the longitude and latitude of stations. Computing variance inflation factors [START_REF] Zuur | Mixed effects models and extensions in ecology with R, Statistics for Biology and Health[END_REF] of explanatory variables, we found no evidence of collinearity (all VIF values < 2).

Each model used a subset of the total dataset, tailored to modeling the presence and absence of each species (or the group of 12 species). For each model, we determined in each winter the dates of first and last records of the modelled species and restrained the dataset to sessions within these dates. Then, we only kept sessions from stations where the modelled species had been recorded at least once. In the resulting dataset, we followed [START_REF] Austin | Events per variable (EPV) and the relative performance of different strategies for estimating the out-of-sample validity of logistic regression models[END_REF] and checked that there were at least 20 sessions per continuous variable and level of categorical variables. This requirement was met for the six species modelled separately, although one level of a categorical variable had to be dropped in the House sparrow model (effect of the Rose-ringed parakeet presence could not be tested). We had to group the 12 remaining species to verify this condition, unmet when kept separated. The final sample sizes for these seven models are provided in Figure 5. In each model, we checked there was no over/under-dispersion and no zero-inflation using the R package DHARMa [START_REF] Hartig | DHARMa: Residual diagnostics for hierarchical (multi-Level / mixed) regression models[END_REF]; we also followed [START_REF] Faraway | Extending the linear model with R : generalized linear, mixed effects and nonparametric regression models[END_REF] and graphically checked model residuals using the R package arm [START_REF] Gelman | arm: data analysis using regression and multilevel/hierarchical models[END_REF]. The assumption of spatial independence of model residuals was graphically confirmed.

RESULTS

In presenting the results of our models, statistically significant relationships were considered for p-values lower than 0.05.

COMMUNITY-LEVEL

The cumulative presence time of small species was significantly lower in the presence of either the Eurasian collared-dove (94.4 s, i.e. -33%) or the Rose-ringed parakeet (80.5 s, i.e. -43%) in comparison with sessions free of large species (Fig. 3a, Table 2). Presence of the Eurasian magpie was not significantly associated with a change in the cumulative presence time of small species. On average, volunteers of the highest level of expertise ('Expert') recorded significantly longer cumulative presence time of small species per session than 'Amateur' volunteers (Table 2).

Compared to sessions without large species, we only detected a significant difference in small species richness in the presence of the Eurasian collared-dove (Fig. 3b, Table 2), which was associated to 0.46 fewer species in average (i.e. -13%). In contrast, the presence of the Eurasian magpie or the Rose-ringed parakeet were not significantly associated with changes in the richness of small species in a session. On average per session, both 'Confirmed' and 'Expert' volunteers recorded significantly higher small species richness than 'Amateur' volunteers (Table 2).

SPECIES EXCLUSIVE OCCUPANCY OF A STATION

Over the 41 sessions in which the Rose-ringed parakeet was recorded, it occupied a station as the only species present during 26.3 s per session on average (Fig. 4). Out of the 16 other species for which such an estimation could be computed, only the European goldfinch and the Eurasian collared-dove tended to occupy a station as the only species present for a longer period of time, although the difference with the Rose-ringed parakeet was not significant (Table 3). The Eurasian magpie (with 5.5 s) was among the 11 species that occupied stations as the only species present for a significantly shorter duration than the Roseringed parakeet. No significant effect of volunteer expertise was detected (Table 3).

SMALL SPECIES PROBABILITY OF PRESENCE

Among the six small species whose probability of presence could be modelled separately, the presence of four species was significantly associated with the presence of at least one large species (Fig. 5, Table 4). Presence of the Rose-ringed parakeet was significantly associated with a substantial reduction in the probability of presence of the European robin. Presence of the Eurasian magpie and the Eurasian collared-dove were associated with significantly reduced probability of presence of the Eurasian blue tit, and the Eurasian collared-dove was also associated with a decreased probability of presence of the Great tit. Interestingly, there were some positive associations between the presence of a large species and the probability of presence of some small species, although this pattern was only significant between the Eurasian collared-dove and the House sparrow (Fig. 5, Table 4).

