The importance of food quantity and quality for reproductive performance in alpine water pipits (Anthus spinoletta) |
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Authors: | Paul A Brodmann H-U Reyer Kurt Bollmann Alex R Schläpfer Claudia Rauter |
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Institution: | Zoologisches Institut, Universit?t Zürich Winterthurerstrasse 190, 8057 Zürich, Switzerland fax: 0041-1-361 31 85; e-mail: ulireyer@zool.unizh.ch, CH
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Abstract: | Studies relating reproduction to food availability are usually restricted to food quantity, but ignore food quality and the
effects of habitat structure on obtaining the food. This is particularly true for insectivorous birds. In this study we relate
measures of reproductive success, time of reproduction and nestling size of water pipits (Anthus spinoletta) to biomass, taxonomic composition and nutritional content of available food, and to vegetation structure and distance to
feeding sites. Clutch size was positively correlated with the proportion of grass at the feeding sites, which facilitates
foraging. This suggests that water pipits adapt their clutch size to environmental conditions. Also, pipits started breeding
earlier and produced more fledglings when abundant food and a large proportion of grass were available, probably because these
conditions allow the birds to gain more energy in less time. The number of fledglings was positively correlated with the energy
content of available food. No significant relationships were found between feeding conditions and nestling size or the time
that nestlings took to fledge. This suggests that water pipits do not invest more in individual nestlings when food conditions
are favourable but rather start breeding earlier and produce more young. Taxonomic composition and nutritional content of
prey were not correlated with any of the reproductive parameters, indicating that profitability rather than quality of food
affects reproductive success.
Received: 31 May 1996/Accepted: 12 August 1996 |
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Keywords: | Foraging Habitat structure Nutrients Reproductive success Water pipits |
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