Varying foraging patterns in response to competition? A multicolony approach in a generalist seabird

Abstract

Reducing resource competition is a crucial requirement for colonial seabirds to ensure adequate self‐ and chick‐provisioning during breeding season. Spatial segregation is a common avoidance strategy among and within species from neighboring breeding colonies. We determined whether the foraging behaviors of incubating lesser black‐backed gulls (Larus fuscus) differed between six colonies varying in size and distance to mainland, and whether any differences could be related to the foraging habitats visited. Seventy‐nine incubating individuals from six study colonies along the German North Sea coast were equipped with GPS data loggers in multiple years. Dietary information was gained by sampling food pellets, and blood samples were taken for stable isotope analyses. Foraging patterns clearly differed among and within colonies. Foraging range increased with increasing colony size and decreased with increasing colony distance from the mainland, although the latter might be due to the inclusion of the only offshore colony. Gulls from larger colonies with consequently greater density‐dependent competition were more likely to forage at land instead of at sea. The diets of the gulls from the colonies furthest from each other differed, while the diets from the other colonies overlapped with each other. The spatial segregation and dietary similarities suggest that lesser black‐backed gulls foraged at different sites and utilized two main habitat types, although these were similar across foraging areas for all colonies except the single offshore island. The avoidance of intraspecific competition results in colony‐specific foraging patterns, potentially causing more intensive utilization of terrestrial foraging sites, which may offer more predictable and easily available foraging compared with the marine environment.

Intercolony variations in movement patterns and foraging behaviors among herring gulls (Larus argentatus) breeding in the eastern Wadden Sea

“…Inter‐ and/or intraspecific competition (Corman et al., 2016; Hamilton, Gilbert, Heppner, & Planck, 1967) may thus be an important factor driving decisions on where to forage. Corman et al.…”

“…Corman et al. (2016) demonstrated low inter‐ and intracolonial overlaps in foraging behavior in lesser black‐backed gulls. In our study, gulls from Langeness were the most flexible in terms of habitat choice although the sample size of tagged birds from this colony was very low.…”

“…The same could be supposed for herring gulls breeding closer to the coast. Foraging trips heading to the west might not be an option for gulls from Oland, because of intraspecific competition from neighboring colonies (Corman et al., 2016). …”

“…Similar observations have been made for lesser black‐backed gulls ( Larus fuscus ), previously known as a predominantly marine species, but which is increasingly adopting a dual foraging strategy utilizing both marine and terrestrial habitats (Isaksson, Evans, Shamoun‐Baranes, & Akesson, 2016), possibly as a result of food depletion at sea (Garthe et al., 2016; Votier et al., 2004). Furthermore, a multi‐colony study of lesser black‐backed gulls based on individual movement patterns revealed that foraging behaviors also differed between neighboring colonies (Corman, Mendel, Voigt, & Garthe, 2016). …”

Short distance migrants travel as far as long distance migrants in lesser black‐backed gulls Larus fuscus

“…One individual observed in this study showed that at least some individual gulls can have alternative migration strategies within their life span. Previously abundant but already declining anthropogenic resources utilized by gulls, such as human refuse and fishery discards (Camphuysen , Camphuysen et al , Corman et al ), are likely to decline further due to changes in EU legislation (Bicknell et al ); whether or not individuals can adapt to these changes within their life span will highly depend on their behavioural plasticity and ability to adapt their foraging or migration strategies accordingly. In order to understand the consequences of different migration strategies and changes within the key resources, they should be considered within the context of the annual cycle and life history of an individual (Harrison et al , Marra et al ).…”