nomes no trilho de navegação
Violet-green swallows often rest on exposed perches such as tree branches and telephone wires. They fly at various heights and can be seen swooping down to skim the surface of ponds and lakes, flying at greater heights and beating their wings more rapidly than other swallows. While the species is extremely social and nests in colonies of up to 25 pairs, with some colonies having over twenty couples in a single tree, they are also capable of nesting solitarily. In addition, they are very social with members of other species of swallows and will often forage in interspecies groups of from 3 to over 50 individuals.
The IUCN Red List currently places T. thalassina in the category of “Least Concern.” This classification is due largely to the violet-green’s extensive range and to its ability to nest in both remote and urban locations, which creates a lessened impact from human development. While there is little research on the benefits of human efforts to assist with nesting, it has been observed that nest boxes have been helping these birds in different regions of their range. The National Audubon Society, however, states that violet-green swallows are “Climate Threatened” and provides maps and projections of how climate change might affect this species.
For nesting habitats, violet-green swallows occupy open or broken deciduous, coniferous, and mixed woodlands, mainly preferring trees in open areas, as well as cliffs, buildings, and other manmade structures. They sustain themselves on a diet of insects, primarily tree dwelling flying insects. Peregrine falcons and merlins are two of their biggest predatory threats. There is a significant danger of habitat destruction confronting these birds, but their numbers are fairly abundant and their habitat range is fairly large. There is some evidence of this species interacting with Western bluebirds in a commensalist manner, assisting with the rearing of young bluebirds and then using the bluebird nest as their own.
The habitat of the violet-green swallow is widespread when foraging. While breeding, they will roost in open deciduous, coniferous, and mixed woodlands, including ponderosa pine, Monterey pine, and quaking aspen. In the southern part of the range, they live most commonly at elevations of 2,000 to 3,500 feet, although they also nest in wooded canyons. Farther north, they breed and nest at lower elevations. When nesting, violet-green swallows can be found in open woodlands, mountains, and urban settings. While migrating, they will roost in semi-open areas, such as forests, canyon walls, or on the ground if no elevated spots are available.
Violet-green swallows typically will produce one brood per mating season, although second broods occasionally occur. The eggs have an incubation period of 13-15 days and the fairly helpless hatchlings have pale pink skin with wisps of creamy or grayish down on their backs, eyes yet to be opened, and a distinct creamy-whitish gape. At day 5, their skin darkens and their feather follicles begin to appear. At day 7, vocalizations begin to occur as they make their first ‘peep’. Between days 8-9, their eyes begin to open, their feather remiges begin to break through the sheaths, and finally the young begin to defecate in specific nest spots. At day 10, the nestlings are finally making double note noises and white feathers are appearing along the sides of their bodies. By day 16, the young have stopped gaping their mouths, their primary feathers are one inch long, their sides are covered with white silky feathers and their backs are covered in black fur. By day 18, the bird looks like an adult, with the only distinction being their protruding abdomen, which will begin to reduce in a few days. By day 22, the bird has full-length wing and tail feathers and is almost being completely mature. It will most likely fledge by day 24 or 25 and will lose its dependency on adults by day 27 or 28. Although there is limited information on the lifespan of violet-green swallows, the oldest known male was recorded to be over 9 years old.
The violet-green swallow (Tachycineta thalassina) is a small songbird in the Hirundinidae family. They are about 12 cm in length, with a wingspan of 27 cm and a weight of 14 g (All About Birds 2016). They are an iridescent violet-green on the crown, nape, and back, white on the underside, with white also on the sides of their heads. T. thalassina is native to Western North America, ranging from Alaska to Mexico, and is usually found in open woodlands, mountains, and various urban settings, where they can be observed flocking with others of their kind or with a variety of swallow species (Seattle Audubon 2016). The swallows feed mainly on flying insects, including flies, bees, true bugs, and beetles, which are caught in flight at different heights. They feed both independently and in small flocks, flying low over fields or water or circling and swooping from significant heights, often foraging at higher altitudes than other swallows (Brown, Knott, and Damrose 2011). They begin nesting in the spring, building their nests with twigs, grass, straw, and feathers. Eggs will be laid one per day until the clutch of 4-6 white eggs is finished, and females will then incubate the eggs for 14 to 15 days. After the eggs hatch, the adult female and male birds will both take part in feeding the young, and will continue to feed them for a short time after the young leave the nest, which occurs 23-24 days after hatching (Seattle Audubon 2016).
Like most other swallows, the violet-green swallow is an insectivore, which makes them heterotrophic and secondary consumers. Since they hunt primarily in flight, their diet is made up of flying insects such as bees and flies, although they have been known to consume ants and spiders as well. As with most other birds of similar size, the violet green swallow has few predators; only small birds of prey such as falcons and merlins are able to catch these agile flyers. Since these predators are relatively few in number, violet-green swallows occupy a comfortable niche in their food web, feeding on plentiful insects without fear of terrestrial predators. Even house cats pose little threat to violet-greens because they rarely stop to land and when they do it is generally in trees, on rooftops, or on telephone wires and almost never on the ground.
