# How does habitat use influence PFAS contamination in wildlife? Combining stable isotopes and GPS tracking in three gull species

David Rozen-Rechels, Prescillia Lemesle, William Jouanneau, Manrico

Sebastiano, Stephanie M Harris, Pierre Blévin, Frédéric Angelier, Julien

Gernigon, Jean-Christophe Lemesle, Frédéric Robin, et al.

► To cite this version:

David Rozen-Rechels, Prescillia Lemesle, William Jouanneau, Manrico Sebastiano, Stephanie M Harris, et al. How does habitat use influence PFAS contamination in wildlife? Combining stable isotopes and GPS tracking in three gull species. Environmental Pollution, 2025, 10.1016/j.envpol.2025.127556. hal-05428655

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How does habitat use influence PFAS contamination in wildlife? Combining stable isotopes and GPS tracking in three gull species

David Rozen-Rechels, Prescillia Lemesle, William Jouanneau, Manrico Sebastiano, Stephanie M. Harris, Pierre Blévin, Frédéric Angelier, Julien Gernigon, Jean-Christophe Lemesle, Frédéric Robin, Hélène Budzinski, Pierre Labadie, Paco Bustamante, Olivier Chastel

PII: S0269-7491(25)01930-X

DOI: https://doi.org/10.1016/j.envpol.2025.127556

Reference: ENPO 127556

To appear in: *Environmental Pollution*

Received Date: 6 October 2025

Revised Date: 28 November 2025

Accepted Date: 16 December 2025

Please cite this article as: Rozen-Rechels, D., Lemesle, P., Jouanneau, W., Sebastiano, M., Harris, S.M., Blévin, P., Angelier, F., Gernigon, J., Lemesle, J.-C., Robin, F., Budzinski, H., Labadie, P., Bustamante, P., Chastel, O., How does habitat use influence PFAS contamination in wildlife? Combining stable isotopes and GPS tracking in three gull species, *Environmental Pollution*, https://doi.org/10.1016/j.envpol.2025.127556.

This is a PDF of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability. This version will undergo additional copyediting, typesetting and review before it is published in its final form. As such, this version is no longer the Accepted Manuscript, but it is not yet the definitive Version of Record; we are providing this early version to give early visibility of the article. Please note that Elsevier's sharing policy for the Published Journal Article applies to this version, see: https://www.elsevier.com/about/policies-and-standards/sharing#4-published-journal-article. Please also note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2025 Published by Elsevier Ltd.

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3 gull species

11 PFAS

<figure><img src="image_4.png" /></figure>

Foraging ecology

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /></figure>

GPS-TRACKING

European herring gull

<figure><img src="image_7.png" /></figure>

Terrestrial - Coastal

RELATIONS PFAS &
HABITAT USE

High trophic &
marine resources
= ↑ PFCAs

Lesser black-backed gull

<figure><img src="image_8.png" /></figure>

Terrestrial - Coastal - Offshore

RELATIONS PFAS &
HABITAT USE

compound specific

Great black-backed gull

<figure><img src="image_9.png" /></figure>

Coastal

<figure><img src="image_10.png" /></figure>

NO RELATION PFAS &
HABITAT USE

<figure><img src="image_11.png" /></figure>
1 How does habitat use influence PFAS contamination in wildlife?

2 Combining stable isotopes and GPS tracking in three gull species

3

4 David Rozen-Rechels¹,²*¥, Prescillia Lemesle²,³*¥, William Jouanneau², Manrico Sebastiano⁴, Steph-

5 anie M. Harris⁵,⁶, Pierre Blévin⁷, Frédéric Angelier², Julien Gernigon⁸, Jean-Christophe Lemesle⁸,

6 Frédéric Robin⁸, Hélène Budzinski⁹, Pierre Labadie⁹, Paco Bustamante³, Olivier Chastel²

7

8 ¹Sorbonne Université, Université Paris Cité, Univ Paris Est Créteil, CNRS, IRD, INRAE, Institut

9 d'écologie et des sciences de l'environnement de Paris, IEES Paris, F-75005 Paris, France

10 ²Centre d'Etudes Biologiques de Chizé (CEBC), UMR 7372 CNRS - La Rochelle Université, 79360

11 Villiers-en-Bois, France

12 ³Littoral Environnement et Sociétés (LIENSs), UMR 7266 CNRS - La Rochelle Université, 17000

13 La Rochelle, France

14 ⁴Behavioural Ecology & Ecophysiology Group, Department of Biology, University of Antwerp, 2610

15 Wilrijk, Belgium

16 ⁵School of Environmental Sciences, University of Liverpool, Liverpool, L59 3GP, United Kingdom

17 ⁶School of Ocean Sciences, College of Environmental Science and Engineering, Bangor University,

18 Menai Bridge, LL59 5AB, United Kingdom

19 ⁷Akvaplan-niva AS, Fram Centre, P.O. Box 6606 Langnes, 9296 Tromsø, Norway

20 ⁸Ligue pour la Protection des Oiseaux (LPO), 17300 Rochefort, France

21 ⁹Bordeaux University, EPOC, UMR 5805 CNRS, 33405 Talence, France

22

23 ¥ co-first authors
24 **Corresponding authors:** David Rozen-Rechels, david.rozen-rechels@sorbonne-universite.fr and

25 Prescillia Lemesle, prescillia.lemesle@cebc.cnrs.fr

26 **Keywords:** contaminant; biologging; trophic ecology, movement ecology; seabird; Atlantic

27

28
29 **GRAPHICAL ABSTRACT**

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3 gull species

<figure><img src="image_13.png" /></figure>

11 PFAS

<figure><img src="image_14.png" /></figure>

**Foraging ecology**

<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /></figure>

GPS-TRACKING

European herring gull

<figure><img src="image_17.png" /></figure>

Terrestrial - Coastal

<figure><img src="image_18.png" /></figure>

RELATIONS PFAS &
HABITAT USE

High trophic &
marine resources

= ↑ PFCAs

Lesser black-backed gull

<figure><img src="image_19.png" /></figure>

Terrestrial - Coastal - Offshore

<figure><img src="image_20.png" /></figure>

RELATIONS PFAS &
HABITAT USE

compound specific

Great black-backed gull

<figure><img src="image_21.png" /></figure>

Coastal

<figure><img src="image_22.png" /></figure>

NO RELATION PFAS &
HABITAT USE

30

31 Highlights:

32 • The influence of habitat uses on PFAS contamination was studied in three gull species.

33 • PFAS levels were combined with GPS tracking and stable isotopes (δ¹³C; δ³⁴S, δ¹⁵N).

34 • Association between PFAS concentrations and foraging ecology was species-dependent.

35 • Coastal foraging habitat could be a source of PFAS contamination.
36 **ABSTRACT**

37 Per- and polyfluoroalkyl substances (PFAS) are toxic and persistent compounds widely distributed
38 in the environment and accumulate in top predators, including seabirds. Because of the biomagnifi-
39 cation potentials of some PFAS, diet is thought to be a key exposure route for PFAS. However, other
40 factors, such as habitat use, may mask interspecific differences in PFAS exposure expected from
41 trophic structure. Among seabirds, gulls are generalist that forage in both terrestrial and marine hab-
42 itats, making them relevant models to concurrently investigate the influence of foraging habitats and
43 trophic position on PFAS exposure. We combined plasma PFAS concentrations with GPS tracking
44 and stable isotopes to define foraging habitats (δ¹³C; δ³⁴S; GPS) and trophic positions (δ¹⁵N) in three
45 sympatric gull species breeding in France (Isle of Ré). In herring gulls (*Larus argentatus*), long-chain
46 perfluoroalkyl carboxylic (PFCAs) were positively correlated with high trophic resources from ma-
47 rine habitats. We found compound- and sex-dependent relationships between PFAS concentrations
48 and stable isotope values in lesser black-backed gulls (*Larus fuscus*), while no association was found
49 with habitat use. No association was found between PFAS levels and stable isotopes in great black-
50 backed gulls (*Larus marinus*). Our study suggests that coastal habitat could be a source of PFCA
51 contamination and highlights that the influence of habitat use on gull exposure to PFAS varied de-
52 pending on species, sex, and compounds.
53

53
54 **INTRODUCTION**

55 Per- and poly-fluoroalkyl substances (hereafter PFAS) include thousands of synthetic organic 56 compounds (Schymanski et al., 2023) which are widely used in many manufacturing products (e.g., 57 cosmetics, food packaging, non-stick cookware, waterproof textiles, medical devices, pesticides, and 58 firefighting foams) (Gaines, 2023). With a stable chemical structure formed by fluorine atoms at- 59 tached to a carbon chain (Buck et al., 2011), PFAS have unique chemical and physical properties that 60 make them extremely persistent in the environment (“Forever chemicals”). PFAS are now ubiquitous 61 and commonly found in humans and wildlife tissues worldwide (De Silva et al., 2021; Sinclair et al., 62 2020). This led to growing concerns about the consequences of PFAS exposure for human health and 63 the environment (DeWitt, 2015; Fenton et al., 2021). Indeed, PFAS are reported to be carcinogenetic, 64 immunotoxic, neurotoxic, and to act as endocrine-disruptors (Fenton et al., 2021; Ma et al., 2023, 65 2022). Consequently, three PFAS and their salts (perfluorooctanesulfonic acid -PFOS-, perfluorooc- 66 tanoic acid -PFOA- and perfluorohexanesulphonic acid -PFHxS-) have been listed under the Stock- 67 holm Convention on Persistent Organic Pollutants (United Nations, 2020).

