American Tree Swallow Breeding Behaviors

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In early spring, just as the sun starts to warm the land and green sprouts poke through the cold earth, American Tree Swallows migrate north from wintering in the south. Flying many miles during the day, they migrate to northern North America in search of breeding grounds.

Tree Swallow breeding commonly takes place in man-made bird boxes, making them an easy bird to attract to your garden. In fact, this species greatly benefits from bird boxes, as they have to compete with other cavity-nesting birds, such as house sparrows, bluebirds, and woodpeckers.

Tree Swallow in Nest Box
Image by Elm Street Photography via Facebook / Website

The Tree Swallow is a stunningly beautiful bird, as their shining blue-green feathers and crisp white chests are unlike any other, making them a wonderful bird to witness in a bird box. But before we dive into the specific nesting habits of this special bird, let’s get acquainted with who this bird is, including its description and characteristics. That way, you can confidently identify it as a Tree Swallow if you have one visit your bird box.

How to Identify a Tree Swallow

Tree Swallows (Tachycineta bicolor) are a small bird in the swallow or Hirundinidae family. They are characterized by their stunning, iridescent blue-green feathers and their particular swooping and diving flight patterns.

Tree Swallow with Juvenile
Image by Heather Rose Assal ©

They are acrobats of the sky, flying gracefully in astounding displays of steep dives and quick turns to catch their unsuspecting prey, which consists mostly of flying insects. Because of this, they prefer open areas near water, such as meadows, rivers, marshes, and lakes, which attract breeding insects.

Their species name, bicolor, denotes the dark blue-green feathers on their back and white feathers below. They can look slightly similar to Barn Swallows (Hirundo rustica) but are easily distinguished by their chest colors; Tree Swallows have clean white chests and bellies, while Barn Swallows have a more rustic brown color, hence their species name.

Tree Swallow Breeding Habits

Tree Swallows breed throughout most of Canada (up to tree line) and in parts of the United States. Their breeding range in the western United States typically extends from northern California over to Colorado and up to Alaska. They also breed in the upper midwest from North Dakota to Michigan and throughout the Northeast, down to Pennsylvania. It is uncommon for them to breed in the central midwest and southern United States, preferring somewhat cooler climates to raise their young. 

Image by Elm Street Photography via Facebook / Website

Breeding occurs between May and September, and they have one brood per year. Males usually arrive at the breeding area before the females to search out potential nest sites.

As cavity nesters, the male looks for natural cavities in standing dead trees or abandoned Woodpecker nests. They will often nest in man-made bird boxes, building eaves, or even holes in the ground (probably as a last resort if there are no cavities available). Nests are usually chosen in areas near water or open meadows where there is plenty of food to feed the chicks.

Part of their courtship involves the male Tree Swallow showing the female various nesting sites. He will do this by perching near the nest holes or on top of the bird box. He will do flutter flights and bowing displays in front of the female, hoping to impress her with his charm and nest-finding skills.

Typically, one male mates with one female, though they don’t mate for life and will choose new partners each year. Plus, Tree Swallows aren’t always monogamous, and one male may mate with two females, or a female might mate with another male. It is not uncommon for chicks in a single nest to have different fathers.

While they fly in large groups when migrating, Tree Swallows disperse to find their breeding partners and aggressively defend their territory once a nest is selected.

How do Tree Swallows Build Their Nests?

Once the playful courtships have ended and nest sites have been chosen, the female builds the nest with dead grass, moss, rootlets, and other small, fibrous materials. She begins her work with the outer circumference of the nest and uses her feathers to push out the material to shape it into a cup.

The female tree swallow does this repeatedly; as she adds new material, she pushes it out with her wings so that there is an indented cup area for her to lay her eggs. The last layer of the nest is lined with soft feathers. Nest building can take anywhere from a few days to over two weeks.

Once the first layer of feathers is laid, the female will lay her first egg. She lays one egg per day and will lay about 2-8 eggs (5 is average). The eggs are pale pink at first and then turn to pure white within the first few days of being laid. The male and female continue adding feathers to the nest after the female lays the eggs.

Incubation and Nestling

The female Tree Swallow incubates the eggs for about 11-20 days. It is common for the female to periodically leave the nest – sometimes for several hours on warm days. All the eggs hatch within a couple of days, and the mother will take the eggshells out of the nest as the chicks hatch.

Image by Nest Box Live

Both the male and female feed the hatchlings. The chicks are born helpless with closed eyes and pink skin sparsely covered in downy feathers. For the first few days after they hatch, the female broods them to keep them warm. As the hatchlings mature, the chicks’ downy fuzz thickens into dark black-brown feathers, and the mother starts to spend less and less time with them.

The hatchlings stay in the nest for about 15-25 days, miraculously growing into fledglings able to take their first flight upon leaving the nest. They leave the nest one at a time, with all the fledglings leaving within one to two days.

Image by Nest Box Live

After they leave the nest, both parents will continue to feed the fledglings for a few days. Because they mature quickly, the fledglings will reach adulthood and breed by the following spring.

Watch the full video of the Tree Swallow breeding cycle on Facebook.

How To Encourage Tree Swallow Breeding In Your Garden?

It’s one thing to learn about the fascinating nesting habits of tree swallows, but it’s another thing to see it firsthand – in real time!

With our Nest Box Live – AI-Powered Bird Box, you get the unique and incredible opportunity to witness birds choosing your bird box, building their nest, laying eggs, and raising their young.

While you can’t be certain what species of bird will choose your bird box, chances are high it may be a tree swallow if you live near its ideal breeding habitat. If so, you’ll have a wondrous opportunity to see what was described here in action and become intimately familiar with the spectacular Tree Swallow.

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