ANIMAL ESTATE client 3.2: TREE SWALLOW
FROM ANIMAL ESTATES 3.0: CAMBRIDGE
SCIENTIFIC NAME: Tachycineta bicolor
ANIMAL PROFILE: The Tree Swallow is a beautiful little bird from the Swallow family. It averages 13.5 cm (5 inches) long and weighs about 20g. The bill is tiny. The adult Tree Swallow has iridescent blue-green upperparts, white underparts, and a very slightly forked tail. The female usually has duller colors than the male, often more greenish than the more bluish male.
Tree Swallows are aerial feeders. They forage over land and water, swerving and dipping to feed on flying insects such as beetles, midges, crane flies, horseflies, ants, moths, grasshoppers, dragonflies, and mayflies. In winter, they sometimes feed on berries, especially those of the wax myrtle. Tree Swallows and Myrtle Warblers are the only birds that can digest these berries, and this might help explain why Tree Swallows winter farther north than any other North American swallow. Tree Swallows forage mainly near their nest sites, either alone or in loose flocks.
Although Tree Swallows are generally monogamous, some males may have more than one mate simultaneously. Pair bonds last for the duration of the breeding season. Often, the same pairs will mate in consecutive breeding seasons. This appears to be the result of both sexes returning to the same nest site year after year, rather than the result of a long-term pair bond.
In some populations, eggs are laid beginning in late April; in others, egg-laying begins in late May. Throughout most of the Northeast, the bulk of egg laying usually takes place in mid-May.
Females can lay between 4-6 eggs, only laying one egg per day, but there are occasionally large gaps between the laying of consecutive eggs. Eggs are laid in the morning, usually within two hours of sunrise. The eggs are pure white and become slightly glossy after a few days of incubation.
The incubation period is 14 to 15 days. Females incubate the eggs, but males will guard the nests when females are absent. The young are fed soon after they hatch, and both parents share this duty equally. In situations where one adult has disappeared, a single parent can raise the young alone. Nevertheless, retarded nestling growth, brood reduction, and starvation are typical outcomes. Fecal sacs are removed from the nest until the young are 14 days old. Nestlings fledge after 16 to 30 days, and many are virtually independent immediately upon their departure.
RANGE: Tree Swallows are found all across the continental United States and Canada, and in parts of Alaska, as far north as cavities are available, avoiding only the southeastern corner of the U.S. In fall and winter, Tree Swallows form migratory flocks that can contain anywhere from a few thousand to a million individuals. They head to the southern coast of the United States, Mexico, and Central America. In early spring, a small percentage of the young return to their birthplaces. They do not breed on the natal territory itself but rather settle some distance away. This distance varies, depending on the population.
HABITAT: Tree Swallows prefer open habitats, such as the edges of woods, and areas near water, including marshes, shorelines, and swamps, which can be breeding grounds for insects. Also, Tree Swallows are quite tolerant of humans.
COMMUNITY: Outside of the breeding season, Tree Swallows are highly social birds. They gather in enormous flocks along the coast in fall, where they circle in big eddies like leaves caught in a whirlwind. During the breeding season, however, these swallows are territorial and aggressively defend their nests against other Tree Swallows (called conspecifics) and against other species. They are solitary nesters, but they may nest in loose aggregations with nests 10 to 15 meters from one another. They frequently compete for nest sites with House Wrens and House Sparrows.
HOME CONSTRUCTION: Nesting is quite synchronous in Tree Swallows; that is, females tend to begin nesting within a week or 10 days of their neighbors. Tree Swallows are hole dwellers/ cavity dwellers and nest in natural tree cavities, woodpecker holes, and nest boxes. They have greatly benefited from the proliferation of bluebird boxes, as they will readily use boxes of that size and configuration. The female builds the nest. This process is governed by the weather. In typical springs, the nest can take up to three weeks to complete, but if conditions are very good and the birds are late, the nest can be completed in a few days. Nests are typically 1 to 10 meters off the ground. The same nest sites are used for more than one breeding season, and pairs will often nest on top of old nests.
BUILDING MATERIALS: The Tree Swallow’s nest is an open cup of grass or pine needles placed in tree cavity or nest box. They also use many feathers from other birds in their nests. The feathers help keep the nestlings warm so they can grow faster. They help keep levels of ectoparasites, like mites, low too.
THREATS: Hole-nesters such as the Tree Swallow often face a housing shortage and must fight to get into, or keep, woodpecker holes or other sought-after nest sites. Man-made breeding boxes may help increase the numbers of these birds.
INTERESTING FACTS:
• Outside of the breeding season the Tree Swallow congregates into enormous flocks and night roosts, sometimes numbering in the hundreds of thousands. They gather about an hour before sunset at a roost site, forming a dense cloud. They swirl around like a living tornado and as darkness approaches they then wheel low over the cattail marsh or grove of small trees. Large numbers drop down into the roost with each pass of the flock until the flock disappears.
• For reasons which are still under investigation, Tree Swallows are known to enjoy playing with a feather, which they drop and then retrieve as it floats in the air.
MAKING A TREE SWALLOW NESTING BOX: Below are three sites with instructions on building Tree Swallow Nesting Boxes. Once you have completed the construction, mount your box on a tree trunk or post, or hang from a tree branch or under an eave between four and twenty feet high with partial sun and shade. Place several boxes in a yard or field edge; they welcome neighbors. They also make great neighbors for bluebirds and help chase sparrows away.
Webites with Plans:
http://www.50birds.com/MPb050806112.htm
http://www.shawcreekbirdsupply.com/plans_tree_swallow.htm
http://www.sialis.org/kinney.htm
Websites with tips for building Tree Swallow Nesting Boxes:
http://www.dccl.org/information/houses/birdhouses.htm
http://www.sialis.org/tresdead.htm
http://www.treeswallowprojects.com
REFERENCE SITES:
USGS website
The Birdhouse Network from the Cornell Lab of Ornothology:
Wikipedia
eNature: