Featured Bird Species: Tree Swallows


Featured Bird Species: Tree Swallows and other swallows

Family Hirundinidae

(Tachycineta bicolor)

As we walk along the Backshore after a remnant rainstorm from Hurricane Laura, we notice more Tree Swallows than usual (300+ over the South shore and 100+ over Whaleback), flying along the shoreline, likely hunting for flying insects. They dart quickly one way, then another, seemingly at random. Throughout the summer the numbers of Tree Swallows on Peaks Island has been relatively small, perhaps 12-20 near Battery Steele. And now they are abundant. Why?

As we look closer, we notice that some of these aerial acrobats are Barn Swallows, not only Tree Swallows. The two species are easily distinguishable in a bird identification book, but in the field where they fly so erratically, it is difficult to focus on individuals. Here are the characteristics that we finally use to tell them apart: Tree Swallows are white underneath, dark above, with relatively short-notched tails. Barn Swallows are also dark above, however they are noticeably larger, light brown underneath, with long, deeply forked tails. After studying them for a while, distinguishing them became easier. But are we oversimplifying things? A look in Peterson’s or Sibley’s field guide shows that there may be 5 species of swallows in this area during fall migration. Are the other three species (Bank Swallows, Cliff Swallows, and Rough-winged Swallows) also among these swarms of swallows?

Did we say fall migration? It’s August! Bird migration actually begins in late summer. Sandpipers and plovers have been observed here (please see 2020 Bird Lists) in recent weeks searching for food along the sandy and rocky shores. You may have noticed Monarch butterflies over the past several weeks; that plants are flowering; and that there are a lot more berries and rosehips. Many bird species are making the best use of these energy-rich foods as they migrate to their winter homes.

Most recently (August 28) we see swarms of swallows over Battery Steele marsh. Among the Tree Swallows and Barn Swallows, as described above, there are groups of swallows with lighter feathers, perched together on low shrubs within the marsh. We, and two other birders (Janyce and Mere), see that they are young Tree Swallows:

They form a cohesive group, apparently preferring their own company to that of their parents. They preen, they fly, they return to the same shrub, and they repeat this performance over and over. So, why all the flutter? Do they all migrate southward as a group? Where do they go?

During the end of August and throughout September, migrating groups of Tree Swallows (from the northern states and provinces) assemble on marshes at the mouth of the Connecticut River forming one huge mega-flock (CT River Tree Swallow Roost). During the day this mega-flock breaks into smaller groups to feed. At dusk they return to these marshes creating a huge swarm of birds flying over their roost before descending.

Once all groups arrive (one million birds in all) the swallows swirl and spiral vertically like a tornado, descending into their nightly roosting area.

This final event lasts only minutes,

however it is so spectacular that people aboard commercial dinner cruises, kayaks, canoes, and boats all gather to watch.

By the end of September these birds take another leap into their migration pattern. They break into smaller loose groups that move south during the day feeding ‘on-the-wing’. At the end of the day these smaller groups find new roosts to rest overnight – similar to finding a hotel room at the end of a long day on the road. The Tree Swallows continue this pattern until they reach their winter homes (See Distribution below)(1). It can take up to 3 months (2).

So what happens to the flocks of Tree Swallows we see here on Peaks Island? Do they maintain their integrity as a group after they merge into other larger flocks, such as the CT River assemblage? Or do they intermingle into different flocks with others? Do the young Tree Swallows we see here, stay in their original flock? With their parents? Are there other mega-flocks along the coast?

Some facts about Tree Swallows (1):

The adult Tree Swallow is 12cm (5 ¾ inches) long and may live to 12 years.

Distribution:

The Tree Swallow breeds throughout north and central North America spends the winter in southern USA coast, West Indies, and Central America to the northern coast of South America.

Plumages:

Male: Glossy blue-green back and white under parts with blackish tail and wings. Under wing is grey-brown. Tail is short and slightly forked:

Adult Female: More dull (less blue and iridescence) than male; occasionally a female has a brown forehead:

Juvenile: Brown upper parts and grey-brown wash on part of white breast:

First year female: Brown above with some blue feathers:

Second year female: Less brown and bluer feathers.

Call:

Very variable depending on the situation – different calls for various activities. Generally their song is clear with sweet whistles. While in large flocks the calls are thin and scratchy tzeev notes (3).

Habitat:

Tree Swallows prefer open areas near lakes, marshes, coastal areas where they feed in the lee of the wind. Marshes and trees are preferred for roosting.

Food and Feeding:

Tree Swallows prefer insects but they will eat mollusks, spiders, some fruit, berries (bayberry) and seeds (bulrush, sedge, bayberry and smartweed). They forage singly or in groups. Large numbers gather at insect swarms.

Breeding:

They arrive in early spring in Maine when seeds and berries are available. Other swallows that focus solely on insects in their diet arrive later.

The male courts the female with a vertical-display posture followed by flying to the nest giving a high-pitched call. Tree cavities are used for nests as well as man-made nest boxes. The nest is built of grass, pine needles, moss and aquatic plants, formed into a cup lined with feathers. Starting in early may to mid-June the female incubates 4-7 eggs for ~14-15 days. The male and female provide the chicks with 10-20 feedings per hour. The chicks fledge in 18-22 days.

Fledgling Behavior:

This story is about the behavior of Tree Swallow fledglings as provided by Michael LaCombe. He tells a story that is not available in a textbook, it only comes from closely watching bird behavior in the wild - in this case at a lake in Maine. We want to share it here:

"When fledging time arrives some two to three weeks after the clutch hatches, the most courageous chicks launch themselves out into the world first, while their more cautious siblings prefer to lounge in the nest and be fed by mom and dad. But the parents will have none of this. So the parent appears at the edge of nest with the largest of mayflies, teases, entices, the lazy chicks to leave home. Now the chicks begin to soar, bank, and dive. They are not taught to do this by the parent birds. It is instinctual. A parent hovers in place, with that choice mayfly, and feeds the young on the fly.

On one particular magical day, I watched them all day long, some six feet or so from the cavity nest, watched in amazement as the chicks launched themselves, as a parent finally got Lazy Larry to leave the nest, and I saw an amazing bit of behavior. When the soaring chicks tire, they naturally have thoughts of home and nest. But a parent stations itself at the entrance, white chest puffed out, and forbids entry. If they wished to rest, well then, they may just find a branch or bush to do so. But not for very long. With migration time approaching all too quickly, these chicks must develop their pectorals, perfect their skills at catching lunch on the wing, and ready themselves for the trip to south. A parent heads for the bush, hounds the resting chicks, and follows them in the air, coaching them to persist."

(PW and ML saw this same behavior in a parent kestrel with her two chicks at Greenwood Gardens down front.)

____________________________________________________________

References:

1. del Hoya, J, A. Elliot, and J. Sargatal. Eds. 2004. Handbook of the Birds of the World. Vol 9. Cotingas to Pipits and Wagtails. Lynx Edicions. Barcelona.

2. Weber, Charlotte. 2017. 1 Million Tree Swallows Prepare for Connecticut's Annual 'Avian Ballet"; NPR, wshu

3. Sibley, D.A. 2000. National Audubon: The Sibley Guide to Birds. Alfred A. Knopf, NY.

We dedicate this blog to Eleanor Morse – for her inspiration.

By: Sam and Patty Wainright

Photos © Patty and Sam Wainright

Reviewers: Michelle Brown and Marty

If anyone has answers to our questions or comments please contact us! patty@wainright.org or sam@wainright.org

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