Both sexes feed the nestlings (although the male feeds the chicks less than the females) resulting in about 10 to 20 feedings per hour. The parents often use the chirp call to stimulate nestlings to beg. This is used more frequently with younger chicks, as they beg less than older chicks when the parent arrives with food but does not call. The likelihood of begging in the absence of parents also increases with age. The hatching order affects how much a chick is fed; last-hatched nestlings (in cases where hatching is asynchronous) are likely fed less than those hatched earlier. Nestlings closer to the entrance of the nest are also more likely to be fed, as are those who beg first and more frequently. The overall rate at which a brood is fed also increases with more begging. The diet itself is composed mostly of insects, those in the orders Diptera, Hemiptera, and Odonata making up most of the diet. These insects are mostly up to in size, but sometimes are up to in length. In nests near lakes acidified by humans, calcium supplements, primarily fish bones, crayfish exoskeletons, clam shells, and the shells of bird eggs, are harder to find. This forces the adult tree swallow to travel further than usual—sometimes up to away from the nest—to get these calcium supplements.