Document Detail

Skuas at penguin carcass: patch use and state-dependent leaving decisions in a top-predator.
MedLine Citation:
PMID:  16011919     Owner:  NLM     Status:  MEDLINE    
Foraging decisions depend not only on simple maximization of energy intake but also on parallel fitness-relevant activities that change the forager's 'state'. We characterized patch use and patch leaving rules of a top-predatory seabird, the Brown Skua (Catharacta antarctica lonnbergi), which during its reproductive period in the Antarctic establishes feeding territories in penguin colonies. In feeding trials, we observed how skuas foraged at penguin carcass patches and analysed patch leaving decisions by incorporating the estimated state of foraging birds and patch availability. Patches were exploited in a characteristic temporal pattern with exponentially decreasing remaining patch sizes (RPSs) and intake rates. Patch size decreased particularly fast in small compared to large patches and exploitation ended at a mean RPS of 47.6% irrespective of initial size. We failed to identify a measure which those birds equalized upon patch departure from raw data. However, when accounting for the birds' state, we ascertained remaining patch size and intake rates to have the lowest variance at departure whereas food amount and feeding time remained variable. Statistical correction for territory size only and combined with state had lower effects, but remaining patch size remained the measure with lowest coefficient of variation. Thus, we could clearly reject a fixed-time or fixed-amount strategy for territorial skuas and rather suggest a state-dependent strategy that equalizes remaining patch size. Thus our results provide evidence that under natural conditions, territorial skuas adjust their foraging decision on actual energy requirements, i.e. offspring number and age.
Steffen Hahn; Hans-Ulrich Peter; Silke Bauer
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Proceedings. Biological sciences / The Royal Society     Volume:  272     ISSN:  0962-8452     ISO Abbreviation:  Proc. Biol. Sci.     Publication Date:  2005 Jul 
Date Detail:
Created Date:  2005-07-13     Completed Date:  2005-10-04     Revised Date:  2010-09-20    
Medline Journal Info:
Nlm Unique ID:  101245157     Medline TA:  Proc Biol Sci     Country:  England    
Other Details:
Languages:  eng     Pagination:  1449-54     Citation Subset:  IM    
Institute of Ecology, Friedrich-Schiller University, Jena, Dornburger Strasse 159, 07743 Jena, Germany.
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MeSH Terms
Antarctic Regions
Charadriiformes / physiology*
Energy Intake / physiology*
Feeding Behavior / physiology*
Linear Models
Predatory Behavior / physiology
Spatial Behavior / physiology*

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