Most do not go far, usually breeding at sites less than 10 kilometres (6.2 mi) away from their original grounds.  After finding a suitable place to nest, the male perches near it and calls frequently.  The likelihood of begging in the absence of parents also increases with age. The whine, generally consisting of a downward shift in frequency followed by an upward shift, may be given alone as the anxiety call, occasionally made in response to certain predators.  The juvenile tree swallow can be distinguished by its brown upperparts and grey-brown-washed breast. Regardless, a 2016 thesis found that measures of condition were positively correlated with telomere length. Part I. Owls". Eggs. Another theory suggests that extra-pair paternity is context dependent, with extra-pair young outperforming within-pair young in certain situations, and underperforming in other environments. Iridoprocne bicolor Coues, 1878.  Nestlings also suffer from parasites, like blow-flies of the genus Protocalliphora, which results in a loss of blood by nestlings. This means that, on average, a bird that lays its eggs earlier has a stronger antibiotic response to an antigen than a bird that lays later. They are also likely to lose weight because of an infection. The tree sparrow decline started in the 1970s, and even with recent increases, the … The American tree sparrow breeds in the tundra.  Nestlings closer to the entrance of the nest are also more likely to be fed, as are those who beg first and more frequently.  Most deaths are likely the result of cold weather, which reduces insect availability, leading to starvation. (1955).  The gurgle, as when it appears at the end of the song, is usually uttered twice. Although it is aggressive during the breeding season, this swallow is sociable outside of it, forming flocks sometimes numbering thousands of birds. "Tree Swallow (. They generally fledge about 18 to 22 days after hatching.  It seems to alter the intensity of its attacks based on which predator approaches; a 1992 study found that ferrets elicited a more vigorous defence than black rat snakes, and a 2019 thesis similarly discovered that black rat snake models were dived at the least and eastern chipmunk models the most. , In the tree swallow, some components of the immune system deteriorate with age.  The diet itself is composed mostly of insects, those in the orders Diptera, Hemiptera, and Odonata making up most of the diet. The female incubates the clutch of two to eight (but usually four to seven) pure white eggs for around 14 to 15 days.  It nests both in loose groups and isolated pairs. In the non-breeding season its is found in a variety of habitats including open woodlands, marshes, deserts, fields, gardens, and farmland. Copulation occurs multiple times. "Studies of a tree swallow colony".  Whether short telomeres cause a reduction in fitness or are simply an indicator of it is unknown.  The insects taken are a mix of aquatic and terrestrial organisms; the former is an important source of omega-3 highly unsaturated fatty acids. In support of this theory, a 2007 study found that extra-pair offspring were more heterozygous than within-pair offspring. Juveniles have brown upperparts, and a grey-brown-washed breast.  It is suggested that the snake prompted a weaker response because defence behaviours may be less effective and more dangerous to perform against it. , The tree swallow eats mostly insects, with some molluscs, spiders, and fruit. , The tree swallow has a length between about 12 and 14 cm (4.7 and 5.5 in) and a weight of approximately 17 to 25.5 g (0.60 to 0.90 oz). This can result in a weight hierarchy where earlier-hatched chicks weigh more (especially early in the nestling period) than those hatched later, allowing the female to prioritize which chick to give food to during food shortages.  The male has mostly glossy blue-green upperparts, the wings and tail being blackish. The tree swallow is sometimes considered a model organism, due to the large amount of research done on it. During the breeding season, this is mostly within 4 kilometres (2.5 mi) of the nest site. The American tree sparrow eats seeds, berries, and insects. About 88% of nests produce at least one nestling, but this can be lowered by poor weather and a younger breeding female. This relationship is speculated to be a cause of an improved microclimate for fleas due to a larger clutch. Parents did not alter their calls to compensate, likely increasing predation risk. The female incubates the eggs. A lack of sites can cause fights between birds, sometimes resulting in deaths. , The tree swallow is susceptible to a wide range of predators. 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. The female is generally duller than the male, and the first-year female has mostly brown upperparts, with some blue feathers. Found in the Americas, the tree swallow was first described in 1807 by French ornithologist Louis Vieillot as Hirundo bicolor. Acquired T cell-mediated immunity, for example, declines with age in the female tree swallow. Geographic Range.  The second-year[note 1] female also has brown upperparts, with a variable number of blue feathers; some third-year females also retain a portion of this subadult plumage.