Then there were the tree swallows, which had not been known to breed in the park since 1868.

"They stayed for about a week, but then got chased out by some tree swallows," he said.

Thousands of tree swallows forage on the refuge in the late summer.

We paused to catch our breath and watch what must have been a million tree swallows pass by on their way from summer to winter.

The tree swallows lined up on television aerials looked like clothespins.

The trail has 40 birdhouses to attract tree swallows and bluebirds.

Tree Swallows are typically single-brooded, although they may attempt a second nest if the first fails early in the season.

It is designed for bluebirds, tree swallows, nuthatches and house wrens.

Nest boxes are meant to attract bluebirds, tree swallows and house wrens.

Tree Swallows are known to "fight" over feathers in mid-air for reasons which are still under investigation.

Phoebes take bugs on the wing, and so do the few tree swallows who live around here, and of course the bats.

An earlier study of tree swallows had the opposite result, showing that individual begging intensity increases with number of offspring.

The river's tree swallows are also showing signs of reproductive problems, a side effect of the chemicals documented in laboratory animals.

Being highly social outside of the breeding season, tree swallows may form flocks of several thousand birds near roost sites.

Ducks and grebes have set down for a short stay and tree swallows have moved into nesting boxes.

(Tree swallows are also fond of mosquitoes.)

Like the related Tree Swallow, this species is very aggressive to other hirundines when breeding, and nests are several hundred metres apart.

Research projects focused on red winged blackbirds, cow birds, tree swallows, plant succession, insect-goldenrod interaction, and bats.

The large Tree Swallow (Tachycineta bicolor) flocks here.

Nesting species include Swainson's hawks, great-horned owls, wood ducks, tree swallows, and black phoebe.

The adult Tree Swallow has iridescent blue-green upperparts, white underparts, and a very slightly forked tail.

Two pairs of tree swallows were nesting in trees less than 50 feet apart on the island, and a pair of robins was setting up housekeeping.

"And Skimmer the Tree Swallow," added Jenny.

Declines in cavity-builder populations are resulting in fewer natural nesting sites for Tree Swallows, although the swallow population remains healthy.

Several wooden birdhouses have been built along the walk to encourage species like tree swallows, house wrens, kestrels and barn owls to nest in the preserve.

The large Tree Swallow (Tachycineta bicolor) flocks here.

Nest competitors include Mountain Bluebird (Sialia currucoides), Tree Swallow (Tachycineta bicolor), and European Starling.

The Tree Swallow (Tachycineta bicolor), is a migratory passerine bird that breeds in North America and winters in Mexico, Central America and the Caribbean.