(Editor’s note: Ron Ketter is a member of the Talbot Bird Club and a Maryland Ornithological Society board member.)
Once young tree swallows approach full size, the young stick their head completely out of the nest opening, begging for food. At this stage, adults may deliver food either in mid-flight or by landing briefly on the outside of the nest. (Photo by Ron Ketter)
Tree Swallows are commonly found on the Eastern Shore during spring and summer months.
One of six swallow species that can be found in North America, their breeding range extends across the northern part of the United States and into Canada.
Tree Swallows are often seen swooping above water, marshes, or open fields.
When not in flight, you might spot them perched on power lines, especially during late summer and early autumn.
They mainly eat flying insects, including flies, bees, mosquitoes, wasps, dragonflies and butterflies.
While insects represent most of their diet, they can also subsist on berries during colder weather when insects are hard to find.
Tree Swallows have a two-tone appearance, dark above with white underparts.
This, along with their flight behavior, led to their scientific name Tachycineta bicolor, which means “two-colored moving quickly.”
Adult males have blue-green on their backs, extending to the top of their heads and face, often with an iridescent sheen.
Their body is bright white below, extending from the chin to just short of the tip of their tail. They have black wings and a thin black eye mask.
They have long pointed wings, and their tail is square or shows only a slight notch.
Adult females are duller and show some brown on their back, while juveniles have completely brown backs.
Both are white below.
Tree Swallows seek mature or standing dead trees with old woodpecker holes or natural cavities for their nests.
Over the last half century, they have readily taken to using nestboxes built for bluebird conservation purposes.
Currently, these artificial nest boxes are estimated to host two percent of all Tree Swallow nests.
Only the female Tree Swallow builds the nest.
She collects grass from the ground and carries it in her beak to the nearby cavity.
She uses her feet and body to shape the grass into a cup measuring two-to-three inches across and one-to-two inches deep.
Once she completes the nest cup, both she and her mate gather feathers to line the nest.
These feathers help insulate the eggs and recently hatched nestlings.
Once the nest is finished, which takes between a few days to a couple of weeks, the female lays from four to seven eggs.
The female is solely responsible for incubation, which may take as few as 11 days in warm weather but may take up to 20 days during cold spells.
After the young hatch, both the male and female feed the young.
This is a very busy time for them.
They work 15 hours a day, making around 300 visits each day bringing food to the nestlings.
This goes on for about three weeks as the nestlings grow from an average of 1.6 grams to 21 grams, the same size as their parents.
The young are initially fed small insects.
Adults have developed an efficient way of capturing a large quantity of small insects, such as mosquitos or small flies, in their open mouth.
As they do so, they push the insects to the back of their throat and mix them with saliva and sticky mucus to create a soft, chewy mass called a “bolus.”
Once the bolus reaches a sufficient size, adults return to the nest to feed their young.
During peak feeding demand, adults capture 6,000 to 7,000 insects a day this way.
As the nestlings grow larger, adults feed them larger insects, such as dragonflies or wasps.
Right after the young hatch and are quite small, adults enter the nest completely when delivering food.
As the young grow, adults land at the nest opening and lean in to feed them. Once they approach full size, the young stick their head completely out of the nest opening, begging for food.
At this stage, adults may deliver food either in mid-flight or by landing briefly on the outside of the nest.
The young fledge after about three weeks and receive varied level of care from their parents.
While some receive a few days of continued feeding, others become immediately self-sufficient.
Tree Swallows are quite social, forming large flocks in mid-to-late summer.
Tens of thousands congregate in marshes or fields near a river or the shore as they prepare for migration.
Tree Swallows mostly overwinter along the southern coasts of the United States, in Florida, as well as Mexico, Cuba and Central America.
They occasionally are found on the Eastern Shore during winter due to their ability to digest the waxy berries from bayberry shrubs.
Although still rather common, the Tree Swallow population has decreased by 30 percent since 1966.
This is most likely due to the loss of natural tree cavities from land management practices that remove mature and dead trees.
Leaving dead trees standing or installing nest boxes is a way of attracting this species.
