The tree swallow breeds in North America. The mangrove swallow is very territorial when breeding, much like the related tree swallow. The tree swallow breeds in the US and Canada. In the tree swallow, some components of the immune system deteriorate with age. During courtship, a male tree swallow attacks an unknown female. The tree swallow is susceptible to a wide range of predators. In natural cavities, the tree swallow nests about apart from its neighbor. The tree swallow has a length between about and a weight of approximately . The tree swallow forages up to above the ground singly or in groups. The large tree swallow ("Tachycineta bicolor") flocks here. Acquired T cell-mediated immunity, for example, declines with age in the female tree swallow. In the breeding female tree swallow, humoral immunocompetence (HIC) is inversely correlated with laying date. A tree swallow that is handicapped by wing-clipping generally has a lower HIC. The tree swallow eats mostly insects, with some molluscs, spiders, and fruit. The tree swallow is also called the white-bellied swallow for its white underparts.