As a group, the probability of presence of the 12 small species that could not be modelled separately was not significantly associated with the presence of any of the three large species.

Compared to sessions from 'Amateur' volunteers, sessions from 'Confirmed' volunteers were more likely to include the European robin and sessions from 'Expert' volunteers were more likely to include the Great tit (Table 4). Additionally, the probability of presence of the group of 12 small species ('Other small species') was significantly higher in sessions from both 'Confirmed' and 'Expert' volunteers.

DISCUSSION

Within urban environments where garden bird feeding in winter represents a novel and increasing anthropogenic food supplement, we examined the competition within bird communities and evaluated the competitive roles of large and/or novel species. Using data from a nation-wide and innovative citizen science scheme recording bird attendance and cooccurrences at birdfeeders, we found that the introduced Rose-ringed parakeet was among the most preemptive competitor species (i.e., occupying a pair of birdfeeders exclusively) and that this led to reduced community-level presence time at birdfeeders. However, delving into cooccurrences of species, the probability of presence of only one species (the European robin) out of six was significantly reduced in the presence of the Rose-ringed parakeet. Most importantly, we compared the effects of the Rose-ringed parakeet with two other large species and our findings suggest that while the competition for food resources differ from the other two large species at the species-level, it does not have a larger effect at the community-level.

Our findings, with complementary work on the Rose-ringed parakeet's competition for nesting sites [START_REF] Strubbe | Assessing the potential impact of invasive ring-necked parakeets Psittacula krameri on native nuthatches Sitta europeae in Belgium[END_REF], are in agreement with a theoretical and empirical body of knowledge suggesting that competition from introduced to native species is not expected to have large effects [START_REF] Davis | Biotic globalization: does competition from introduced species threaten biodiversity?[END_REF], in birds in particular [START_REF] Martin-Albarracin | Impact of nonnative birds on native ecosystems: a global analysis[END_REF].

We are aware of only two studies that assessed competition for food resources from the Rose-ringed parakeet, and the analysis of our large dataset (68.2 hours of observations) of free-living birds at birdfeeders complement and expand our previous understanding of the Rose-ringed parakeet's potential effect. Our results at the community-level empirically confirm the experimental work of [START_REF] Peck | Experimental evidence of impacts of an invasive parakeet on foraging behavior of native birds[END_REF] who had found that a caged Rose-ringed parakeet or its calls reduced feeding rate. From four hours of video recordings of birds at birdfeeders, Le Louarn et al. ( 2016) suggested that the Rose-ringed parakeet displayed the most antagonistic behaviours among eight species, including the Eurasian collared-dove. However, we found that the two species similarly reduced community cumulative presence time and that only the dove was associated with lower community richness. This discrepancy highlights that predicting community-level responses from behaviours between individual pairs is not straightforward. Indeed, out of six small species, we found that three displayed a probability of presence at birdfeeders negatively associated with one or more large species, and that one species (the House sparrow) was positively associated to one of the large species (Fig. 5). These various patterns of co-occurrences at feeding sites may result from direct and indirect effects of competitive interactions within bird communities [START_REF] Wootton | The nature and consequences of indirect effects in ecological communities[END_REF], that may buffer detrimental effects of antagonistic encounters. Further examination of cooccurrences among and between small and large species at birdfeeders will be critical to untangle the net ecological effects of any species in the community.

In common with previous work studying bird competition in urban areas (Le Louarn et al., 2016;[START_REF] Peck | Experimental evidence of impacts of an invasive parakeet on foraging behavior of native birds[END_REF][START_REF] Tryjanowski | Food preferences by birds using bird-feeders in winter: a large-scale experiment[END_REF], the extent with which relying on birdfeeders as food resources may represent competition for natural resources is uncertain.

