Document Detail


Effects of intake rate on energy expenditure, somatic repair and reproduction of zebra finches.
MedLine Citation:
PMID:  16244168     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Understanding the effect of food availability on food requirements is critical when linking food availability e.g. to reproduction or habitat selection. Decreasing intake rate (intake per unit foraging effort) can be expected to increase daily energy expenditure (DEE), due to increased foraging costs. However, all the studies we could find that have tested this hypothesis (with one exception) found DEE to be constant or decreasing when intake rate was experimentally decreased. This may be due to the design of the reward schedule, which can be fixed (e.g. 20 units effort required for each reward) or variable (e.g. each unit effort rewarded with probability 1/20). Most studies used fixed reward rates, but foraging motivation is generally higher for variable reward rates, and the only study in which animals increased DEE when intake rate decreased used variable reward rates. To assess the generality of this result, we exposed zebra finches Taeniopygia guttata to different intake rates using variable reward rates. We decreased intake rate by mixing 25 g of seeds with 0, 25 or 75 g of chaff. With increasing chaff/seed ratio the time spent foraging increased from 6% to 27%, but this was insufficient to compensate for the lower intake rate, because DEE decreased by 6.6%. Body mass was independent of chaff/seed ratio. Effects of intake rate on foraging time and DEE were stronger at lower temperatures, when DEE was higher. The decrease in DEE in adverse conditions raises the question of what prevents such behaviour in benign circumstances. We hypothesize that energy is saved at the expense of ;condition', and we tested this hypothesis in two ways. Firstly, we tested the effect of intake rate on the replacement of two plucked tail feathers (a form of somatic repair). Replacement feathers were shorter when intake rate was low, indicating an effect of intake rate on somatic repair ability. Secondly, we tested for carry-over effects of intake rate on reproduction, by giving pairs the opportunity to reproduce with access ad libitum to food after feeding on one of the three chaff/seed ratios for 6 weeks. The interval until laying the first egg increased with decreasing intake rate in the preceding 6 weeks. The effects of intake rate on somatic maintenance and reproduction may explain why birds sustained higher metabolic rates than apparently necessary, but the physiological mechanisms determining the optimal metabolic rate remain to be discovered.
Authors:
Popko Wiersma; Simon Verhulst
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The Journal of experimental biology     Volume:  208     ISSN:  0022-0949     ISO Abbreviation:  J. Exp. Biol.     Publication Date:  2005 Nov 
Date Detail:
Created Date:  2005-10-24     Completed Date:  2006-06-12     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0243705     Medline TA:  J Exp Biol     Country:  England    
Other Details:
Languages:  eng     Pagination:  4091-8     Citation Subset:  IM    
Affiliation:
Zoological Laboratory, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands. wiersma.6@osu.edu
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MeSH Terms
Descriptor/Qualifier:
Animals
Body Constitution / physiology
Body Weight
Eating / physiology*
Energy Metabolism / physiology*
Feathers / growth & development*
Feeding Behavior / physiology
Finches / physiology*
Linear Models
Reproduction / physiology*
Temperature
Time Factors

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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