68 In wildlife, seabirds are commonly used as bioindicators of environmental pollution (Elliott 69 and Elliott, 2013), because they accumulate significant levels of PFAS with detrimental effects on 70 their physiology and fitness (Ask et al., 2021; Blévin et al., 2017a, 2017b; Costantini et al., 2022; 71 Humann-Guilleminot et al., 2024; Melnes et al., 2017; Sebastiano et al., 2023, 2020; Tartu et al., 72 2014). Due to the biomagnification potentials of some PFAS (Conder et al., 2008; Lewis et al., 2022), 73 concentrations are significantly higher in seabirds situated at the top of marine food webs suggesting 74 that diet represents a key exposure route for PFAS (Alfaro Garcia et al., 2022; Borgå et al., 2004; 75 Chételat et al., 2020; Roscales et al., 2019). To assess the trophic ecology of seabirds, stable isotope 76 analyses are commonly used with high carbon and sulphur values (δ¹³C and δ³⁴S, respectively) as 77 indicator of more marine feeding habitats and diet, and higher nitrogen values (δ¹⁵N) as indicator of 78 higher trophic position (Forero and Hobson, 2003; Hobson et al., 1994). Some studies have reported
positive associations between δ¹³C or δ¹⁵N values and PFAS concentrations in diverse matrices (e.g., eggs, feathers, liver, muscle, or plasma) (Gebbink et al., 2011; Padilha et al., 2022; Robuck et al., 2020). However, other studies reported conversely negative or no correlations between stable isotope values and PFAS concentrations (Bustnes et al., 2013; Carravieri et al., 2020; Gebbink et al., 2011; Hebert et al., 2022; Leat et al., 2013; Padilha et al., 2024; Robuck et al., 2020), suggesting that other factors, such as spatial movements, and habitat use may however mask interspecies differences in PFAS expected from trophic structure alone (Roscales et al., 2019). For instance, it has been suggested that the different marine environments (coastal or offshore) can influence PFAS exposure (Gebbink et al., 2011; Miller et al., 2015).

Biologging (e.g., using GPS, satellite or geolocator (GLS) devices) can provide unparalleled
fine-scale information on the spatial movements of seabirds (Burger and Shaffer, 2008). The use of
such loggers in addition to stable isotope values can be of great interest for understanding the origin
of seabird contamination (Baak et al., 2024; Elliott and Elliott, 2013). However, studies linking con-
taminant loads to avian movements have mainly focused on other substances (e.g., trace elements or
polybrominated diphenyl ethers) than PFAS, which have to our knowledge received little attention
(reviewed in Baak et al., 2024). Previous work using GLS have investigated the influence of the
wintering areas on blood PFAS concentrations of black-legged Kittiwakes (Rissa tridactyla) and an-
cient murrelets (Synthliboramphus antiquus) (Léandri-Breton et al., 2024; Miller et al., 2020), and
suggests that migratory seabirds can act as biovectors of PFAS to Arctic nesting sites (Léandri-Breton
et al., 2024). Regarding GPS, a limited number of studies have used this technology to investigate the
link between PFAS contamination and fine-scale foraging movements during the breeding season
(but see Jang et al., 2022; Wilkinson et al., 2022). However, it is essential to use the fine spatial
resolution of PFAS contamination to identify habitats that are particularly exposed to PFAS and
therefore species that are potentially vulnerable to PFAS contamination.
In the present study, we investigated the associations between plasma concentration of PFAS and habitat use, with two complementary approaches: stable isotopes (δ¹³C, δ³⁴S and δ¹⁵N) and fine-scale GPS tracking. We focused on three species of gulls (European herring gulls, herring gulls, hereafter, *Larus argentatus argenteus*, great black-backed gulls, *Larus marinus*, and lesser black-backed gulls, *Larus fuscus graellsii*) breeding in sympathy in a Natural Reserve in the south-west France and showing high plasma PFAS concentrations with interspecies variations (Sebastiano et al., 2023, 2021), but for which contamination sources are not identified. These species are opportunist and generalist feeders, being scavengers, and predators, collecting marine food at the sea surface, human wastes in landfills and earthworms in fields (Camphuysen et al., 2015; Gyimesi et al., 2016; Pennycott et al., 2020; Steenweg et al., 2011). Used habitats include offshore, coastal, and terrestrial environments with inter-individual variation depending on the species (Jouanneau et al., 2022; O'Hanlon et al., 2025). Herring gulls use primarily terrestrial/coastal habitats while great black-backed gulls and lesser black-backed gulls use mainly coastal habitats or a mixture of terrestrial and offshore habitats, respectively (Jouanneau et al., 2022; O'Hanlon et al., 2025). This multi-species sampling allows to assess if foraging ecology, proxied by stable isotopes and localization of foraging sites with GPS-tracks, is an important driver of PFAS concentrations for these three species and between individuals. We hypothesized that i) high trophic resources (δ¹⁵N) from marine foraging habitats (δ¹³C and δ³⁴S, or revealed by GPS-tracks) would be associated to higher PFAS concentrations, as marine resources are often reported as a potential contamination pathway for seabirds (Cheng et al., 2025; Colomer-Vidal et al., 2022). We also expected that associations between PFAS concentrations and foraging ecology could be ii) dependent of the chemical structure of the PFAS, bioaccumulation and biomagnification potentials being related to increasing fluorinated carbon chain, especially in perfluorosulfonic acids (PFSAs, hereafter) and the head group, as PFSAs have higher potentials than perfluorocarboxylic acids (PFCAs, hereafter) for a same chain length (Conder et al., 2008; Lewis et al., 2022);
and iii) sex-specific, as we are aware of sex differences in foraging habitats, especially for lesser black-backed gulls (Camphuysen et al., 2015).

## 129 MATERIAL AND METHODS

PFAS concentrations and movement data used in the present study have been independently described in two previous publications: PFAS concentrations were described in Sebastiano et al., (2021), while isotopic and movement analyses were discussed in Jouanneau et al., (2022). In the present study, we focus on the association between PFAS concentrations and the foraging strategies of the species.

## 135 *Study site and species sampling*

Fieldwork was conducted during the breeding period in May 2016, 2017, and 2018 in the “Lilleau des Niges” Natural Reserve, Isle of Ré, France (46°13'53"N, 1°30'22"W). Lilleau des Niges is a 1.21 km² protected area located in the west part of the continental island, composed of salt marshes and mudflat managed by the Ligue de Protection des Oiseaux (LPO). The sampled site is located at ~30 to 50 km to three river mouths (the Sèvre Niortaise, the Charente, and the Seudre) where PFAS have been previously detected in mussels (Munschy et al., 2019, 2013; Serre et al., 2025). To date, no fluorochemical plant or PFAS-impacted industrial sites are known in this area (>20 km, Cordner et al., 2024; Ministry of Ecological Transition, Biodiversity, Forests, Sea, and Fisheries, 2025) and the nearest airport is located >20 km. This natural reserve hosts several breeding species including the three focal species: the herring gull, the lesser black-backed gull, and the great black-backed gull.

We sampled 108 adults from the three species (35 herring gulls, 44 lesser black-backed gulls, 29 great black-backed gulls, details on sample sizes per species, year and sex are summarized in Table S1). Three individuals were excluded from further physiological analyses because we were unable to perform morphological measurements or blood sampling (two of them were included in movement
tracking analyses, see below). Two individuals have been sampled twice in different years; we thus
randomly chose one observation in the next analyses to avoid pseudo-replication.

All sampled gulls were incubating eggs and were captured with a trap installed on the nest as
previously described (Jouanneau et al., 2022). Birds were ringed with both metal and plastic leg rings
engraved with a unique alphanumeric combination if it had not been ringed previously. After mor-
phological and body mass measurements (Sebastiano et al., 2021), we collected 2mL of blood from
the brachial vein. Upon return to the laboratory, blood was centrifuged at 8,000 rpm for 10 minutes
to separate the plasma and red blood cells. All samples were then stored at -20°C.

## Individual foraging behaviour

A subset of individuals (n = 43 in total, including the two individuals that were not blood
sampled) was also equipped with GPS-UHF loggers (Harrier Ecotone®, see Table S1 for details on
sample sizes by species, year and sex). The total mass of the logger and the attachment (harness) was
on average 13g, i.e., 2% or less of the weight of the individuals. We recorded locations of the bird
every five minutes from the day following blood sampling until either hatching or nest failure. Period
of raw data recording ranged from four days (two individuals) to 41 days (one individual) with an
average of 16 ± 8 (SD) days (Table S2). Despite the fact that tracking took place after blood sampling,
we considered the behaviours extracted from these locations to be representative of the foraging trips
that could explain blood PFAS concentrations, since these gulls have previously been shown to ex-
hibit high levels of individual foraging site fidelity (Jouanneau et al., 2022).

We identified foraging behaviour in GPS tracks by classifying each location as one of two
behavioural states (commuting vs. resting/foraging) using Hidden Markov models (Franke et al.,
2004) with the moveHMM package in R (Michelot et al., 2016). A foraging site was then defined as
the centroid of consecutive resting/foraging locations during a foraging trip. We identified whether
the site was in a marine (offshore or coastal: including salt marshes and intertidal zones) or in a
terrestrial habitat (any other) based on the CORINE Land cover dataset (CORINE Land Cover,
Feranec et al., 2016). For each individual, we calculated the proportion of the foraging sites located in a marine environment, with the hypothesis that this indicates a more marine diet, hereafter called the "marine foraging index". The complete procedure of the foraging sites identification is described in Supplementary Information 1.

## Molecular sexing, stable isotopes and PFAS

All individuals were sexed at the Centre d'Etudes Biologiques de Chizé (CEBC) using red blood cell samples by polymerase chain reaction amplification of two highly conserved genes of the sex chromosomes (Fridolfsson and Ellegren, 1999).