Food resources for wintering birds are arguably less spatially aggregated in natural or agricultural settings compared to seeds on birdfeeders, and preemptive competition for wild resources may thus be less important than we observed with feeders. However, given the prominence of garden bird feeding in urban areas (Robb et al., 2008a) and how these anthropogenic food subsidies affect the temporal dynamics of bird communities [START_REF] Plummer | The composition of British bird communities is associated with long-term garden bird feeding[END_REF], competition at birdfeeders may represent a substantial part of competition for food resources in urban landscapes, especially in winter. Additionally, the BirdLab protocol is to use sunflower seeds, but birds have dietary preferences [START_REF] Francis | Effects of supplementary feeding on interspecific dominance hierarchies in garden birds[END_REF][START_REF] Poling | Dietary overlap and foraging competition between Mourning doves and Eurasian collared-doves[END_REF][START_REF] Tryjanowski | Food preferences by birds using bird-feeders in winter: a large-scale experiment[END_REF] that can influence investment in foraging and/or competition. In the future, the BirdLab protocol could thus open up to different food items for volunteers to use at birdfeeders, in order to investigate how resource identity affects competition within bird communities. This perspective could also provide insights into why, out of the three large species, only the Eurasian magpie stayed short periods on birdfeeders (Table 1), whereas all three large species rely on seeds and other plant materials during winter [START_REF] Clergeau | Bird feeders may sustain feral Rose-ringed parakeets Psittacula krameri in temperate Europe[END_REF][START_REF] Poling | Dietary overlap and foraging competition between Mourning doves and Eurasian collared-doves[END_REF][START_REF] Tatner | The diet of urban Magpies Pica Pica[END_REF].

Considerable research efforts are devoted to understanding how exotic species may affect native species [START_REF] Godet | What conservation does[END_REF][START_REF] Simberloff | Impacts of biological invasions: what's what and the way forward[END_REF]. However, evaluating the effects of introduced species may be difficult when lacking a comparison with functionally equivalent native species. In this paper, we included not only a native equivalent (the Eurasian magpie) of the Rose-ringed parakeet but also a neonative species [the Eurasian collared-dove, which naturally colonised the country; following the definition of Essl and colleagues (2019)]. Because the neonative species has now widely spread in France since its colonisation about two decades before the introduced Rose-ringed parakeet, the native bird communities could be more habituated to its competitive pressure than that of the Rose-ringed parakeet. However, interestingly, our results at both community-and species-level suggest the neonative species to be a greater competitor for these anthropogenic food subsidies than the Rose-ringed parakeet. Additionally, the large native and exotic species did not affect the same species at birdfeeders. Therefore, to better understand, predict and manage the effects that any species -regardless its origin -may have on ecosystems, we emphasise that ecologists should focus on species traits [START_REF] Davis | Don't judge species on their origins[END_REF][START_REF] Fournier | Predicting future invaders and future invasions[END_REF], for example, body mass, trophic and nesting preferences, or phenology [START_REF] Orchan | The complex interaction network among multiple invasive bird species in a cavity-nesting community[END_REF].

