The importance of food quantity and quality for reproductive performance in alpine water pipits (Anthus sp. spinoletta)

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 sp. spinoletta) to biomass, taxonomic composition and nutritional contents of available food, and to vegetation structure and distance to feeding places. Clutch size was correlated positively with the proportion of grass at the feeding places, 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 correlated positively 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. Brodmann et al. 1 Feeding conditions and reproduction in water pipits Oecologia 109: 200-208 (1997) The importance of food quantity and quality for reproductive performance in alpine water pipits (Anthus sp. spinoletta) Paul. A. Brodmann, Heinz-Ulrich Reyer, Kurt Bollmann, Alex R. Schläpfer & Claudia Rauter Zoologisches Institut, Universität Zürich Winterthurerstrasse 190, 8057 Zürich, Switzerland Correspondence author: Heinz-Ulrich Reyer Zoologisches Institut Universität Zürich Winterthurerstrasse 190 CH-8057 Zürich, Switzerland Tel.: 0041-1-257 49 80 FAX: 0041-1-361 31 85 e-mail: [email protected]