Stable isotope analyses were conducted at Littoral Environnement et Sociétés (LIENSs). The relative abundance of the three isotopes were measured from weighted sub-sample of red blood cells with a flow mass spectrometer (Thermo Scientific Delta V Advantage) coupled with an elemental analyzer (Thermo Scientific Flash EA for carbon and nitrogen; Thermo Scientific Flash EA IsoLink for sulphur). Isotope values were calculated following: δ¹³C, δ³⁴S and δ¹⁵N = ((Rsample/Rstandard) - 1) × 1000 with R being the ratio ¹³C/¹²C, ³⁴S/³²S or ¹⁵N/¹⁴N, respectively. Using internal laboratory standard, all analytical precisions were <0.2 ‰. Isotopic values were presented using the standard delta (δ) notations based on international standards, Vienna PeeDee Belemnite, Vienna Cañon Diablo troilite and atmospheric nitrogen (N₂) for δ¹³C, δ¹⁴S, and δ¹⁵N, respectively.

Eleven different PFAS were quantified in plasma samples as described in Sebastiano et al. (2021): three perfluoroalkylsulfonic acids – PFOS (linear and branched form: L-PFOS and Br-PFOS, respectively), PFHpS (L-PFHpS and Br-PFHpS), PFHxS –, seven PFCAs – PFOA (L-PFOA and Br-PFOA), PFDA, PFNA, PFUnDA, PFDoDA, PFTeDA, and PFTrDA–, one perfluoroalkane sulfonamide – FOSA –. Chemical names and structures are provided in Table S3. Only PFAS detected in >70% of samples were statistically analysed (i.e., all PFAS, except FOSA, PFOA (L-PFOA and Br-PFOA),
and Br-PFHpS). Detection frequencies, limit of detections and quantification are defined and pro-
vided in Sebastiano et al. (2021, Table S1).

202 **Statistical analyses**

203 All analyses were performed with R version 4.2.1 “Funny-Looking Kid” (R Core Team, 2020).
204 As in Jouanneau et al., (2022), a principal component analyses (PCA with “FactoMineR” R package,
205 Lê et al., 2008) was performed to reduce the number of explanatory variables and included the three
206 stable isotopes, highly and positively correlated to each other’s (see Figs. S1, S2 and Pearson corre-
207 lations *p* < 0.001 for all). The two first dimensions of the PCA (PC1 and PC2, hereafter) were kept
208 and explained 95% of the total variance. PC1 was influenced by all three isotope ratios: δ¹³C values
209 (factor loading: 0.93), δ¹⁵N values (0.93) and δ³⁴S values (0.89). The PC2 was only significantly in-
210 fluenced by δ³⁴S values (0.47). For both PC1 and PC2, high scores indicated high δ¹³C, δ³⁴S and δ¹⁵N
211 values. Individual scores for each PC were extracted to use them as predictors in statistical models.

212 A second PCA was used to examine correlations between PFAS. Most PFAS, whether PFSAs
213 or PFCAs were highly positively correlated with each other (except PFHxS), as revealed by the PCA
214 (Fig. S3). All PFAS were thus included as response variables in multivariate regression models to
215 explore compound-specific associations with predictors taking account for multiple dependences into
216 PFAS.

217 First, we aimed to investigate the influence of stable isotopes (using PC₁ and PC₂), species
218 and sex of all individuals (n = 105) on plasma PFAS concentrations using multivariate multiple re-
219 gression. First, for each PFAS independently, concentrations were log-transformed to approach a
220 Gaussian distribution. The initial linear model included PFAS concentrations as the response variable,
221 and PC₁, PC₂, their respective interactions with species or sex, and year as additive explanatory var-
222 iable. We checked multicollinearity of explanatory variables for each model using variance inflation
223 factors (Zuur et al., 2010). Large variance inflation factor scores (GVIF¹/(2.df) > 2 or VIF > 4) indicated
224 high multicollinearity between species and PCs variables and their interactions and precluded us from
running models combining species (see Table S4). Similarly, large variance inflation factor scores precluded us from running models combining sexes in lesser black backed gull and great back black gull models while there was no indication of multicollinearity in the herring gull model (see Table S5). The best models were backward selected based on Pillai's trace tests. Year was however not included in models in the case great black-backed gulls as sample size was too low (denominator degree of freedom in Pillai's test = 0). The importance of outliers was assessed by refitting all models without data showing a Cook's distance higher than 0.5 but the inclusion of such outliers did not qualitatively change the results of the analyses, and they were therefore kept in the rest of the manuscript.

Secondly, we analysed the relationship between the marine foraging index and log-transformed PFAS concentrations in birds for which we had both PFAS and GPS data for each species and sex (17 herring gulls: 9 females / 8 males; 18 lesser black-backed gulls: 8 / 10). Great black-backed gulls were excluded from spatial analyses due to limited sample size (n = 6, 3 females / 3 males) which would impact statistical power. PFAS concentrations were used as response variables in a multivariate regression model with the marine foraging index and its interaction with the sex and the species, as well as the year as additive explicative variables. We also identified multicollinearity of the marine foraging index with the species (Table S6) and sex (Table S7) variables precluding us from running models combining these variables. Sex separation for multicollinearity purposes with the two-interaction of the marine foraging index with sex reduced drastically the statistical power owing to our modest sample sizes; therefore, both sexes were analysed in the same model with sex as an additive effect (no multicollinearity in this case). We assessed the robustness of our results to the removal of observations in Supplementary Information 3.

For all the best models, heteroscedasticity and normality of residuals were checked and a significance level of α < 0.05 was used for model selection procedures (when removing a variable with a marginal effect, results with and without the variable are provided). The model selection results,
and the variance explained by each parameter of the best model are described in Tables S8–S11.

Predicted coefficients ($\beta$) presented in the results are shown with their standard errors.

## 252 RESULTS

### 253 Associations between foraging ecology and PFAS concentrations using stable isotopes

In herring gulls, PC₁ significantly explained inter-individual variations in blood PFAS concentrations (Table S8; *F*₁₀,₂₀ = 4.92, *p* = 0.01). Blood concentrations of PFCAs (excluding PFTEDA) were significantly and positively associated with PC₁ (all *p* < 0.05; all *β* > 0.1 excluding *β*ₚFTEDA = 0.09 ± 0.06, *t* = 1.52, *p* = 0.14; Figs. 1A and 2A), whereas no significant relationships were found between PFSAs and PC₁. With the exception of PFHxS, all PFAS concentrations were higher in males than in females (*F*₁₀,₂₀ = 5.6, *p* < 0.001; all *β* ≥ 0.37 and all *p* ≤ 0.02, excluding *β*ₚFHxS = -0.10 ± 0.05, *t* = -0.6, *p* = 0.5, Fig. 2B).

In lesser black-backed gull, PC₁ also explained the inter-individual variations in blood PFAS concentrations in both the female-only and the male-only models (females: *F*₁₀,₉ = 36.0, *p* < 0.001; males: *F*₁₀,₁₃I = 10.2, *p* < 0.001; Table S9). In females of lesser black-backed gulls, L-PFOS and PFUnDA concentrations were positively correlated with PC₁ (Fig. 1B; Fig. 2D: *β*ₗ-PFOS = 0.22 ± 0.09, *t* = 2.5, *p* = 0.02; Fig. 2A: *β*ₚFUnDA = 0.19 ± 0.07, *t* = 2.7, *p* = 0.01), whereas PFHxS and PFTEDA concentrations were negatively correlated with PC₁ (Fig. 2C: *β*ₚFHxS = -0.23 ± 0.06, *t* = -3.9, *p* = 0.001; *β*ₚFTEDA = -0.31 ± 0.07, *t* = -4.1, *p* < 0.001). All other PFAS concentrations were not correlated with PC₁ (all *p* > 0.16). For male lesser black-backed gulls, PFUnDA concentrations were positively correlated with PC₁ (Figs. 1B and 2A: PFUnDA: *β*ₚFUnDA = 0.11 ± 0.055, *t* = 2.3, *p* = 0.04), while PFHxS, L-PFHpS, PFDoDA, and PFTEDA concentrations were negatively correlated with PC₁ (Fig. 1; Fig 2B-C: all *β* ≤ -0.13 and all *p* < 0.007). Concentrations of all the other PFAS were not correlated to PC₁ (all *p* > 0.05). In great black-backed gulls, PC₁ significantly explained the inter-individual variations in concentrations of PFAS in females only (*F*₁₀,₃ = 28.8, *p* = 0.01; Table S10), while the best model for males was the null model. For females, only concentrations of L-PFHpS were significantly
and negatively correlated with PC1 ($\beta_{L-PFHpS}$ = -0.82 ± 0.33, *t* = -2.51, *p* = 0.03, Fig. 1C), while all the other PFAS were not correlated (all *p* > 0.05).

For all species and models, PC2 was never retained in the best models, indicating that PC2 did not significantly explain variation in PFAS concentrations (Tables S8–S10).

### Associations between foraging ecology and PFAS concentrations using GPS tracking

GPS tracks revealed that habitat use was species-dependent: herring gulls and lesser black-backed gulls showed a high inter-individual variability, foraging in diverse habitats from terrestrial to offshore. Both herring gulls and lesser black-backed gulls used terrestrial habitats, but herring gulls were mostly related to urban or even landfill areas, while lesser black-backed gulls mostly forage in fields. Lesser black-backed gulls also used offshore habitats, up to 100 km from the colony (Fig. 3A), likely foraging on fisheries discards while herring gulls restricted their use of marine environments to coastal habitats. Compared to the two other species, great black-backed gulls foraged almost exclusively in coastal habitats, including river mouths, with low individual variability (Fig. 3A).

