Time budget, habitat use and breeding success of White Storks Ciconia ciconia under variable foraging conditions during the breeding season in Switzerland

Following its extinction in 1950, the White Stork Ciconia ciconia was reint roduced to Switzerland. We analysed time budget, habitat use and breeding s uccess of 28 breeding pairs at five sites in 1994. At two sites the adults were given extra food daily (SF), at the others no supplementary food was p rovided (NSF). During the first 20 days of life of the young, at least one adult stayed at the nest almost all the time. Later, adults left their youn g unguarded for increasing periods, NSF for longer periods than SE Feeding rates of the young were higher in SF than in NSF. Outside the nest, SF spen t more time foraging and less time flying than NSF. Foraging distances were larger in NSF than in SF. Overall breeding success was generally low in Sw itzerland in 1994 (1.2 versus 1.7 young per breeding pair 1965-98), mainly due to bad weather, and it did not differ significantly between NSF and SF. Furthermore, size and weight of the young did not differ between NSF and S F. Breeding success did not differ significantly between NSF and SF sites i n years with an high overall reproductive output (1992, 1993). We conclude that surplus food did not enhance breeding output. It is yet unclear whethe r a long term breeding success of 1.7 young per breeding pair (1965-98) is sufficient to maintain a stable population.