Title
Pushed for time or saving on fuel: fine-scale energy budgets shed light on currencies in a diving bird
Author(s)
Shepard, E.L.C.; Wilson, R.P.; Quintana, F.; Laich, A.G.; Forman, D.W.
Published
2009
Publisher
Proceedings of the Royal Society B: Biological Sciences
Abstract
Animals may forage using different currencies depending on whether time minimization or energy maximization is more pertinent at the time. Assessment of net energy acquisition requires detailed information on instantaneous activity-specific power use, which varies according to animal performance, being influenced, for example, by speed and prey loading, and which has not been measured before in wild animals. We used a new proxy for instantaneous energy expenditure (overall dynamic body acceleration), to quantify foraging effort in a model species, the imperial shag Phalacrocorax atriceps, during diving. Power costs varied nonlinearly with depth exploited owing to depth-related buoyancy. Consequently, solutions for maximizing the gross rate of gain and energetic efficiency differed for dives to any given depth. Dive effort in free-ranging imperial shags measured during the breeding season was consistent with a strategy to maximize the gross rate of energy gain. We suggest that the divergence of time and energy costs with dive depth has implications for the measurement of dive efficiency across diverse diving taxa.
Keywords
METABOLIC-RATE; ANIMALS; ACCELERATION; EXPENDITURE; BEHAVIOR; DEPTH; AIR; STRATEGIES; ALLOCATION; CORMORANT; Central place foraging;Currency;Energy expenditure;Foraging strategy;Time-energy budget

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PUB10369