In herring gulls, the marine foraging index significantly explained inter-individual variations in PFAS concentrations (Table S11 and Fig. 4; $F_{10,4}$ = 8.82, *p* = 0.03) while sex had a marginal non-significant effect ($F_{10,5}$ = 4.81, *p* = 0.07). All concentrations of PFCAs (except PFTEDA) as well as the PFSAs were positively correlated with the marine foraging index (all $\beta$ > 0.88, all *p* ≤ 0.04; Figs. 4A and 5). However, when the marginal effect of sex was removed during model selection (*p* = 0.07), the effect of the marine foraging index on PFAS concentrations was only marginal ($F_{10,5}$ = 3.25, *p* = 0.1). In this case, only PFNA, PFDA, PFDoDA, PFUnDA and PFHxS concentrations were significantly associated with marine foraging index (Fig. 4A; $\beta_{PFNA}$ = 1.00 ± 0.38, *t* = 2.63, *p* = 0.02; $\beta_{PFDA}$ = 1.45 ± 0.50, *t* = 2.91, *p* = 0.01; Fig. 5A: $\beta_{PFUnDA}$ = 1.45 ± 0.54, *t* = 2.68, *p* = 0.02; $\beta_{PFDoDA}$ = 1.30 ± 0.54, *t* = 2.42, *p* = 0.03; Fig. 5C: $\beta_{PFHxS}$ = 0.89 ± 0.34, *t* = 2.59, *p* = 0.02), and all other PFAS concentrations were unrelated to the marine foraging index.
In lesser black-backed gulls, the marine foraging index did not explain the differences in PFAS concentrations between individuals (Table S11 and Fig. 4B). The best model included only sex ($F_{10,7} = 28.98, p < 0.001$) with males having higher concentrations than females for all PFAS (all $\beta > 0.68$, all $p < 0.001$), except for PFHxS ($\beta_{PFHxS} = 0.33 \pm 0.22, t = 1.50, p = 0.15$).

## DISCUSSION

This study investigated multi-species associations between PFAS concentrations and foraging ecology using stable isotopes and GPS-tracking. Results showed species-specific associations between PFAS concentrations and foraging ecology inferred by the two approaches: stable isotopes and GPS tracking. Herring gulls showed an increase of PFCAs concentrations with increasing use of the marine environment. Regarding lesser black-backed gulls and great black-backed gulls, relationships between PFAS concentrations and foraging ecology were compound- and sex-dependent, with a few negative associations between specific compounds and stable isotope values. The different spatial distributions and habitat selection of the three gull species could explain contrasted associations between PFAS concentrations and the proxies of foraging ecology.

*Relationship between PFAS concentrations and foraging ecology*

Herring gulls had PFCAs concentrations positively associated with stable isotope values (mostly, $\delta^{15}$N and $\delta^{13}$C), suggesting that consumption on high trophic prey of marine origin leads to a higher exposure to these PFAS. Herring gulls used a mix of terrestrial and coastal foraging habitats and interestingly individuals were more contaminated as they forage in more coastal environments. Semi-aquatic and marine species are often reported to be more contaminated by PFAS (Guckert et al., 2023), potentially related to bioconcentration, bioaccumulation and biomagnification processes depending of the food webs (Conder et al., 2008; Hopkins et al., 2023; Kelly et al., 2024; Lewis et al., 2022). Specifically, coastal environment appear to present favorable conditions for the bioaccumulation and biomagnification of PFAS (Munoz et al., 2017a; Tansel, 2024), that could explain higher PFAS concentrations in gulls foraging in this environment. Trophic positions of the consumed preys
probably differ in terrestrial and marine environments, as suggest by the positive correlation between the marine foraging index and δ¹⁵N values (Fig S4.). Consequently, higher plasma PFAS concentrations in gulls could be explained by the consumption of higher trophic-level prey in the marine environment as compared to the terrestrial environment, as supported by higher PFAS concentrations when PC₁ increase. Interestingly, significant associations between blood PFAS concentrations and foraging ecology were compound specific. Bioaccumulation and biomagnification potentials of long-chain PFCAs could be one explanation of the positive associations between concentrations of these PFAS and stable isotope values. Previous studies have reported that the head functional group and carbon chain length play a significant role in PFAS biomagnification potentials, that increase for PFCAs with more than eight carbon atoms (Conder et al., 2008; Hopkins et al., 2023; Kelly et al., 2024; Lewis et al., 2022). Toxicokinetic (i.e., excretion, metabolism, organ distribution) of PFAS could also be compound-dependent and explain the differences found (Robuck et al., 2021).

For lesser black-backed gulls, the associations between blood PFAS concentrations and isotopic values were positives, negatives or non-significant. The positive associations between isotopic values and plasma concentrations of L-PFOS and PFUnDA suggest that individuals get contaminated by these compounds when they rely on marine resources, as suggested for herring gulls. Negative associations between PFHxS, L-PFHpS, PFDoDA or PFTeDA concentrations and stable isotope values suggested higher concentrations for lesser black-backed gulls relying on terrestrial habitats. In open seawaters, PFAS can also be diluted, transported, and transformed by physical, chemical, and biological processes (Ogunbiyi et al., 2024; Tansel, 2024), that could be one explanation of these negative associations. Moreover, terrestrial habitats use by lesser black-backed gulls are intensive agricultural areas, an activity where PFAS, including PFHxS and PFHpS, can be used as active pesticide ingredients (Donley et al., 2024). However, these positive and negative associations were not supported by any correlation of PFAS concentrations with the marine foraging index established from GPS-tracking, suggesting confounding factors involved or that statistical power may be too low. Half-lives
of δ¹³C, δ³S and δ¹⁵N in blood ranged from 16 to 19 days, 10 to 20 days, and 9 to 25 days, respectively (Arneson and MacAvoy, 2005; Carleton et al., 2008; Carleton and Rio, 2005; Lourenço et al., 2015). Thus, stable isotopes represent the habitat use during the breeding period, reflecting a larger temporal window than GPS-tracking. This temporal mismatches could blur potential relationships between habitat use inferred by isotopic values or GPS-tracking and blood PFAS concentrations. However, stable isotope values were highly correlated with the marine foraging index that was derived from GPS-tracking data (all *p* < 0.01; Fig. S4), confirming that stable isotopes are relevant indicator of recent habitat use.

The associations between PFAS concentrations and foraging ecology for lesser black-backed gulls contrasted with those reported for the herring gulls. These interspecies differences could be explained by the different marine habitats used, herring gulls only forage in coastal habitats while lesser black-backed gulls foraged in both coastal and offshore habitats. Coastal environments can be contaminated by PFAS through river inputs (Schmidt et al., 2019; Tansel, 2024), including the Sèvre Niortaise, the Seudre or the Charente estuaries in the study area (Munschy et al., 2019, 2013; Serre et al., 2025). PFAS concentrations in seawater and sediments are reported to be influenced by physicochemical and oceanographic proprieties (i.e., salinity, organic matter, turbidity, and currents) that could lead to different contamination in coastal and offshore environments and the apex predators related to these marine foraging habitats (Li et al., 2024; Munoz et al., 2017b; Ogunbiyi et al., 2024). However, we did not detect any significant correlation between PFAS concentrations and the use of coastal vs. offshore habitats (Supplementary Information 4). According to GPS-tracks, herring gulls and lesser black-backed gulls foraged in different terrestrial habitats (urban and landfill areas and fields, respectively) that may explain the interspecies differences observed in PFAS concentrations and associations with trophic ecology proxies. Additional ecotoxicological studies of abiotic (water or soil) and other biotic matrices, including prey in the different habitats, appear necessary to better understand the distribution of PFAS in terrestrial, coastal, and marine habitats.
Great black-backed gulls at Isle of Ré use the coastal environments and feed at high trophic level (Jouanneau et al., 2022; Fig. 3). Low inter-individual variability in isotopic values in this species could explain the absence of associations between isotopic values and blood concentrations of multiple PFAS. Interestingly, this coastal species showed high concentrations of PFCAs (Sebastiano et al., 2021), supporting further that the coastal environment could be a strong source of contamination for these compounds.

### PFAS concentrations and other intrinsic or extrinsic drivers

Our study highlighted that associations between PFAS and foraging ecology were species dependent. These interspecific variations seemed partially explained by the differences in use of marine resources, as we discussed earlier, and other drivers are also certainly involved. For example, the associations between blood PFAS concentrations and stable isotope values sometimes differed between males and females, especially for lesser black-backed gulls. Sex-specific foraging ecology could be one explanation, as females used more coastal habitats than males (Fig. 3B), which is consistent with a previous study on this species (Camphuysen et al., 2015). However, for the association between PFAS concentrations and the marine foraging index in lesser black-backed gulls, sex had a marginal effect, suggesting caution in driving conclusions. As previously proposed by Roscales et al., (2019), sexual and species differences in metabolic capabilities may also be a significant factor in the intra- and interspecies differences observed, but the close taxonomic affiliation of the three species in our study suggest further investigations. Gulls are income breeders (Hobson, 2006), thus assessing PFAS burden during the incubation period should reflect recent and local exposure. In plasma, the half-live of PFAS vary from several days (13 to 20 days for PFOS and 11 days for PFOA in avian model species, Newsted et al., 2007; Yoo et al., 2009), to several months (125 days for PFOS in chickens), or even several years for humans (Dawson et al., 2023). PFCAs are often reported to show much shorter half-lives in the plasma compared to PFOS, related to efficient elimination (Drew et al., 2022; Yeung et al., 2009; Yoo et al., 2009). Consequently, depending on the type of PFAS,
plasma concentrations can reflect recent dietary uptake, but also longer-term exposure as blood acts also as a significant reservoir for some long half-lived PFAS (Yeung et al., 2009; Yoo et al., 2009).

