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Rationale: Understanding the migration of marine animals is hindered by the limitations of traditional tracking methods. It is therefore crucial to develop alternative methods. Stable isotope‐based tracking has proven useful for this task, although it requires detailed isoscapes in the focal area. Here, we present predator‐based isoscapes of the coastal zone of the Patagonian Shelf Large Marine Ecosystem (PSLME), which offers a novel tool for geolocation. Methods: Whole‐blood samples from breeding Magellanic penguins nesting at 11 colonies were used to create δ15N and δ13C isoscapes. Isotopic values were assigned to random positions inside their corresponding foraging area. Spatial analysis and data interpolation resulted in δ15N and δ13C isoscapes for the coastal zone of the PSLME, which were validated through cross‐validation. Results: The isoscapes mean standard error ranged from 0.05 to 0.41 for δ15N and from 0.07 to 0.3 for δ13C, similar to the error range of the mass spectrometer used for measuring isotope ratios. Predictive surfaces reflected the latitudinal trends, with δ13C and δ15N values increasing northwards. δ13C values showed a strong latitudinal gradient, while δ15N values had two distinct domains, with higher values in the north. The error surface indicated the highest certainty within 130 km from the shore and within the reported Magellanic penguin foraging areas. Conclusions: Both isoscapes revealed strong spatial variation. The δ13C isoscape showed a latitudinal gradient, consistent with patterns in other oceans. The δ15N isoscape clearly separated northern and southern colonies, likely influenced by nitrogen sources. The error obtained fell within the measurement error ranges, adding credibility to the models. [ABSTRACT FROM AUTHOR]

The genetic identification of evolutionary significant units and information on their connectivity can be used to design effective management and conservation plans for species of concern. Despite having high dispersal capacity, several seabird species show population structure due to both abiotic and biotic barriers to gene flow. The Kelp Gull is the most abundant species of gull in the southern hemisphere. In Argentina it reproduces in both marine and freshwater environments, with more than 100,000 breeding pairs following a metapopulation dynamic across 140 colonies in the Atlantic coast of Patagonia. However, little is known about the demography and connectivity of inland populations. We aim to provide information on the connectivity of the largest freshwater colonies (those from Nahuel Huapi Lake) with the closest Pacific and Atlantic populations to evaluate if these freshwater colonies are receiving immigrants from the larger coastal populations. We sampled three geographic regions (Nahuel Huapi Lake and the Atlantic and Pacific coasts) and employed a reduced-representation genomic approach to genotype individuals for single-nucleotide polymorphisms (SNPs). Using clustering and phylogenetic analyses we found three genetic groups, each corresponding to one of our sampled regions. Individuals from marine environments are more closely related to each other than to those from Nahuel Huapi Lake, indicating that the latter population constitutes the first freshwater Kelp Gull colony to be identified as an evolutionary significant unit in Patagonia. [ABSTRACT FROM AUTHOR]

Many closely related seabirds nest in mixed colonies, and this association may result in interspecific interactions such as competition for common resources and kleptoparasitism. Trophic interactions were evaluated between the Kelp Gull (Larus dominicanus Lichtenstein, 1823) and Royal and Cayenne terns (Thalasseus maximus maximus (Boddaert, 1783) and Thalasseus sandvicensis eurygnathus (Saunders, 1876), respectively) nesting at a mixed-species colony in an area with high availability of recreational fishery waste for the opportunistic Kelp Gull. Diet analyses were based on gull chick stomach content samples and direct observations of food delivered to tern chicks in 2013 and 2014, complemented in 2014 with carbon and nitrogen stable isotope analysis of chick whole-blood samples. Main prey species of Kelp Gull chicks were Cynoscion guatucupa (Cuvier, 1830), a demersal species obtained from recreational fishery waste, Argentine anchovies (Engraulis anchoita Hubbs and Marini, 1935), and insects. Engraulis anchoita and Odontesthes spp. were the main prey of both tern species. Trophic niche and isotopic niche overlap between the Kelp Gull and Royal and Cayenne terns was low. Kelp Gull kleptoparasitism on Royal and Cayenne terns was [less than or equal to]2.5% and Key words: mixed-species colonies, trophic niche, kleptoparasitism, Kelp Gull, Larus dominicanus, Royal Tern, Thalasseus maximus maximus, Cayenne Tern, Thalasseus sandvicensis eurygnathus. De nombreux oiseaux marins étroitement apparentés nidifient dans des colonies mixtes, et cette association peut se traduire par différentes interactions d'espèces comme la concurrence pour des ressources partagées et le cleptoparasitisme. Nous avons évalué les interactions trophiques de goélands dominicains (Larus dominicanus Lichtenstein, 1823) et de sternes royales et de Cayenne (Thalasseus maximus maximus (Boddaert, 1783) et Thalasseus sandvicensis eurygnathus (Saunders, 1876), réspectivement) nidifiant dans une colonie mixte dans un secteur offrant une bonne disponibilitéde résidus de pêche sportive pour les goélands dominicains opportunistes. Les analyses des régimes alimentaires sont basées sur des échantillons de contenu stomacal de bébés goélands et des observations directes de la nourriture apportée aux bébés sternes en 2013 et 2014, auxquelles s'ajoutent des analyses d'isotopes stables du carbone et de l'azote d'échantillons de sang entier d'oisillons réalisées en 2014. Les principales proies des goélands dominicains étaient le bar Cynoscion guatucupa (Cuvier, 1830), un poisson démersal obtenu de résidus de pêche sportive, l'anchois d'Argentine (Engraulis anchoita Hubbs et Marini, 1935) et des insectes. Engraulis anchoita et Odontesthes spp. étaient les principales proies des deux espèces de sternes. Le chevauchement des niches trophiques et isotopiques des goélands dominicains et des sternes royales et de Cayenne était faible. Les taux de cleptoparasitisme de goélands dominicains sur des sternes royales et de Cayenne étaient de [inférieur ou égal à]2,5% et Mots-clés : colonies mixtes, niche trophique, cleptoparasitisme, goéland dominicain, Larus dominicanus, sterne royale, Thalasseus maximus maximus, sterne de Cayenne, Thalasseus sandvicensis eurygnathus., Introduction Many seabird species nest in mixed colonies of two or more species, often closely related, and this spatial and temporal association may result in several negative and positive interspecific [...]