THE ROLE OF ENERGY-INTAKE RATE IN PREY AND HABITAT SELECTION OF COMMON EIDERS SOMATERIA-MOLLISSIMA IN WINTER - A RISK-SENSITIVE INTERPRETATION
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| Authors: | GUILLEMETTE, M; YDENBERG, RC; HIMMELMAN, JH |
| Year: | 1992 |
| Journal: | J. Anim. Ecol. 61: 599-610 Article Link (DOI) |
| Title: | THE ROLE OF ENERGY-INTAKE RATE IN PREY AND HABITAT SELECTION OF COMMON EIDERS SOMATERIA-MOLLISSIMA IN WINTER - A RISK-SENSITIVE INTERPRETATION |
| Abstract: | 1. We measured prey selection and habitat profitability of common eiders Somateria mollissima L. wintering in the Gulf of St. Lawrence, Quebec, Canada. Prey selection was evaluated by comparing the frequency of prey in stomachs of shot eiders with their frequency in the sublittoral zone. Habitat profitability was estimated using information on time spent feeding, foraging success, diving durations and energy content of the prey. 2. In this region, eiders forage on a variety of prey types from several distinct habitats, kelp beds, urchin barrens and beds of the phaeophyte Agarum cribrosum (Mert.). In kelp beds eiders feed mostly on small blue mussels Mytilus edulis L. Over barrens they capture green sea urchins Strongylocentrotus droebachiensis (Muller), and over Agarum beds they feed on both spider crabs Hyas araneus (L.) and urchins. 3. Flock size also varies with habitat type: all sizes of flocks feed in the kelp beds, whereas mostly small flocks feed in the barrens and Agarum beds. Small-flock individuals strongly select mussels and crabs whereas urchins are non-preferred prey. 4. Dive and foraging cycles differ significantly according to the above three habitats. Although, the size, density and energy content of prey differ markedly between kelp and Agarum beds, these two habitats offer an even energy return. However, the variance in energy return in these two habitats differs strikingly, being greater in the latter. We hypothesized, in the context of risk foraging theory, that this was related to flock sizes and body condition. As predicted, individuals feeding in small flocks were in bad condition compared to individuals feeding in large flocks. This suggests that small-flock individuals are seeking the habitat offering a variable intake to improve their survival probability. |
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