PFAS concentrations in plasma could thus be influenced by the habitat use and the diet of gulls several months before the study (e.g., wintering period, Léandri-Breton et al., 2024). Herring gulls and great black-backed gulls in this colony were mostly considered as resident species, with only restricted migratory movements along the French Atlantic coasts during winter (unpublished data). On the contrary, the lesser black-backed gulls migrate further south on the Iberian Peninsula, reaching as far as North Africa (unpublished data) where they could be exposed to additional sources of PFAS and thus making relationships between PFAS concentrations and foraging ecology during the breeding season less apparent. Tracking winter migration and feathers sampling, representative of concentrations during moulting, could also provide useful temporal and spatial information for studying the spatial contribution to inter- and intra-species differences in PFAS contamination (Léandri-Breton et al., 2024).

## 411 CONCLUSION

Our study shows that the concomitant use of stable isotope analyses and biologging can be useful to better understand inter- and intra-species differences in PFAS contamination and specifically suggests that high trophic position and the use of coastal foraging habitats, can lead to higher PFCAs contamination. The results obtained also highlight that the influence of trophic ecology and foraging habitat on PFAS exposure in wildlife can differ between species, sexes, and compounds.

Future studies mixing biologging and stable isotopes should include a variety of marine habitats (coastal, neritic, pelagic) and foraging tactics (diving, surface feeding) used both during the breeding and wintering seasons, as PFAS distribution is likely to differ seasonally, between habitats and the prey using these habitats.

421

422

423
424 **AUTHORS INFORMATION**

425 Corresponding Authors

426 *E-mail: david.rozen-rechels@sorbonne-universite.fr and prescillia.lemesle@cebc.cnrs.fr

427

428 **CRediT authorship contribution statement**

429 **David Rozen-Rechels:** Conceptualization, Methodology, Investigation, Formal analysis, Writing – original draft, Writing – review & editing, Visualization. **Prescillia Lemesle:** Methodology, Writing – original draft, Writing – review & editing, Visualization. **William Jouanneau:** Investigation, Formal analysis, Writing – review & editing. **Manrico Sebastiano:** Investigation, Writing – review & editing. **Stephanie M. Harris:** Formal analysis, Writing – Review & Editing. **Pierre Blévin:** Investigation, Writing – Review & Editing. **Frédéric Angelier:** Investigation, Writing – Review & Editing. **Julien Gernignon:** Investigation, Methodology, Resources. **Jean-Christophe Lemesle:** Investigation, Methodology, Resources. **Frédéric Robin:** Methodology, Writing – review & editing, Investigation, Resources. **Hélène Budzinski:** Writing – review & editing, Resources. **Pierre Labadie:** Writing – review & editing, Resources. **Paco Bustamante:** Resources, Writing – Review & Editing. **Olivier Chastel:** Conceptualization, Investigation, Resources, Writing – review & editing, Supervision, Funding acquisition, Project Administration.

441

442 **ASSOCIATED CONTENT**

443 Supporting Information

444 **Data Availability Statement**

445 Analyses reported in this article can be reproduced using the data and scripts provided at Zenodo (doi: XXX).

447

448 **ACKNOWLEDGMENTS**

449 This work has received approval for research ethics from the French Animal Ethic Committee (authorization number: APAFIS #15629-2019032823161213) and the Center for Research on Bird Population Biology (personal program n°533), certificate of approval is available upon request. This work was funded by the MULTISTRESS project (Région Nouvelle Aquitaine) and by the Agence Nationale de la Recherche: project ToxSeaBird (ANR-21-CE34-0019 to OC). PL and WJ were funded by the project ToxSeaBird. This work was supported by the PARC partnership (WP4) funded by the
European Union through the Grant 101057014. Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the EU or the European Research Executive Agency; neither the EU nor the granting authority can be held for them. GPS loggers were financed by the FEDER Nouvelle Aquitaine. We thank the plateform « Analyses Biologiques du CEBC », and especially Cécile Ribout for her expertise and her technical help in conducting sex analyses. We are grateful to Gaël Guillou from the platform « Analyses Isotopiques » of LIENSs for running the stable isotope analyses. We thank the CPER (Contrat de Plan Etat-Région) and the FEDER (Fonds Européen de Développement Régional) for funding the IRMS of LIENSs laboratory. PB is an honorary member of the IUF (Institut Universitaire de France). The authors are grateful to the anonymous reviewers who provided valuable comments on the manuscript.

## REFERENCES

466

467 Alfaro Garcia, L.A., Descamps, S., Herzke, D., Chastel, O., Carravieri, A., Cherel, Y., Labadie, P., Budzinski, H., Munoz, G., Bustamante, P., Polder, A., Gabrielsen, G.W., Bustnes, J.O., Borgå, K., 2022. Bioaccumulation of Per and Polyfluoroalkyl Substances in Antarctic Breeding South Polar Skuas (Catharacta maccormicki) and Their Prey. Front. Mar. Sci. 9.

471 Ask, A.V., Jenssen, B.M., Tartu, S., Angelier, F., Chastel, O., Gabrielsen, G.W., 2021. Per- and Polyfluoroalkyl Substances Are Positively Associated with Thyroid Hormones in an Arctic Seabird. Environ. Toxicol. Chem. 40, 820–831. https://doi.org/10.1002/etc.4978

474 Baak, J.E., Provencher, J.F., Mallory, M.L., Elliott, K.H., 2024. Spatial ecotoxicology: what we know about the relationship between avian movements and contaminant levels. Environ. Rev. 32, 315–333. https://doi.org/10.1139/er-2023-0101

477 Blévin, P., Angelier, F., Tartu, S., Bustamante, P., Herzke, D., Moe, B., Bech, C., Gabrielsen, G.W., Bustnes, J.O., Chastel, O., 2017a. Perfluorinated substances and telomeres in an Arctic seabird: Cross-sectional and longitudinal approaches. Environ. Pollut. 230, 360–367. https://doi.org/10.1016/j.envpol.2017.06.060

481 Blévin, P., Tartu, S., Ellis, H.I., Chastel, O., Bustamante, P., Parenteau, C., Herzke, D., Angelier, F., Gabrielsen, G.W., 2017b. Contaminants and energy expenditure in an Arctic seabird: Organochlorine pesticides and perfluoroalkyl substances are associated with metabolic rate in a contrasted manner. Environ. Res. 157, 118–126. https://doi.org/10.1016/j.envres.2017.05.022

485 Borgå, K., Fisk, A.T., Hoekstra, P.F., Muir, D.C.G., 2004. Biological and chemical factors of importance in the bioaccumulation and trophic transfer of persistent organochlorine contaminants in arctic marine food webs. Environ. Toxicol. Chem. 23, 2367–2385. https://doi.org/10.1897/03-518

488 Buck, R.C., Franklin, J., Berger, U., Conder, J.M., Cousins, I.T., de Voogt, P., Jensen, A.A., Kannan, K., Mabury, S.A., van Leeuwen, S.P., 2011. Perfluoroalkyl and polyfluoroalkyl substances in the environment: Terminology, classification, and origins. Integr. Environ. Assess. Manag. 7, 513–541. https://doi.org/10.1002/ieam.258

492 Burger, A.E., Shaffer, S.A., 2008. Perspectives in Ornithology Application of Tracking and Data-Logging Technology in Research and Conservation of Seabirds. The Auk 125, 253–264. https://doi.org/10.1525/auk.2008.1408

495 Bustnes, J.O., Bårdsen, B.J., Herzke, D., Johnsen, T.V., Eulaers, I., Ballesteros, M., Hanssen, S.A., Covaci, A., Jaspers, V.L.B., Eens, M., Sonne, C., Halley, D., Moum, T., Nøst, T.H., Erikstad, K.E., Ims, R.A., 2013. Plasma concentrations of organohalogenated pollutants in predatory bird nestlings: Associations
498 to growth rate and dietary tracers. Environ. Toxicol. Chem. 32, 2520-2527.

499 https://doi.org/10.1002/etc.2329

500 Camphuysen, K.C.J., Shamoun-Baranes, J., van Loon, E.E., Bouten, W., 2015. Sexually distinct foraging

501 strategies in an omnivorous seabird. Mar Biol 162, 1417-1428. https://doi.org/10.1007/s00227-015-

502 2678-9

503 Carravieri, A., Burthe, S.J., de la Vega, C., Yonehara, Y., Daunt, F., Newell, M.A., Jeffreys, R.M., Lawlor,

504 A.J., Hunt, A., Shore, R.F., Pereira, M.G., Green, J.A., 2020. Interactions between Environmental Contami-

505 nants and Gastrointestinal Parasites: Novel Insights from an Integrative Approach in a Marine Predator. En-

506 viron. Sci. Technol. 54, 8938-8948. https://doi.org/10.1021/acs.est.0c03021

507 Cheng, Y., Liu, Yuanyuan, Zhao, Y., Zheng, D., Feng, K., Cheng, J., Chu, J., Liu, Yang, Sun, J., 2025. Vari-

508 ation in dietary preference related the per- and polyfluoroalkyl substance exposure in two sympatric

509 seabird species from the Yellow Sea, China. J. Hazard. Mater. 495, 138764.

