The number of visits to the nest by parents is an accurate measure of food delivered to nestlings in Tree Swallows

The number of visits parents make to their nest during chick rearing is a commonly used measure of the amount of food delivered to nestlings and an index of the quality of parental care. Use of the number of visits for these purposes assumes that parents feed nestlings when they visit and that there are no systematic differences in the amount of food delivered on each visit. These assumptions were tested in Tree Swallows (Tachycineta bicolor) breeding in nest boxes near Ithaca, New York. Video observations of parents inside their nest boxes showed that parents feed nestlings on 95-98% of visits to the nest. An average visit delivered 18.1 insects with a total dry mass of 24.1 mg, usually to a single nestling. Although females visited more frequently, the load they carried on each visit was not different than that carried by males. Load size did not differ with nestling age, brood size or the date of the feeding. Overall, there were few systematic differences in load size among nests. Therefore, the number of visits to the nest is a good measure of food delivery and parental care in Tree Swallows.