[43] There is also a significant population of female floaters; a 1985 study estimated that around 23% to 27% of females were floaters, of which about 47% to 79% were subadults. The nest hole in these situations is, on average, 3.4 metres (11 ft) above ground level, although about 45% of them are less than 2 metres (6.6 ft) above the ground. It is likely involved in pair bonding. This can benefit the male, but since the female controls copulation, the lack of resolution on how this behaviour benefits females makes the high level of extra-pair paternity puzzling. Juveniles have brown upperparts, and a grey-brown-washed breast. The American tree sparrow is 5-6 inches in length with a wingspan of 8-9 inches. One theory, called the genetic compatibility hypothesis, states that increased offspring fitness results from increased heterozygosity, and thus that female tree swallows would prefer to mate with males that are less genetically similar to them. The nestlings, like the adult, primarily eat insects, fed to it by both sexes. [38] It is suggested that this polygyny depends on the conditions during the laying season: better conditions, such as an abundance of food, allow females in polygyny who do not receive help foraging to lay more eggs. [72], The tree swallow is susceptible to a wide range of predators. A 2001 study found that out of 35 extra-pair nestlings, 25 were sired by local residents, three by residents of nearby sites, and seven by male floaters. [7] The nest cup itself is made from grass, moss, pine needles, and aquatic plants collected mostly by the female,[14] and is lined with feathers gathered primarily by the male in fights. An aerial insectivore, the tree swallow forages both alone and in groups, eating mostly insects, in addition to molluscs, spiders, and fruit. When the male arrives during incubation, it sometimes commits infanticide, but other times adopts the eggs, as there is a chance that some eggs were sired from the replacement male. Geographic Range. "Studies of a tree swallow colony". During the breeding season, this is mostly within 4 kilometres (2.5 mi) of the nest site. The breast of the American Tree Sparrow is buff-colored contrasting with the gray breast of a Chipping Sparrow. But, the age of a female does not affect both the acquired and innate humoral immunity; the lack of deterioration in the former contrasts with studies on barn swallows and female collared flycatchers. [79], In the breeding female tree swallow, humoral immunocompetence (HIC) is inversely correlated with laying date. A later hatching date negatively impacts growth, especially for younger nestlings. Most American tree sparrows live two to three years in the wild. He aggressively protects his territory. [85], The tree swallow is considered to be least concern by the International Union for Conservation of Nature. Second-year refers to the second year of life; therefore, a "second-year female" is one year old. Incubation takes about 12 days. This U.S.-Canada Stewardship species rates a 9 out of 20 on the Continental Concern Score and are not on the 2014 State of the Birds Watch List. There is no overlap between its breeding grounds and its winter territory. Otherwise, the diet is about 90% flies. The female incubates the eggs. Older chicks grow somewhat faster when insects are abundant. When it is foraging for nestlings, though, it usually goes up to 200 metres (660 ft) from the nest,[14] mostly staying in sight of it, and forages at a height up to 12 metres (39 ft). Females may also choose sperm after copulation to ensure a compatible mate. [14] The wintering range is from California and southwestern Arizona in the west and southeastern Virginia in the east south along the Gulf Coast to the West Indies, Panama, and the northwestern South American coast. Drastic decline. [7], The generally accepted genus name is from Ancient Greek takhykinetos, "moving quickly", and the specific bicolor is Latin and means "two-coloured". Wingspan ranges from 11.8-13.8 in (30-35 cm). A 2014 study, for example, found that broods for whom white noise was played were less likely to crouch or stop begging in response to alarm calls.

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