Diet of young Great Bustards Otis tarda in Spain: sexual and seasonal differences

Abstract

Capsule Arthropods are the most important diet component of Great Bustards Otis tarda in the first months of life.Aims To determine the diet composition of young Great Bustards in Spain.Methods The diet was estimated by stomach content analysis (n = 49).Results Stomach contents' dry weight consisted of 33% arthropods, 30% green plant material and 23% seeds. Gastroliths were only found in summer and autumn. The diet composition changed significantly between seasons. In summer, diet consisted mainly of arthropods (50%), with green plant material being the main component in winter (56%). Volume of stomach contents and mean size of ingested arthropods were higher in males than in females. Diet composition did not differ between sexes. In summer, ground-dwelling and plant-visiting arthropods such as Mantidae, Tenebrionidae and caterpillars were the most abundant. In winter, weeds, legumes and cultivated seeds were more frequent than arthropods. Cereal plants were the least consumed in all seasons, although Barley and Wheat seeds played an important role during winter and autumn.Conclusion The results highlight the importance of arthropods and weeds as a fundamental component of the diet of young Great Bustards. Because previous studies show that arthropods and weeds are usually more abundant in extensive farming, we recommend the implementation of agri-environmental measures in Great Bustard breeding areas.