HABITAT SELECTION BY FORAGING WHITE STORKS, CICONIA-CICONIA, DURING THE BREEDING-SEASON

Foraging habitat selection by breeding White Storks (Ciconia ciconia) was studied at two contrasting areas in Spain, in relation to physical features of the terrain, food availability, and distance to the colony. In the first area, where storks captured mainly orthopterans, they selected tall-grass pastures and recently ploughed cereal fields, which were the habitats with highest densities and largest average sizes of prey. In the second area, where storks preyed almost exclusively on earthworms, flooded and open ash groves with short grass and high densities of earthworms were the preferred habitat. In this area, marked storks dispersing farther to feed in selected open ash groves more often than in dense ones. Foraging bouts, were longer, aggregations were larger, and food intake rates were greater, in open ash groves than in dense ones, owing to greater earthworm availability and accessibility. Depletion of earthworms led to an increased distance of dispersal to forage in the second area, but not in the first, where because of rapid reproduction of orthopterans, the birds were not forced to forage at greater distances later in the season.