With mosquito season nearing its peak after all our rains, so, too, will come the peak of swallows congregating on the coastal marshes in the next few weeks in preparation for their long journey south. The swallows have only started to gather on Plum Island and will peak by mid-August. Along the Parker River Wildlife Refuge on Plum Island, they cover the bayberry and beach plum on the dune side of the road and sit atop the cattails and reeds on the marsh side. Their numbers will climb into the thousands — they look like swarms of giant locusts as they take flight to feed. They often cover the road, forcing cars to stop and proceed at a crawl as the swallows disperse. They bring back memories of Africa when we watched the swarms of queleas cover the road, as well as every tree and bush in sight. Though the queleas were a hundred times more abundant (yes, hundreds of thousands), the mass of swallows that occur on Plum Island every August still conjure up those images.
On a mid-August day, you might find all six local swallow species among the numbers on Plum Island. The majority of the swallows here are tree swallows, probably making up 80 to 90 percent of the individuals. The adult tree swallows have a deep iridescent blue back and bright white front. The young tree swallows are brown on the back. These are the swallows that nest in the boxes that line the marshes in Essex County. Tree swallows are aptly named because they nest in cavities in trees. But a lot of their natural habitat has disappeared, and many tree cavities have been taken over by starlings and house sparrows. Nesting box programs have helped the tree swallow become more plentiful, which, in turn, helps curb the flying insect population around the marsh areas where they breed. Adding a nesting box to your yard if your live near a field or marsh might attract these beneficial birds to your yard in the spring. You may recall that we had a pair of tree swallows nesting in a house outside of our store a few years ago.
Barn swallows are the more evident of the remaining swallow species gathering on the island. Barn swallows have a blue back, rust throat, buff underneath and a deep forked tail with specks of white. These are the swallows that build mud nests on eaves and beams in barns, garages and other structures. Their droppings can create a mess noticeable in clean-kept barns on gentleman farms, but the majority of folks welcome these breeding birds by keeping a door or window open. The swallows return the favor by eating flying insects in the area.
Similar in overall coloration to the barn swallow, the cliff swallow has the same deep blue back, rust throat and light underneath. But it has a buffy patch on the rump and a square tail. They build a mud nest similar to the barn swallow, but cliff swallows usually nest in colonies on cliffs or under an open structure such as a bridge or storage shed. It is probably the least common of the five species, but local colonies can still be found, breeding under the Route 1 bridge over the Parker River and under the Plum Island bridge some years ago.
The bank swallow and rough-winged swallows are the two brown-backed swallows, the latter being the larger of the two. In addition to its noticeably larger size, the rough-winged swallow has light underparts and a dusky throat. It nests individually in cavities or crevices in culverts, old drain pipes, etc., but seldom in tree cavities like tree swallows. A pair has bred under Pike's Bridge in West Newbury in years past.
The bank swallow is a cavity nester like the tree swallow; however, as its name indicates, it nests in colonies in burrows on the side of a dirt embankment. These brown-backed swallows have a brown stripe across their pale chest. A few purple martins continue to nest on Plum Island. These deep blue/purple iridescent birds are the largest of our local swallow species. The female and immature martins are lighter in color underneath. Purple martins nest in colonies in the "condo style" martin houses erected on the refuge and elsewhere. All the swallows eat flying insects on the wing, which make them very beneficial. They are a critical part of the food chain that can help naturally control flying insect populations. So on a warm summer's evening as mosquitoes start to bite, the sight of thousands of swallows on the wing is a very welcome sight indeed.
Steve Grinley is the owner of Bird Watcher's Supply and Gift at the Route 1 traffic circle in Newburyport and the Nature Shop at Joppa Flats.