Individual diet specialization occurs in many populations of generalist predators, with specific individuals developing specialist strategies in their feeding behaviour. Intraspecific resource partitioning is hypothesised to be common amongst species in higher trophic levels where competition for resources is intense, and a key driver in breeding success and community structure. Though well-studied in other predators, there is sparse data on ecological specialization in raptors, which are important drivers of community and trophic structure. In this study, the breeding season diet of an insular population of peregrine falcons (Falco peregrinus) was determined from indirect analysis of prey remains collected over three years. An unexpected result was the high proportion of large gulls (Laridae), of the genus Larus, in the diet of two breeding pairs of peregrines. Large gulls made up 18.44% by frequency of total prey recorded and 30.81% by biomass. Herring gulls (Larus argentatus) were the most common large gull prey, with immatures most frequent (67.95%) compared to adults (19.23%). Overall, most gulls predated were immatures (80.77%). Frequency of predation varied between breeding pairs and months, but was consistent over the three years. Most gulls were taken in April (37.17%), followed by May (19.23%), with a smaller peak of immature herring gulls taken in August and September. The pattern of regular predation by peregrines on large gulls is a new observation with important implications for understanding individual diet specialization in raptors, and its effect on bird populations and community structure.Abstrakt: Individuálna potravná špecializácia sa vyskytuje v mnohých populáciách generalistických predátorov, kde si jedince vytvárajú špecializované stratégie v ich potravnom správaní. Predpokladá sa, že vnútrodruhové prerozdeľovanie zdrojov je bežné pre druhy na vyšších trofických úrovniach, kde je intenzívna konkurencia o zdroje potravy a tak je hlavný faktor hniezdneho úspechu a štruktúry spoločenstva. Hoci je ekologická špecializácia dobre študovaná u iných predátorov, údajov o dravých vtákov, dôležitých činiteľov ovplyvňujúcich trofickú štruktúru spoločenstva, je málo. Potrava sokola sťahovavého (Falco peregrinus) z ostrovnej populácie počas hniezdnej sezóny sa v tejto štúdii určila nepriamou analýzou zvyškov koristi zbieraných počas troch rokov. Neočakávaným výsledkom bol veľký podiel veľkých čajok (Laridae) z rodu Larus v potrave dvoch hniezdnych párov sokola. Frekvencia výskytu veľkých čajok v koristi bola 18,44 % a 30,81 % jej celkovej biomasy. Najčastejšie lovenou veľkou čajkou bola čajka striebristá (Larus argentatus), mladé jedince častejšie (67,95 %) než dospelé (19,23 %). Celkovo, najčastejšie boli predované mladé jedince (80,77 %). Frekvencia predácie varírovala medzi hniezdiacimi pármi a mesiacmi, avšak bola zhodná počas troch rokov. Väčšina čajok bola ulovená v apríli (37,17 %) a v máji (19,23 %), s menším nárastom početnosti nedospelých jedincov čajky striebristej ulovených v augus...

Globally, habitat loss or degradation is a major threat to many species, and those with specific habitat requirements are particularly vulnerable. Many species of wading birds (Charadrii) are dependent upon intertidal sites to feed, but, as a result of anthropogenic pressures, the prey landscape has changed at many estuaries. Behavioral adaptations may be able to buffer these changes. In this study over multiple seasons, we aimed to investigate the foraging behaviors of wintering Eurasian oystercatchers in the Exe Estuary where mussel beds, the preferred prey at this site, have almost disappeared in the last decade. From 2018 to 2021, GPS tracking devices were deployed on 24 oystercatchers, and the foraging locations of adults, sub-adults, and juveniles were determined. Of the 12 birds tracked over multiple winter periods, 10 used the same foraging home ranges but a juvenile and sub-adult changed locations interannually. The dominant prey species at key foraging sites were assessed, and we found that younger birds were more likely to visit sites with lower quality prey, likely due to being at a competitive disadvantage, and also to explore sites further away. Individuals were generally consistent in the areas of the estuary used in early and late winter, and over 90% of locations were recorded in the protected area boundary, which covers the sand and mudflats of the Exe. These findings suggest high specificity of the current protected area for oystercatchers in the Exe Estuary, although, if the prey landscape continues to decline, younger individuals may provide the potential for adaptation by finding and foraging at additional sites. Continued monitoring of individual behavior within populations that are facing dramatic changes to their prey is essential to understand how they may adapt and to develop suitable management plans to conserve threatened species.