Relying on citizen science -"the involvement of volunteers in scientific research" [START_REF] Dickinson | Citizen science as an ecological research tool: challenges and benefits[END_REF] was essential to this study. Citizen science has proven highly valuable to advance research in a wide range of disciplines [START_REF] Cooper | The invisible prevalence of citizen science in global research: migratory birds and climate change[END_REF][START_REF] Mckinley | Citizen science can improve conservation science, natural resource management, and environmental protection[END_REF][START_REF] Theobald | Global change and local solutions: Tapping the unrealized potential of citizen science for biodiversity research[END_REF]. While data quality or sampling bias may raise analytical challenges, appropriate project design (e.g. standardised protocol, methods to engage volunteers), post-collection filtering and/or validation of data, and statistical solutions can overcome most existing limitations [START_REF] Bird | Statistical solutions for error and bias in global citizen science datasets[END_REF][START_REF] Follett | An analysis of citizen science based research: usage and publication patterns[END_REF][START_REF] Serret | Data quality and participant engagement in citizen science: comparing two approaches for monitoring pollinators in France and South Korea[END_REF]. We here acknowledge that a limitation of the BirdLab dataset is the impossibility to validate observations a posteriori and to rule out identification errors. However, we argue that our results can be trusted for three reasons. First, we only kept data from experienced volunteers and further adjusted for volunteers' expertise in all statistical models. Second, the BirdLab protocol is limited to 27 very common and easily recognizable species, and this is particularly true of the three large species (especially the Rose-ringed parakeet) and the six small passerines which were analyzed separately (Fig. 5). Last but not least, identification errors from any volunteers should be largely independent of the variable of interest in the present analysis, i.e. presence or absence of a large species, and therefore have very little qualitative impact on our findings. The fact that we detected significant effects of volunteer' expertise in several of our models highlights that accounting for volunteer experience when analysing citizen science data may be essential to ensure that effects of ecological variables of interest are as unbiased as possible.

Within only two years, the BirdLab scheme gathered a sufficiently large dataset of standardised observations to assess competition from the Rose-ringed parakeet, still a spatially restricted species in France despite being the most abundant exotic bird in Europe [START_REF] Pârâu | Rose-ringed parakeet populations and numbers in Europe: a complete overview[END_REF]. Effects from the two novel species (Rose-ringed parakeet and Eurasian collared-dove) on the attendance at birdfeeders would be better estimated if we had data prior arrivals. These data are lacking so far; however, with expanding Rose-ringed parakeet populations in France [START_REF] Clergeau | Dynamique de population de la perruche à collier Psittacula krameri introduite en Île-de-France[END_REF], the BirdLab scheme will be in a unique position to determine how an exotic bird integrate and potentially modify community interactions in winter. Documenting such community interactions changes at birdfeeders may be critical to understanding the mechanisms behind temporal species abundance trends revealed by longterm monitoring, emphasizing the interest of coupling complementary citizen science scheme [START_REF] Lorrilliere | Winter bird survey in French gardens, two complementary schemes for a wide array of questions[END_REF]. For example, this could help disentangle effects and causes of concomitant native and exotic populations temporal trends [START_REF] Colléony | When the winners are the losers: invasive alien bird species outcompete the native winners in the biotic homogenization process[END_REF]. This illustrates how valuable citizen science can be to advance our knowledge of biological Journal Pre-proof J o u r n a l P r e -p r o o f 20 invasions [START_REF] Roy | Increasing understanding of alien species through citizen science (Alien-CSI)[END_REF], beyond other ecological goals and educational benefits [START_REF] Deguines | Assessing the emergence of probiodiversity practices in citizen scientists of a backyard butterfly survey[END_REF][START_REF] Deguines | Fostering close encounters of the entomological kind[END_REF][START_REF] Mckinley | Citizen science can improve conservation science, natural resource management, and environmental protection[END_REF].

CONCLUSIONS

Garden bird feeding is an increasingly popular activity that provides food supplement to birds and can restructure entire communities [START_REF] Galbraith | Supplementary feeding restructures urban bird communities[END_REF][START_REF] Plummer | The composition of British bird communities is associated with long-term garden bird feeding[END_REF].

In this study, we sought to examine how wintering birds compete for this novel resource and cope with a large and putatively competitive exotic species. We directly compared the introduced Rose-ringed parakeet with two similarly large and potentially aggressive (neo)native species and, thanks to an innovative semi-experimental citizen science scheme, investigated this issue with national-scale data of free-living birds attending birdfeeders. At the community-level, we found that the Rose-ringed parakeet and the Eurasian collared-dove reduced community cumulative presence time at birdfeeders. However, only the dove also reduced community richness. This is in line with our findings that the Rose-ringed parakeet and the Eurasian collared-dove were the strongest preemptive competitor (i.e., monopolising birdfeeders), in contrast with the Eurasian magpie. Interestingly, at the species-level, responses to the three large species varied in strength and direction (positive or negative associations), calling for further considerations of interspecific direct and indirect interactions.

