The growth and survival of nestling tree swallows is influenced by their environment. In both younger and older nestlings (those between two and four days old and between nine and eleven days, respectively) growth is positively influenced by a higher maximum temperature, particularly in the former. A later hatching date negatively impacts growth, especially for younger nestlings. Older chicks grow somewhat faster when insects are abundant. Growth in younger nestlings increases with age, while in old nestlings, it decreases as they get older. Young tree swallows are able to thermoregulate at least 75% as effectively as the adult at an average age of 9.5 days when out of the nest, and from four to eight days old when in the nest (depending on the size of the brood). The nestlings fledge after about 18 to 22 days, with about 80% fledging success. Like hatching success, this is negatively affected by unfavourable weather and a younger female. Chicks may be preyed on by snakes and raccoons. This predation can be exacerbated by begging calls.