Autor(es):
Pedro, Patricia I. 
; Ramos, J. A. ; Neves, Verónica C. ; Paiva, Vitor H.
Data: 2013
Identificador Persistente: http://hdl.handle.net/10316/25593
Origem: Estudo Geral - Universidade de Coimbra
Assunto(s): Azores; Trophic position; Diet; Plasticity; Refuse; Yellow-legged Gulls
Descrição
This study evaluates the trophic position of adult
Yellow-legged Gulls Larus michahellis atlantis resident in
the Azores archipelago in the past (1921–1928) and in the
present (2009–2010), and analyses the decadal variation in
the diet of breeding birds from the 1990s to the 2000s for
three main colonies (Topo Islet, Baixo Islet and Mistério da
Prainha). Using mixing models, we compared stable isotope
signatures of nitrogen and carbon in adult breast feathers
between birds from 1921 to 1928 (held in museum collections)
and 2009 to 2010, jointly with both isotopic signatures
of their main prey groups (fish, goose barnacles (Lepas
anatifera), seabirds, mammals and refuse). The diet of
breeding birds was analysed using pellets collected in
1989, 1995, 1996, 2004, 2009 and 2010. Stable isotopes
analysis (SIA) results were in accordance with the results
provided from the analysis of pellets, showing a relatively
recent and significant change in the diet of adult gulls. In
particular, SIA revealed a significant decrease in the trophic
position of Yellow-legged Gulls in the Azores, over the last
89 years in response to the decrease in the consumption of
seabirds and fish and, an increase in the consumption of
marine invertebrates (goose barnacles) and refuse. The analysis
of pellets confirmed the significant decrease in the fish
ingested, whereas the ingestion of lower trophic level prey (i.e. goose barnacles, mammals and refuse) increased. Both
methods reflect the feeding plasticity and opportunistic foraging
behavior of this species, and are in accordance with
patterns described for continental Europe. We acknowledge the support given by Fundação
para a Ciência e Tecnologia, Portugal, to Patricia Pedro (SFRH/BD/
40095/2007).
