Foraging effort of Surf Scoters (Melanitta perspicillata) wintering in a spatially and temporally variable prey landscape

Abstract

We monitored foraging effort of radio-tagged Surf Scoters (Melanitta perspicillata (L., 1758)) in three different habitats: (1) shellfish farm structures with high densities of mussels and strong seasonal prey depletion, (2) soft-bottom clam beds with more stable but less available prey, and (3) rocky intertidal beds with moderate mussel densities and depletion rates. We predicted that foraging effort would vary uniquely by habitat, with effort increasing more where depletion was strongest. However, variation in both hourly and daily foraging efforts was best explained by date only. Effort per hour was lowest in early December (presumably owing to very high prey abundance), increased until mid-February as prey declined, and then decreased again in March (probably owing to increased daylight time for foraging). Foraging effort estimated over a full day increased steadily from December to March as prey were depleted. Temporal patterns of effort did not vary by habitat after accounting for seasonal effects. Instead of increasing foraging effort in habitats with strong depletion, Surf Scoters redistributed to habitats with lower degrees of prey reduction as the season progressed. We suggest that Surf Scoters respond to variation in prey by adjusting both foraging effort and habitat selection as the prey landscape changes.

Using an algorithmic model to reveal individually variable movement decisions in a wintering sea duck

“…However, we could not include potential depletion of food resources during the course of the winter in our model. Common eiders (Somateria mollissima, L.) have been shown to deplete mussel beds (Guillemette et al 1996), and prey depletion in mussel farms induced foraging surf scoters (Melanitta perspicillata, L.) to move to different habitats in late winter (Kirk, Esler & Boyd 2007). King eiders generally forage in deeper water than surf scoters and common eiders (Bustnes & Erikstad 1988) where prey depletion may be less likely (Larsen & Guillemette 2000).…”

Spring migration routes and chronology of surf scoters (Melanitta perspicillata): a synthesis of Pacific coast studies

“…Depletion of spawn or alternate benthic and epibenthic prey (Kirk et al 2007;Anderson et al 2008) could be one factor spurring inland migration. Prey availability in high-latitude freshwater lakes may be less predictable than in coastal waters because of their ephemeral nature (Piersma 2003).…”

Variation in body mass and foraging effort of Barrow’s Goldeneyes (Bucephala islandica) during remigial molt

“…They also foraged at rates similar to those observed for goldeneyes during fall staging (D. Hogan unpubl. data), and rates similar to, or less than, those of other ducks at other stages of the annual cycle (Custer et al 1996, Fischer and Griffin 2000, Systad and Bustnes 2001, Kirk et al 2007, Lewis et al 2007, Schummer et al 2012). However, Leddy Lake birds foraged primarily at night, whereas Cardinal Lake birds foraged primarily diurnally, which once again suggests environmental influences on energy management strategies.…”