510 https://doi.org/10.1016/j.jhazmat.2025.138764

511 Chételat, J., Ackerman, J.T., Eagles-Smith, C.A., Hebert, C.E., 2020. Methylmercury exposure in wildlife: A

512 review of the ecological and physiological processes affecting contaminant concentrations and their

513 interpretation. Sci. Total Environ. 711, 135117. https://doi.org/10.1016/j.scitotenv.2019.135117

514 Colomer-Vidal, P., Bertolero, A., Alcaraz, C., Garreta-Lara, E., Santos, F.J., Lacorte, S., 2022. Distribution

515 and ten-year temporal trends (2009-2018) of perfluoroalkyl substances in gull eggs from Spanish

516 breeding colonies. Environ. Pollut. 293, 118555. https://doi.org/10.1016/j.envpol.2021.118555

517 Conder, J.M., Hoke, R.A., Wolf, W. de, Russell, M.H., Buck, R.C., 2008. Are PFCAs Bioaccumulative? A

518 Critical Review and Comparison with Regulatory Criteria and Persistent Lipophilic Compounds. En-

519 viron. Sci. Technol. 42, 995-1003. https://doi.org/10.1021/es070895g

520 Cordner, A., Brown, P., Cousins, I.T., Scheringer, M., Martinon, L., Dagorn, G., Aubert, R., Hosea, L.,

521 Salvidge, R., Felke, C., Tausche, N., Drepper, D., Liva, G., Tudela, A., Delgado, A., Salvatore, D.,

522 Pilz, S., Horel, S., 2024. PFAS Contamination in Europe: Generating Knowledge and Mapping Known

523 and Likely Contamination with "Expert-Reviewed" Journalism. Environ. Sci. Technol. 58, 6616-

524 6627. https://doi.org/10.1021/acs.est.3c09746

525 Costantini, D., Blévin, P., Bustnes, J.O., Esteve, V., Gabrielsen, G.W., Herzke, D., Humann-Guilleminot, S.,

526 Moe, B., Parenteau, C., Récapet, C., Bustamante, P., Chastel, O., 2022. Integument carotenoid-based

527 colouration reflects contamination to perfluoroalkyl substances, but not mercury, in arctic black-leg-

528 ged kittwakes. Front. Ecol. Evol. 10, 952765. https://doi.org/10.3389/fevo.2022.952765

529 De Silva, A.O., Armitage, J.M., Bruton, T.A., Dassuncao, C., Heiger-Bernays, W., Hu, X.C., Kärrman, A.,

530 Kelly, B., Ng, C., Robuck, A., Sun, M., Webster, T.F., Sunderland, E.M., 2021. PFAS Exposure Path-

531 ways for Humans and Wildlife: A Synthesis of Current Knowledge and Key Gaps in Understanding.

532 Environ. Toxicol. Chem. 40, 631-657. https://doi.org/10.1002/etc.4935

533 DeWitt, J.C. (Ed.), 2015. Toxicological Effects of Perfluoroalkyl and Polyfluoroalkyl Substances, Molecular

534 and Integrative Toxicology. Springer International Publishing, Cham. https://doi.org/10.1007/978-3-

535 319-15518-0

536 Donley, N., Cox, C., Bennett, K., Temkin, A.M., Andrews, D.Q., Naidenko, O.V., 2024. Forever Pesticides:

537 A Growing Source of PFAS Contamination in the Environment. Environ. Health Perspect. 132,

538 075003. https://doi.org/10.1289/EHP13954

539 Drew, R., Hagen, T.G., Champness, D., Sellier, A., 2022. Half-lives of several polyfluoroalkyl substances

540 (PFAS) in cattle serum and tissues. Food Addit. Contam. Part A 39, 320-340.

541 https://doi.org/10.1080/19440049.2021.1991004

542 Elliott, J.E., Elliott, K.H., 2013. Tracking Marine Pollution. Science 340, 556-558. https://doi.org/10.1126/sci-

543 ence.1235197

544 Fenton, S.E., Ducatman, A., Boobis, A., DeWitt, J.C., Lau, C., Ng, C., Smith, J.S., Roberts, S.M., 2021. Per-

545 and Polyfluoroalkyl Substance Toxicity and Human Health Review: Current State of Knowledge and

546 Strategies for Informing Future Research. Environ. Toxicol. Chem. 40, 606-630. https://doi.org/10.1002/etc.4890

547 https://doi.org/10.1002/etc.4890

548 Feranec, J., Soukup, T., Hazeu, G., Jaffrain, G., 2016. European Landscape Dynamics: CORINE Land Cover

549 Data. CRC Press.

550 Forero, M., Hobson, K., 2003. Using stable isotopes of nitrogen and carbon to study seabird ecology: Appli-

551 cations in the Mediterranean seabird community. Sci. Mar. 67.
552 Franke, A., Caelli, T., Hudson, R.J., 2004. Analysis of movements and behavior of caribou (Rangifer tarandus) using hidden Markov models. Ecol. Model. 173, 259-270.
553
554 https://doi.org/10.1016/j.ecolmodel.2003.06.004

555 Fridolfsson, A.-K., Ellegren, H., 1999. A Simple and Universal Method for Molecular Sexing of Non-Ratite Birds. J. Avian Biol. 30, 116. https://doi.org/10.2307/3677252

557 Gaines, L.G.T., 2023. Historical and current usage of per- and polyfluoroalkyl substances (PFAS): A literature review. Am. J. Ind. Med. 66, 353-378. https://doi.org/10.1002/ajim.23362

559 Gebbink, W.A., Letcher, R.J., Burgess, N.M., Champoux, L., Elliott, J.E., Hebert, C.E., Martin, P., Wayland, M., Weseloh, D.V.C., Wilson, L., 2011. Perfluoroalkyl carboxylates and sulfonates and precursors in relation to dietary source tracers in the eggs of four species of gulls (Larids) from breeding sites spanning Atlantic to Pacific Canada. Environ. Int. 37, 1175-1182. https://doi.org/10.1016/j.envint.2011.04.003

564 Guckert, M., Rupp, J., Nürenberg, G., Nödler, K., Koschorreck, J., Berger, U., Drost, W., Siebert, U., Wibbelt, G., Reemtsma, T., 2023. Differences in the internal PFAS patterns of herbivores, omnivores and carnivores - lessons learned from target screening and the total oxidizable precursor assay. Sci. Total Environ. 875, 162361. https://doi.org/10.1016/j.scitotenv.2023.162361

568 Hebert, C.E., Letcher, R.J., Cyr, F., Drake, C., 2022. Fatty acid ecological tracers highlight the role of diet in perfluoroalkyl acid contaminant exposure in eggs of an omnivorous bird. J. Gt. Lakes Res. 48, 1270-1277. https://doi.org/10.1016/j.jglr.2022.08.010

571 Hobson, K.A., 2006. Using stable isotopes to quantitatively track endogenous and exogenous nutrient allocations to eggs of birds that travel to breed.

573 Hobson, K.A., Piatt, J.F., Pitocchelli, J., 1994. Using Stable Isotopes to Determine Seabird Trophic Relationships. J. Anim. Ecol. 63, 786. https://doi.org/10.2307/5256

575 Hopkins, K.E., McKinney, M.A., Letcher, R.J., Fernie, K.J., 2023. The influence of environmental and ecological factors on the accumulation and distribution of short- and long-chain perfluoroalkyl acids in a mid-trophic avian insectivore. Environ. Pollut. 321, 121133. https://doi.org/10.1016/j.envpol.2023.121133

579 Humann-Guilleminot, S., Blévin, P., Gabrielsen, G.W., Herzke, D., Nikiforov, V.A., Jouanneau, W., Moe, B., Parenteau, C., Helfenstein, F., Chastel, O., 2024. PFAS Exposure is Associated with a Lower Spermatic Quality in an Arctic Seabird. Environ. Sci. Technol. 58, 19617-19626. https://doi.org/10.1021/acs.est.4c04495

583 Jang, M., Shim, W.J., Han, G.M., Ha, S.Y., Cho, Y., Kim, M., Hong, S.H., 2022. Spatial distribution and temporal trends of classical and emerging persistent organic pollutants (POPs) in black-tailed gull (Larus crassirostris) eggs from Korea. Sci. Total Environ. 845, 157244. https://doi.org/10.1016/j.scitotenv.2022.157244

587 Jouanneau, W., Léandri-Breton, D.-J., Corbeau, A., Herzke, D., Moe, B., Nikiforov, V.A., Gabrielsen, G.W., Chastel, O., 2021. A bad start in life? Maternal transfer of legacy and emerging Poly- and Perfluoroalkyl Substances to eggs in an arctic seabird. Environ. Sci. Technol. acs.est.1c03773. https://doi.org/10.1021/acs.est.1c03773

591 Jouanneau, W., Sebastiano, M., Rozen-Rechels, D., Harris, S.M., Blévin, P., Angelier, F., Brischoux, F., Ger-nigon, J., Lemesle, J.-C., Robin, F., Cherel, Y., Bustamante, P., Chastel, O., 2022. Blood mercury concentrations in four sympatric gull species from South Western France: Insights from stable isotopes and biologging. Environ. Pollut. 308, 119619. https://doi.org/10.1016/j.envpol.2022.119619

595 Kelly, B.C., Sun, J.M., McDougall, M.R.R., Sunderland, E.M., Gobas, F.A.P.C., 2024. Development and Evaluation of Aquatic and Terrestrial Food Web Bioaccumulation Models for Per- and Polyfluoroalkyl Substances. Environ. Sci. Technol. 58, 17828-17837. https://doi.org/10.1021/acs.est.4c02134

598 Léandri-Breton, D.-J., Jouanneau, W., Legagneux, P., Tarroux, A., Moe, B., Angelier, F., Blévin, P., Bråthen, V.S., Fauchald, P., Gabrielsen, G.W., Herzke, D., Nikiforov, V.A., Elliott, K.H., Chastel, O., 2024. Winter Tracking Data Suggest that Migratory Seabirds Transport Per- and Polyfluoroalkyl Substances to Their Arctic Nesting Site. Environ. Sci. Technol. 58, 12909-12920. https://doi.org/10.1021/acs.est.4c02661

