Annual and seasonal consistency in the feeding ecology of an opportunistic species, the yellow-legged gull Larus michahellis

Abstract

This study investigated the extent to which the plasticity of a generalist, opportunistic species allows individuals to shift their feeding ecology and foraging niche, throughout the annual cycle, and between 2 years of contrasting diet and oceanographic conditions during the breeding season. The spatio-temporal variations in the foraging niche of an overpopulated gull species -the yellow-legged gull Larus michahellis population at Berlenga Island (Portugal)were assessed using blood (plasma and cells) and different feathers for stable isotope analyses (δ 13 C and δ 15 N) from 52 breeding adults in 2 consecutive years (2011 and 2012). In addition, GPS loggers were deployed on 11 individuals (and removed after several foraging trips) to infer the foraging behaviour of this species during the incubation period. Results suggest inter-annual differences in the feeding ecology and foraging behaviour of birds during the breeding season that were associated with the availability of food resources around the colony. Despite the high feeding plasticity and opportunistic behaviour of yellow-legged gulls, individual birds exhibited shortand long-term consistency in their feeding ecology, with exception of the period between winter and pre-laying. Our results support the hypothesis that individual feeding preferences throughout most of the annual cycle are an intrinsic characteristic of this population, and potentially of related opportunistic and generalist species.

Assessment of contaminant levels and trophic relations at a World Heritage Site by measurements in a characteristic shorebird species

“…We therefore hypothesised that contaminant levels would be higher with increasing values of δ 15 N; furthermore, we hypothesised higher contaminant levels with increasing values of δ 13 C as those would indicate a higher degree of foraging in the potentially more contaminated marine environment (Fry, 2006;Inger and Bearhop, 2008;Ceia et al, 2014). However, we found no indication of such a relationship in either feathers or blood.…”

“…15 N values in coastal birds such as oystercatchers indicate that they feed on prey originating from higher trophic levels, while low δ 13 C values indicate prey of terrestrial origin (Inger and Bearhop, 2008;Ceia et al, 2014). We found higher δ 15 N values and lower δ 13 C in feathers, compared with serum and blood cells, at the Oland site.…”

“…We also examined the relationship between contaminant levels in feathers and those in blood, as suggested by Jaspers et al (2007Jaspers et al ( , 2008 for other bird species. (3) Trophic position of consumers such as birds and the origin of prey can be investigated by analysis of stable isotopes (Inger and Bearhop, 2008 Fry, 2006;Inger and Bearhop, 2008;Ceia et al, 2014). We therefore aimed to relate levels of different types of pollutants to the feeding habits of the birds (Jaspers et al, 2007).…”

Shifting individual habitat specialization of a successful predator living in anthropogenic landscapes

“…This gull is also considered a pest within urban, agricultural and coastal areas (Vidal et al 1998). Based on previous information (Ceia et al 2014, Tyson et al 2015, Ceia & Ramos 2015, we hypothesized that yellow-legged gulls present a significant level of individual differences in habitat use. Specifically, we predicted that individuals within the population would show niche segregation with respect to habitat use.…”

“…Thus, taking into account the individual component should allow for a better understanding of ecological processes. In addition, knowing the degree of individual specialization in winning species that negatively affect human or wildlife health may help to implement more effective management actions (Sanz-Aguilar et al 2009, Bowen & Lidgard 2013, Ceia et al 2014.…”