Scale‐dependent habitat use in a long‐ranging central place predator

Abstract

1 It is predicted that the movements of foraging animals are adjusted to the hierarchical spatial distribution of resources in the environment, and that decisions to modify movement in response to heterogeneous resource distribution are scale-dependent. Thus, controlling for spatial scales of interaction with environment is critical for a better understanding of habitat selection, which is likely to follow scale-dependent processes. 2 Here we study the scales of interactions and habitat selection in a long-ranging marine predator foraging from a central place, the yellow-nosed albatross. We use first-passage time analysis to identify the scales of interaction with environmental variables and compositional analysis to study habitat selection. 3 Of 26 birds, 22 adopted an area restricted search (ARS) at a scale of 130 ± 85 km, and 11 of these 22 birds adopted a second, nested ARS scale at 34 ± 20 km. Habitat use differed according to the spatial scale considered. At the oceanic basin macro-scale, birds foraged in pelagic, subtropical waters. Birds commuted to the ARS zones after a c. 1500-km trip to reach predictable turbulence zones from Agulhas return current, where primary productivity was enhanced at large scale. At a smaller, meso-scale, birds increased their search effort according to sea surface height anomalies (SSHa) and chlorophyll-a concentrations (Chl-a), indicating association with productive cyclonic eddies. 4 Among birds, differences in search pattern were noted: 11 birds concentrated their search effort directly at a small scale of 77 ± 22 km, avoiding anticyclonic eddies. The 11 other birds showed two scales of ARS pattern: (i) first at 180 ± 90 km with a preference for high Chl-a concentrations but unrelated to SSHa; and (ii) secondly at a nested scale at 34 ± 20 km related exclusively to SSHa where prey patches were expected to be distributed at this scale. This second group of birds appeared to be less efficient, spending more time at sea for the same mass gain than the first group. 5 Our study is the first to demonstrate scale-dependent adjustments, with interindividual variability, in relation to environmental features for predators with a central-place constraint.