603 Leat, E.H.K., Bourgeon, S., Eze, J.I., Muir, D.C.G., Williamson, M., Bustnes, J.O., Furness, R.W., Borgå, K., 2013. Perfluoroalkyl substances in eggs and plasma of an avian top predator, great skua (Stercorarius skua), in the north Atlantic. Environ. Toxicol. Chem. 32, 569-576. https://doi.org/10.1002/etc.2101
606 Lewis, A.J., Yun, X., Spooner, D.E., Kurz, M.J., McKenzie, E.R., Sales, C.M., 2022. Exposure pathways and bioaccumulation of per- and polyfluoroalkyl substances in freshwater aquatic ecosystems: Key considerations. Sci. Total Environ. 822, 153561. https://doi.org/10.1016/j.scitotenv.2022.153561

609 Li, L., Han, T., Li, B., Bai, P., Tang, X., Zhao, Y., 2024. Distribution Control and Environmental Fate of PFAS in the Offshore Region Adjacent to the Yangtze River Estuary—A Study Combining Multiple Phases Analysis. Environ. Sci. Technol. 58, 15779–15789. https://doi.org/10.1021/acs.est.4c03985

612 Ma, T., Wu, P., Wang, L., Li, Q., Li, X., Luo, Y., 2023. Toxicity of per- and polyfluoroalkyl substances to aquatic vertebrates. Front. Environ. Sci. 11. https://doi.org/10.3389/fenvs.2023.1101100

614 Ma, T., Ye, C., Wang, T., Li, X., Luo, Y., 2022. Toxicity of Per- and Polyfluoroalkyl Substances to Aquatic Invertebrates, Planktons, and Microorganisms. Int. J. Environ. Res. Public. Health 19, 16729. https://doi.org/10.3390/ijerph192416729

617 Melnes, M., Gabrielsen, G.W., Herzke, D., Sagerup, K., Jenssen, B.M., 2017. Dissimilar effects of organohalogenated compounds on thyroid hormones in glaucous gulls. Environ. Res. 158, 350–357. https://doi.org/10.1016/j.envres.2017.06.007

620 Michelot, T., Langrock, R., Patterson, T.A., 2016. moveHMM: an R package for the statistical modelling of animal movement data using hidden Markov models. Methods Ecol. Evol. 7, 1308–1315. https://doi.org/10.1111/2041-210X.12578

623 Miller, A., Elliott, J.E., Elliott, K.H., Lee, S., Cyr, F., 2015. Temporal trends of perfluoroalkyl substances (PFAS) in eggs of coastal and offshore birds: Increasing PFAS levels associated with offshore bird species breeding on the Pacific coast of Canada and wintering near Asia. Environ. Toxicol. Chem. 34, 1799–1808. https://doi.org/10.1002/etc.2992

627 Miller, A., Elliott, J.E., Wilson, L.K., Elliott, K.H., Drouillard, K.G., Verreault, J., Lee, S., Idrissi, A., 2020. Influence of overwinter distribution on exposure to persistent organic pollutants (POPs) in seabirds, ancient murrelets (*Synthliboramphus antiquus*), breeding on the Pacific coast of Canada. Environ. Pollut. 259, 113842. https://doi.org/10.1016/j.envpol.2019.113842

631 Ministry of Ecological Transition, Biodiversity, Forests, Sea, and Fisheries, 2025. Info PFAS - Outil de visualisation des données nationales de surveillance des substances PFAS [WWW Document]. URL https://macarte.ign.fr/carte/HzWzr5/Info-PFAS# (accessed 8.1.25).

634 Munoz, G., Budzinski, H., Babut, M., Drouineau, H., Lauzent, M., Menach, K.L., Lobry, J., Selleslagh, J., Simonnet-Laprade, C., Labadie, P., 2017a. Evidence for the Trophic Transfer of Perfluoroalkylated Substances in a Temperate Macrotidal Estuary. Environ. Sci. Technol. 51, 8450–8459. https://doi.org/10.1021/acs.est.7b02399

638 Munoz, G., Budzinski, H., Labadie, P., 2017b. Influence of Environmental Factors on the Fate of Legacy and Emerging Per- and Polyfluoroalkyl Substances along the Salinity/Turbidity Gradient of a Macrotidal Estuary. Environ. Sci. Technol. 51, 12347–12357. https://doi.org/10.1021/acs.est.7b03626

641 Munschy, C., Bely, N., Pollono, C., Aminot, Y., 2019. Perfluoroalkyl substances (PFASs) in the marine environment: Spatial distribution and temporal profile shifts in shellfish from French coasts. Chemosphere 228, 640–648. https://doi.org/10.1016/j.chemosphere.2019.04.205

644 Munschy, C., Marchand, P., Venisseau, A., Veyrand, B., Zendong, Z., 2013. Levels and trends of the emerging contaminants HBCDs (hexabromocyclododecanes) and PFCs (perfluorinated compounds) in marine shellfish along French coasts. Chemosphere 91, 233–240. https://doi.org/10.1016/j.chemosphere.2012.12.063

648 Ogunbiyi, O.D., Massenat, N., Quinete, N., 2024. Dispersion and stratification of Per- and polyfluoroalkyl substances (PFAS) in surface and deep-water profiles: A case study of the Biscayne Bay area. Sci. Total Environ. 909, 168413. https://doi.org/10.1016/j.scitotenv.2023.168413

651 O'Hanlon, N.J., Clewley, G.D., Johnston, D.T., Thaxter, C.B., Langlois Lopez, S., Quinn, L.R., Boersch-Supan, P.H., Masden, E.A., Daunt, F., Wilson, J., Burton, N.H.K., Humphreys, E.M., 2025. Partial Niche Partitioning in Three Sympatric Gull Species Through Foraging Areas and Habitat Selection. Ecol. Evol. 15, e71577. https://doi.org/10.1002/ece3.71577

655 Padilha, J., de Carvalho, G.O., Willems, T., Lepoint, G., Cunha, L., Pessoa, A.R.L., Eens, M., Prinsen, E., Costa, E., Torres, J.P., Dorneles, P., Das, K., Bervoets, L., Groffen, T., 2022. Perfluoroalkylated compounds in the eggs and feathers of resident and migratory seabirds from the Antarctic Peninsula. Environ. Res. 214, 114157. https://doi.org/10.1016/j.envres.2022.114157

659 Padilha, J.A.G., Santos, S., Willems, T., Souza-Kasprzyk, J., Leite, A., Cunha, L.S.T., Costa, E.S., Pessôa, A.R., Eens, M., E, P., Torres, J.P.M., Das, K., Lepoint, G., Dorneles, P.R., Bervoets, L., Groffen, T.,
661 2024. Assessing the trophic ecology and migration on the exposure of cape petrels and Wilson's storm
662 petrels from Antarctica to perfluoroalkylated substances, trace and major elements. Environ. Res. 244,
663 117827. https://doi.org/10.1016/j.envres.2023.117827

664 Ricolfi, L., Taylor, M.D., Yang, Y., Lagisz, M., Nakagawa, S., 2024. Maternal transfer of per- and polyfluoro-
665 alkyl substances (PFAS) in wild birds: A systematic review and meta-analysis. Chemosphere 361,
666 142346. https://doi.org/10.1016/j.chemosphere.2024.142346

667 Robuck, A.R., Cantwell, M.G., McCord, J., Addison, L.M., Pfohl, M., Strynar, M.J., McKinney, R., Katz, 668 D.R., Wiley, D.N., Lohmann, R., 2020. Legacy and Novel Per- and Polyfluoroalkyl Substances 669 (PFAS) in Juvenile Seabirds from the US Atlantic Coast. Environ. Sci. Technol. 54, 12938-12948. 670 https://doi.org/10.1021/acs.est.0c01951

671 Robuck, A.R., McCord, J.P., Strynar, M.J., Cantwell, M.G., Wiley, D.N., Lohmann, R., 2021. Tissue-specific 672 distribution of legacy and novel per- and polyfluoroalkyl substances in juvenile seabirds. Environ. Sci. 673 Technol. Lett. 8, 457-462. https://doi.org/10.1021/acs.estlett.1c00222

674 Roscales, J.L., Vicente, A., Ryan, P.G., González-Solís, J., Jiménez, B., 2019. Spatial and Interspecies Heterogeneity in Concentrations of Perfluoroalkyl Substances (PFASs) in Seabirds of the Southern Ocean. 675 Environ. Sci. Technol. 53, 9855-9865. https://doi.org/10.1021/acs.est.9b02677

676 Schmidt, N., Fauvelle, V., Castro-Jiménez, J., Lajaunie-Salla, K., Pinazo, C., Yohia, C., Sempéré, R., 2019. 677 Occurrence of perfluoroalkyl substances in the Bay of Marseille (NW Mediterranean Sea) and the 678 Rhône River. Mar. Pollut. Bull. 149, 110491. https://doi.org/10.1016/j.marpolbul.2019.110491

680 Schymanski, E.L., Zhang, J., Thiessen, P.A., Chirsir, P., Kondic, T., Bolton, E.E., 2023. Per- and Polyfluoro-
681 alkyl Substances (PFAS) in PubChem: 7 Million and Growing. Environ. Sci. Technol. 57, 16918-
682 16928. https://doi.org/10.1021/acs.est.3c04855

683 Sebastiano, M., Angelier, F., Blévin, P., Ribout, C., Sagerup, K., Descamps, S., Herzke, D., Moe, B., Barbraud, 684 C., Bustnes, J.O., Gabrielsen, G.W., Chastel, O., 2020. Exposure to PFAS is Associated with Telomere 685 Length Dynamics and Demographic Responses of an Arctic Top Predator. Environ. Sci. Technol. 54, 686 10217-10226. https://doi.org/10.1021/acs.est.0c03099

