The Swallows of Autumn
By Kenneth Turner Blackshaw
We often think of swallows as harbingers of spring and their early arrival gives us hope that winter is on the run. But, it is in the autumn that they give the mightiest show and catch many a birder's attention. Over the past few weeks, thousands of Tree Swallows have been congregating over the ponds on our South shore.
Tree Swallows are charming, graceful, little swallows with dark backs and pearly white undersides. If you are fortunate enough to see one at rest, as we often do when they are investigating a bird box, they provide a stunning sight. Our bird watching group did this late last March, actually putting a 40 power spotting scope on the doorway of one of these abodes. The head and shoulders of a Tree Swallow filled the field. The shiny dark blue-green iridescence knocked our eyes out! Then there was the very sharp contrast between this color and the pure white of the throat, breast and belly. It reminds me of the color pattern on Killer Whales, and as far as insects are concerned, these are little flying Killer Whales.
Tree Swallows lack what most people think of as a 'swallow' tail, like the long, needle-like appendages of a Barn Swallow's tail. Tree Swallow tails are forked, but rather short, giving them a more chunky appearance than our Barn Swallows. In the summer on Nantucket, Tree's and Barn's are the two most common swallows to see and it is good to notice their overall shapes in addition to the color differences.
Swallows as a family spend most of their time in the air, catching insects on the wing. Tree Swallows in particular, catch huge amounts of mosquitoes so people like to have them around. Knowing this, it was all the more unusual for the Sunday morning bird group a few weeks ago. We saw thousands of Tree Swallows on the ground near Hummock Pond. These birds were sitting on a plowed field, and close study, again with a spotting scope, told us they were consuming very small bits they were finding there on the ground. It was hypothesized that they were gathering small amounts of gravel to use in their gizzards to assist in digestion. Other ornithologists have determined they often consume minute insects, almost too small to be seen, in this situation.
If you looked up in the air over the past few weeks, you would see ten to fifty swallows flying along, hunting as they go, but generally moving from East to West across the island. Our summer swallows are long gone this time of the year. The swallows we are seeing now have spent the summer in the northern part of their range, perhaps in Northern Quebec or Newfoundland. For some reason, a large percentage of the population heads east to the Atlantic coast, and then makes a right turn to go south. This is particularly true with birds that have hatched this year. Young Tree Swallows differ from their parents by being brown above instead of the blue-black color. They also have a wash of brown on the throat, fading into white on the breast. This makes them very hard to distinguish from other species of swallows, especially the Rough-winged. However that species is rare here and departs by mid-August so there is little room for confusion now.
So, a large portion of North America's Tree Swallow population is winging past our island. At times, the flocks over Miacomet, Hummock, and Long Ponds look like a swarm of gnats in the distance. Only when you put binoculars on them do you realize these are actually birds and much further away. To see perhaps 10,000 Tree Swallows in the air at once is an awesome sight. They swirl and spiral around as if caught in a giant whirlpool. The motion is so continuous and complicated, you wonder why no collisions occur.
Our Tree Swallows will be easily seen through the end of October and then head farther South where insects can still be found in the winter. The typical northern limit of the range is coastal North Carolina. Occasionally a few will linger on in Southern New England, but they have only been found once on Nantucket's Christmas Bird Count, when six birds were seen in 1969.
If you are out on Nantucket's South shore, keep an eye out for these swarms of gnats that turn out to be birds. Watch their graceful flight and imagine how our island must look to them as they whirl about. Then say 'farewell' and think about when they will return to a much different, 'little gray lady' as the first buds of spring are just starting to tint our brown winter landscape.
If you enjoy social birding, every Sunday a group meets in the parking lot in front of the Nantucket High School at 8 a.m.
To hear about rare birds, or to leave a bird report call the Massachusetts Audubon hot line at 888-224-6444.