For example, antagonistic encounters among large species, native or introduced, could have ripple effects on smaller passerines and key ecosystem functions (e.g. seed dispersion, insect predation). This, and the opportunity in future years to monitor how the most abundant exotic bird in Europe integrate local communities, constitute critical fundamental and applied research perspectives which the BirdLab citizen science program should be able to tackle thanks to the involvement of volunteers.

Table 1. List of the 21 species included in the study. 'Large species', 'Commonly recorded small species' (species which response to large species presence could be separately estimated, see Methods and Fig. 5) and 'Other small species' (species that were pooled before estimating an overall response to large species presence, see Methods and Fig. 5) are ordered by decreasing number of sessions they were recorded in. The mean body mass was retrieved from Demongin and colleagues (2020). 2) from the 'Absent' treatment. Bars are 95% confidence intervals estimated from the models, using R package ciTools [START_REF] Haman | ciTools: confidence or prediction intervals, quantiles, and probabilities for statistical models[END_REF]. 3). Bars are 95% confidence intervals estimated from the model, using R package ciTools [START_REF] Haman | ciTools: confidence or prediction intervals, quantiles, and probabilities for statistical models[END_REF]. respectively; Table 4). The six separate small species are ordered from left to right by the median time of presence during a session (Table 1), and sample sizes (n) are provided below each species name. Bars are 95% confidence intervals estimated from the models, using R package ciTools [START_REF] Haman | ciTools: confidence or prediction intervals, quantiles, and probabilities for statistical models[END_REF]. Effect of the Rose-ringed parakeet on the House sparrow could not be estimated (see 2.3.3).

Figure 1 .

 1 Figure 1. BirdLab protocol. Panel (a) shows how the station is represented in the BirdLab

Figure 2 .

 2 Figure 2. Localisation of the 33 BirdLab stations. In (a), crosses correspond to the stations.

Figure 3 .

 3 Figure 3. Community-wide changes in the presence of large species. Average community

Figure 4 .

 4 Figure 4. Species exclusive occupancy of a station per session. Squares are estimates (from

Figure 5 .

 5 Figure 5. Associations between small species and large species presence. Probability of

ACKNOWLEDGEMENTS

We warmly thank all volunteers of the BirdLab scheme. We are grateful to the NGO LPO and to the Vigie-Nature team for help in managing BirdLab. We thank the editor and two anonymous reviewers for providing helpful and constructive comments. ND and RL were funded by the BiodivERsA3-2015-104 (BIOVEINS) grant. The funding source had no involvement in study design or execution.

AUTHORS' CONTRIBUTIONS

ND, RL, FC and CBG conceptualized the ideas and designed the methodology; ND analysed the data, designed the figures, and led the writing of the manuscript; RL curated the data; AD, RL, FC and CBG managed the BirdLab scheme. All authors contributed critically to the drafts and gave final approval for publication.

Table 2. Results of the community-level mixed effects models. Predictors' estimates are shown for the linear mixed-effects models (Cumulative presence time, Richness), along with their associated standard errors (SE), and P-values (P). 'EM', 'ECD' and 'RRP' respectively stand for the 'European magpie', the 'Eurasian collared-dove', and the 'Rose-ringed parakeet'. When P<0.05, statistics are shown in bold.

Declaration of competing interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Graphical abstract

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HIGHLIGHTS

-Citizen scientists record birds at birdfeeders through a serious game -Community effects of Rose-ringed parakeet were compared with two similar species -Bird community use of feeding resources was hampered by two of three large species -Each large species differently affected other species' use of birdfeeders -Garden bird feeding may not greatly favor introduced over native bird species