Nestling tree swallow (Tachycineta bicolor) diets in an upland old field in western Michigan

We collected and identified 1852 prey items from 89 boluses delivered to 61 nestling tree swallows (Tachycineta bicolor) at 14 nests in an upland old field in western Michigan. We found that 90.8% of nestling diets was insect s from the Orders Diptera, Homoptera, Hymenoptera and Coleoptera. We also f ound clam and snail shells in boluses. Over the most common brood sizes of 4-6 nestlings, brood size was inversely proportional to the number of items per bolus delivered to nestlings although mean dry and mean organic weight of boluses did not differ. Bolus composition was not influenced by weather conditions. Nestling diets at our study site were similar in the proportio ns of many prey items, such as Diptera and Homoptera, to tree swallow nestl ing diets in other habitats but contained fewer aquatic forms such as Odona ta and Ephemeroptera.