Spatio-temporal trends in the predation of large gulls by peregrine falcons (Falco peregrinus) in an insular breeding population

Abstract

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...

Diet specialization in an insular population of coastal Peregrine Falcons

“…We identified prey species from Brown et al . (2003) and previous experience (Sutton 2015a, 2016; Sutton et al . 2017).…”

“…Remains observed on inaccessible feeding areas were recorded using a Digital Single Lens Reflex (DSLR) camera for later analysis and the location recorded indirectly using Google Earth (https://earth.google.com/web/) software. We identified prey species from Brown et al (2003) and previous experience (Sutton 2015a(Sutton , 2016Sutton et al 2017). Avian prey remains from Peregrines are readily identified.…”

“…Recent dietary assessments from Lundy, an island in the Bristol Channel between England and Wales, indicate that seabirds, including Manx Shearwater Puffinus puffinus and Herring Gull Larus argentatus, are the primary food source for the resident Peregrines (Sutton 2016;Sutton et al 2017). Lundy was historically one of many important seabird colonies lying off the south west coast of the British Isles (Brown et al 2011).…”

Diet Specialization in an Insular Population of Coastal Peregrine Falcons

“…Remains observed on inaccessible feeding areas were recorded using a Digital Single Lens Reflex (DSLR) camera for later analysis and the location recorded indirectly using Google Earth (https://earth.google.com/web/) software. We identified prey species from Brown et al (2003) and previous experience (Sutton 2015a, 2016, Sutton et al 2017). Avian prey remains from Peregrines are readily identified.…”

“…Recent dietary assessments from Lundy, an island in the Bristol Channel between England and Wales, indicate that seabirds, including Manx Shearwater Puffinus puffinus and European Herring Gull Larus argentatus , are the primary food source for the resident Peregrines (Sutton 2016, Sutton et al 2017). Lundy was historically one of many important seabird colonies lying off the south west coast of the British Isles (Brown et al 2011).…”