Balancing energy budget in a central-place forager: which habitat to select in a heterogeneous environment?

PLoS One. 2014 Jul 16;9(7):e102162. doi: 10.1371/journal.pone.0102162. eCollection 2014.

Abstract

Foraging animals are influenced by the distribution of food resources and predation risk that both vary in space and time. These constraints likely shape trade-offs involving time, energy, nutrition, and predator avoidance leading to a sequence of locations visited by individuals. According to the marginal-value theorem (MVT), a central-place forager must either increase load size or energy content when foraging farther from their central place. Although such a decision rule has the potential to shape movement and habitat selection patterns, few studies have addressed the mechanisms underlying habitat use at the landscape scale. Our objective was therefore to determine how Ring-billed gulls (Larus delawarensis) select their foraging habitats while nesting in a colony located in a heterogeneous landscape. Based on locations obtained by fine-scale GPS tracking, we used resource selection functions (RSFs) and residence time analyses to identify habitats selected by gulls for foraging during the incubation and brood rearing periods. We then combined this information to gull survey data, feeding rates, stomach contents, and calorimetric analyses to assess potential trade-offs. Throughout the breeding season, gulls selected landfills and transhipment sites that provided higher mean energy intake than agricultural lands or riparian habitats. They used landfills located farther from the colony where no deterrence program had been implemented but avoided those located closer where deterrence measures took place. On the other hand, gulls selected intensively cultured lands located relatively close to the colony during incubation. The number of gulls was then greater in fields covered by bare soil and peaked during soil preparation and seed sowing, which greatly increase food availability. Breeding Ring-billed gulls thus select habitats according to both their foraging profitability and distance from their nest while accounting for predation risk. This supports the predictions of the MVT for central-place foraging over large spatial scales.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Charadriiformes / metabolism*
  • Diet
  • Ecosystem*
  • Energy Metabolism*
  • Feeding Behavior*
  • Nesting Behavior
  • Predatory Behavior

Grants and funding

The research was supported by grants to JFG and MB from the Natural Sciences and Engineering Research Council of Canada, the Canadian Wildlife Service, ICI Environnement, Falcon Environmental Services, Chamard et Associés, Waste Management, and BFI Canada. MPM was supported by a scholarship from the Natural Sciences and Engineering Research Council of Canada. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.