Foraging and provisioning in Antarctic fur seals: interannual variability in time-energy budgets |
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Authors: | Boyd I L |
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Institution: | British Antarctic Survey, NERC, Madingley Road, Cambridge CB3
OET, UK |
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Abstract: | This study examined three competing hypotheses to explain howlactating
Antarctic fur seals (Arctocephalus gazella) respondto changes in the
level of resource availability. Antarcticfur seals have episodic bouts of
suckling (1-3 days), alternatingwith foraging trips (3-10 days). Foraging
time budgets variedsignificantly (p <.001) among 8 consecutive
years at BirdIsland, South Georgia. Foraging trip duration increased during
periodsof relative food shortage. Time spent ashore was more consistentamong
years than foraging trip duration but declined duringa year of particularly
low food availability. In 4 of the 8years, there was a significant positive
correlation betweentime spent ashore and foraging trip duration. In the other
years,the relationship was close to statistical significance. Energydelivery
to pups during suckling bouts followed an asymptoticpower function. Energy
gain during foraging trips was estimatedfrom diving behavior, which suggested
that the energy gain functionwas linear. Distance traveled during foraging
trips was correlatedwith foraging trip duration, and long foraging trips were
associatedwith reduced foraging intensity. There was support for the
hypothesisthat lactating Antarctic fur seals compensate for reduced resources
byincreasing the foraging trip duration rather than working harderand
increasing their energy expenditure. However, there wasmost support for the
hypothesis that lactating Antarctic furseals adjust time spent ashore as well
as foraging trip duration,possibly to maximize the delivery of food to their
offspring.Lactation appears to impose constraints on provisioning of
offspringthat differ from those of seabirds foraging in the same environment
andoften on the same prey. |
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Keywords: | Arctocephalus gazella Antarctic fur seals lactation optimization provisioning time budgets |
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