687 Sebastiano, M., Jouanneau, W., Blévin, P., Angelier, F., Parenteau, C., Gernigon, J., Lemesle, J.C., Robin, F., 688 Pardon, P., Budzinski, H., Labadie, P., Chastel, O., 2021. High levels of fluoroalkyl substances and 689 potential disruption of thyroid hormones in three gull species from South Western France. Sci. Total 690 Environ. 765, 144611. https://doi.org/10.1016/j.scitotenv.2020.144611

691 Sebastiano, M., Jouanneau, W., Blévin, P., Angelier, F., Parenteau, C., Pallud, M., Ribout, C., Gernigon, J., 692 Lemesle, J.C., Robin, F., Pardon, P., Budzinski, H., Labadie, P., Chastel, O., 2023. Physiological ef- 693 fects of PFAS exposure in seabird chicks: A multi-species study of thyroid hormone triiodothyronine, 694 body condition and telomere length in South Western France. Sci. Total Environ. 901, 165920. 695 https://doi.org/10.1016/j.scitotenv.2023.165920

696 Serre, N., Singh, R.R., Munschy, C., Zalouk-Vergnoux, A., Aminot, Y., 2025. Suspect Screening of PFAS in 697 French Coastal Bivalves: In-Depth Detection and Annotation Using Aqueous Film-Forming Foams. 698 Environ. Sci. Technol. https://doi.org/10.1021/acs.est.5c05758

699 Sinclair, G.M., Long, S.M., Jones, O.A.H., 2020. What are the effects of PFAS exposure at environmentally 700 relevant concentrations? Chemosphere 258, 127340. https://doi.org/10.1016/j.chemo- 701 sphere.2020.127340

702 Tansel, B., 2024. Geographical characteristics that promote persistence and accumulation of PFAS in coastal 703 waters and open seas: Current and emerging hot spots. Environ. Chall. 14, 100861.
704 https://doi.org/10.1016/j.envc.2024.100861

705 Tartu, S., Gabrielsen, G.W., Blévin, P., Ellis, H., Bustnes, J.O., Herzke, D., Chastel, O., 2014. Endocrine and 706 Fitness Correlates of Long-Chain Perfluorinated Carboxylates Exposure in Arctic Breeding Black- 707 Legged Kittiwakes. Environ. Sci. Technol. 48, 13504-13510. https://doi.org/10.1021/es503297n

708 United Nations, 2020. Stockholm Convention on Persistent Organic Pollutants (POPs).

709 Wilkinson, B.P., Robuck, A.R., Lohmann, R., Pickard, H.M., Jodice, P.G.R., 2022. Urban proximity while 710 breeding is not a predictor of perfluoroalkyl substance contamination in the eggs of brown pelicans. 711 Sci. Total Environ. 803, 150110. https://doi.org/10.1016/j.scitotenv.2021.150110

712 Yeung, L.W.Y., Loi, E.I.H., Wong, V.Y.Y., Guruge, K.S., Yamanaka, N., Tanimura, N., Hasegawa, J., Yam-
713 ashita, N., Miyazaki, S., Lam, P.K.S., 2009. Biochemical Responses and Accumulation Properties of
714 Long-Chain Perfluorinated Compounds (PFOS/PFDA/PFOA) in Juvenile Chickens (Gallus gallus).
715 Arch. Environ. Contam. Toxicol. 57, 377-386. https://doi.org/10.1007/s00244-008-9278-3
716 Yoo, H., Guruge, K.S., Yamanaka, N., Sato, C., Mikami, O., Miyazaki, S., Yamashita, N., Giesy, J.P., 2009.

717 Depuration kinetics and tissue disposition of PFOA and PFOS in white leghorn chickens (Gallus gallus) administered by subcutaneous implantation. Ecotoxicol. Environ. Saf.

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<figure><img src="image_23.png" /><figcaption>**Fig 1.** Direction and significance of PC₁ scores in multivariate linear regressions to PFAS concentrations. A: herring gull (blue); B: lesser black-backed gull (yellow); C: great black-backed gull (red). PFAS are classified by chemical structure (sulfonic and carboxylic) and ordered by carbon chain length. The height of each bar represents $β_x$ of PC₁ (predicted linear coefficient) for PFAS X. If $β_x > 0$ (resp. < 0), then the concentration of PFAS X increases (resp. decreases) when PC₁ increases</figcaption></figure>
(resp. decreases) (see small panel). Error bars are standard errors. The stars represent the significance of the t-test comparing the difference of $\beta_x$ to 0: *: $0.05 \ge p > 0.01$; **: $0.01 \ge p > 0.001$; ***: $0.001 \ge p$, and their absence means no significance. Hatched and plain bars are for females and males, respectively. Note that the best model explaining variations in the PFAS concentrations in males great black-backed gulls is the null model.

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<figure><img src="image_24.png" /><figcaption>**Fig 2.** Relationships between PFAS concentrations and PC₁ related to stable isotopes values, with four representative PFAS (two carboxylic PFAS and two sulfonic PFAS) chosen as an example. A: PFUnDA; B: PFTrDA, C: PFHxS and D: L-PFOS as a function of PC₁. Higher PC₁ scores are related to higher stable isotopes values (carbon, sulphur and nitrogen). Each point represents an individual. Lines are predicted significant linear relationships between PFAS concentrations and PC₁ averaged per year. Colours indicate the species with European herring gull, lesser black-backed gull and great black-backed gull in blue, yellow and red, respectively. Line types and shape points are different for females and males, with dashed lines and circles for females and plain lines and triangles for males.</figcaption></figure>
A

<figure><img src="image_25.png" /></figure>

<figure><img src="image_26.png" /></figure>

Species

● Larus argentatus

● Larus fuscus

● Larus marinus

● Rivers

Habitat

● Coastal

● Offshore

● Terrestrial

<figure><img src="image_27.png" /></figure>

0 10 20 km

<figure><img src="image_28.png" /></figure>

B

● Terrestrial

● Coastal

● Offshore

EUROPEAN HERRING GULL

<figure><img src="image_29.png" /></figure>

male
female

<figure><img src="image_30.png" /></figure>

LESSER BLACK-BACKED GULL

<figure><img src="image_31.png" /></figure>

male
female

<figure><img src="image_32.png" /></figure>

GREAT BLACK-BACKED GULL

<figure><img src="image_33.png" /></figure>

male
female

<figure><img src="image_34.png" /></figure>

Foraging habitat (%)

103

<caption>Fig 3. A. Visualisation of the identified foraging sites for each species around the colony "Lilleau des Niges" in the Isle of Ré. Each point indicates a foraging site in the map. Each species is indicated by a colour with European herring gull, lesser black-backed gull, and great black-backed gull in blue, yellow, and red, respectively. Terrestrial, coastal and offshore habitats are indicated in brown, light blue and dark blue, respectively. B. Percent stacked barplots of the proportion of foraging sites in</caption>
791 different foraging habitats for each sex of the three species: the European herring gull (n = 17, 8 males

792 / 9 females), the lesser black-backed gull (n = 18, 10 males / 8 females) and the great black-backed

793 gull (n = 6, 3 males / 3 females). Percent in the stacked plots correspond to median proportions.

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<figure><img src="image_35.png" /><figcaption>Fig 4. Direction and significance of the marine foraging index coefficients in multivariate linear regressions to PFAS concentrations. A: herring gull (blue); B: lesser black-backed gull (yellow); Great black-backed gulls were not retained in this analysis due to low sample size (n= 6). PFAS are classified by chemical structure (sulfonic and carboxylic) and ordered by carbon chain length. The height of each bar represents βx of predicted linear coefficient of marine foraging index for PFAS X. If βx > 0 (resp. < 0), then the concentration of PFAS X increases (resp. decreases) when the marine foraging index increase (resp. decrease) (see small panel). Error bars are standard errors. The stars</figcaption></figure>
810 represent the significance of the t-test comparing the difference of $\beta_x$ to 0: *: 0.05 $\ge$ p > 0.01; **: 0.01 $\ge$ p > 0.001; ***: 0.001 $\ge$ p, and their absence means no significance. Hatched and plain bars are for females and males, respectively. Note that the best model explaining variations in PFAS concentrations is for panel A: the model with a marginal sex effect for herring gulls and for panel B: the null model for lesser black backed gulls.
<figure><img src="image_36.png" /><figcaption>Fig 5. Relationships between PFAS concentrations and the marine foraging index with four representative PFAS (two carboxylic PFAS and two sulfonic PFAS) chosen as an example. A: PFUnDA; B: PFTrDA, C: PFHxS and D: L-PFOS as a function of proportion of marine foraging sites. Each point represents an individual. Lines are predicted significant linear relationships between PFAS concentrations and PC₁. Colours indicate the species with European herring gull, lesser black-backed gull and great black-backed gull in blue, yellow and red, respectively. Raw values for great black backed gull individuals have been plotted for information despite the fact that we did not fit any model to relate them to the marine foraging index. Line types and shape points are different for fe- males and males, with dashed lines and circles for females and plain lines and triangles for males.</figcaption></figure>
**Highlights:**

* The influence of habitat use on PFAS contamination was studied in three gull species

* PFAS levels were combined with GPS tracking and stable isotopes (δ¹³C; δ³S, δ¹⁵N).

* Association between PFAS concentrations and habitat use was species-dependent.

* Coastal foraging habitat could be a source of PFAS contamination.
**Declaration of 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.

☐ The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

<figure><img src="image_37.png" /></figure>