Spatial foraging segregation by close neighbours in a wide-ranging seabird

Abstract

Breeding seabirds are central-place foragers and therefore exploit food resources most intensively nearer their colonies. When nesting aggregations are close to one another density-dependent competition is likely to be high, potentially promoting foraging segregation (i.e. neighbouring colonies may segregate to search for food in different areas). However, little is known about spatial segregation in foraging behaviour between closely adjacent colonies, particularly in species that are wide-ranging foragers. Here, we tested for foraging segregation between two sub-colonies of a wide-ranging seabird, Cory's shearwater Calonectris borealis, separated by only 2 km, on a small Island in the North Atlantic. During the 2010 chick-rearing period, 43 breeding adults of both sexes were simultaneously sampled at both sub-colonies. A GPS logger was deployed on each individual and removed after several foraging trips at sea. Blood samples (plasma and red blood cells) were collected from each tracked individual for stable isotope analysis. Results indicated partial spatial segregation between the two sub-colonies during local foraging trips (i.e. those of ≤1 day duration and 216 km from the colony) accounting for 84.2% of all trips recorded. The location of the breeding sub-colony influenced the direction of travel of birds during local trips resulting in sub-colony-specific foraging areas. Although the oceanographic conditions associated with the foraging range of the two sub-colonies differed, no differences were found in the habitat exploited and in their estimated diets. This suggests that birds concentrated their feeding activity in patches of similar habitat and prey during the chick-rearing period.

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

“…This suggests that LBBGs use segregated foraging sites in different habitats but that these sites showed similar prey availability within the two main foraging habitats (Ceia et al. ). However, dietary segregation might occur at the individual, rather than the colony level, as shown, e.g., for other gull species (Masello et al.…”

Individual-level Variation and Higher-level Interpretations of Space Use in Wide-ranging Species: An Albatross Case Study of Sampling Effects

“…A straightforward approach to reporting individual variation in movement within a tracking dataset is to conduct and report individual-level analyses, as illustrated recently by Ceia et al (2015), Young et al (2015), and in the present study ( Table 2; Figures 2, 3). While identifying the locations and areas of high use regions is more challenging to describe quantitatively from stacked individual contours, the degree of variation among individuals is clear.…”

Simultaneous multi-colony tracking of a pelagic seabird reveals cross-colony utilization of a shared foraging area

“…For each colony and period, the relationship between foraging trip maximum distance and duration was tested using generalized linear mixed models with duration as the dependent variable, maximum distance as a fixed effect, and individual bird as a random effect. Long-and short-distance trips were delineated by a 200 km maximum distance contour, a distance giving good separation between chick-provisioning and self-maintenance trips in this species (Shoji et al 2015) and similar to that used to define local foraging in the related Cory's shearwater (Ceia et al 2015). An additional 6 very long-range trips into the At lantic beyond the continental shelf edge (see Fig.…”