The swallows have started to gather on Plum Island and they will reach their peak by mid-August.

Along the Parker River Wildlife Refuge, they feed on the bayberry on the dune side of the road, and the constant flow of birds over the marsh and dunes all down the island are feeding on insects on the fly.

Their numbers will climb into the thousands, perhaps tens of thousands. They can be seen in large numbers sitting atop the cattails and reeds in the marsh and often look like swarms of bees or giant locusts as they take flight all at once to feed, especially near dusk.

The swallows will sometimes cover the road during the day, forcing cars to stop and proceed at a crawl as the swallows disperse. It is imperative that you drive slowly along the road during this time (as you should every day).

Unfortunately, the speed control signs do little to slow the cars that race to Sandy Point on these hot summer days, imperiling the swallows and other birds.

On a mid-August day, you might find all six local swallow species among the large numbers on Plum Island. The majority of the swallows here are tree swallows, probably making up about 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 some of the Great Marsh in Essex County.

Tree swallows are aptly named because they nest in cavities in trees. 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. Unfortunately, the refuge no longer continues to erect or maintain the boxes that use to be scattered about the Salt Pannes area.

Adding a nesting box to your yard if you live near a field or marsh might attract these beneficial birds to your yard in the spring. We even had a pair of tree swallows nesting in a house outside of our store on Route 1 many 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. Though their droppings can create a mess in the clean-kept barns on gentleman farms, many barn owners still welcome these breeding birds by keeping a door or window open. The swallows return the favor by devouring the 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. It has a buff 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 small local colonies can still be found, most recently under the Derek Hines Bridge in Amesbury.

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, or in old drain pipes. We had a small colony of rough-winged swallows nesting in the drainage holes of storage trailers in Salisbury some years back.

The bank swallow is the smallest swallow we have and it is a cavity nester like the tree swallow. However, as its name indicates, it nests in colonies in burrows on the side of dirt embankments. These brown-backed swallows have a brown stripe across their pale chest.

The purple martins were through nesting at Lot 1 on the refuge a few weeks ago and many have already migrated. 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 in the area and don’t mind nesting close to humans.

All the swallows eat flying insects on the wing that make them very beneficial. They are a critical part of the food chain that can help naturally control flying insect populations without the need for spraying.

So on a warm summer’s evening, as mosquitoes start to bite, the sight of thousands of swallows on the wing is a welcome sight. It is one that you should experience before they all head south.

Steve Grinley is the owner of Bird Watcher’s Supply and Gift at the Route 1 traffic circle in Newburyport. Email him at Birdwsg@comcast.net, or view website: www.birdwatcherssupplyandgifts.com.

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