Foods of the black-bellied tree duck in South Texas

The foods of the Black-bellied Tree Duck in South Texas were, by volume, 92 per cent plant materials. Of these, sorghum and Bermudagrass predominated in both volume and percentage frequency. Other food plants included smartweeds, millets, water stargrass, and a single incidence of corn. Plant foods consisted only of seeds and did not include vegetative structures. Animal foods (8 per cent by volume) consisted of insects and mollusks. Each of these occurred about as often as the major plant foods. The snail, Physa anatina, seemed singularly important. Tree duck food habits change with the advance of the growing season. There is an initial period of "artificial" feeding on stockyard grains after the spring migration. This changes to Bermudagrass in May, then to sorghum in mid-summer. Daily stubble flights to sorghum fields continue into fall but the late summer diet is supplemented by water stargrass. Grit from tree duck stomachs averaged 1.4 grams per bird and showed considerable size variation.