Swallows are small, speedy, short-winged aerial hunters with slender bodies and pointed wings and a tail, just like a jet airplane. The birds are quick and graceful in flight, often catching a variety of flying insects in midair during a long, dizzying air travel pattern near the water or in a meadow. These short-billed aerial hunters know exactly what they are doing. A single Barn swallow (Hirundo rustica) , for example, can consume 60 insects per hour, an amazing 850 per day. The small birds are surely one of Mother Nature’s most successful avian insect predators. They are not lazy birds either. Swallows can fly several miles from their nest site to forage for not only insects, but in some cases for spiders, snails, seeds and berries too.
A quick glance during sunset and you might think the birds were bats. The quick aerial feeding lifestyle of a swallow gives it some resemblance to a Little Brown Bat. Both hunt for insects and can dart quickly through the air, abruptly changing directions on the wing to catch a mosquito, fly, bee, or winged ant.
But as Dr. David W. Winkler, a professor and curator of birds at Cornell, points out in a July 16, 2002 interview in The New York Times there is a big difference in the way swallows and bats forage for food. “Swallows are definitely visual foragers,” and “hunt only until dark, when the bats take over.” While echolocation is used by bats to catch prey, Dr. Winkler goes on to explain that swallows have ultraviolet light vision. This helps the birds find insects, including moths and butterflies, which have body coatings that strongly reflect UV light. Their eyes could also be polarized to help spot an insect from long distances. With these important tools, “swallows can come back to the nest with up to 50 live insects in their mouths.”
One would think the birds are the best free, nontoxic pest control in the world. Yet, they cannot do it alone. With millions or billions of insects hatching out of eggs each summer, and with only a limited number of swallows in any one area, the birds can only really play a small role in mosquito population reduction. But this only means we need to increase the amount of nesting boxes, habitat and homes to expand the swallow population.
Each year several species of swallows migrate to nesting sites around New York Harbor. While not as famous as the “Swallows of Capistrano” in San Juan Capistrano, California, they are no less entertaining to observe during their spring arrival in April and during their fanciful feeding and breeding activates throughout late spring and summer.
In the past two decades I have observed generally five species of swallows nesting around the harbor: Purple martins (Progne subis), Tree swallows (Tachycineta bicolor), Bank swallows (Riparia riparia), Cliff swallows (Petrochelidon pyrrhonota), and Barn swallows. Occasionally a rough-winged swallow (Stelgidopteryx serripennis) will also be spotted near the water, but unlike most other swallows, the rough-winged species does not form colonies and is solitary in nesting to make it more difficult to study.
In greater profusion are tree swallows, which have taken advantage of the abundance of Blue bird houses in fields, marshes, and near shorelines throughout New York Harbor to build nests and raise young. The birds love to live near the water, where there is a wealth of flying insects for food. Tree swallows arrive early around the harbor in the spring, migrating from far away wintering areas in Florida or farther south into Mexico, Cuba or Central America. The birds can sometimes arrive to the harbor as early as March, usually after several days with temperatures above 60°F, providing hope that spring is right around the corner, but more importantly for swallows to stake out prime nesting territories.
Barn and Cliff swallows are also frequent birds around the estuary. Just the other day, I spotted about two dozen Barn swallows in flight at Sandy Hook NRA. They were quickly dipping down to a large wet field to take clumps of mud in their tiny beaks. As my grandfather used to say, “it’s a sure sign of summer when you see Barn swallows flying back and forth with mud in their beaks to a barn or building where they build a nest.”
Nowadays their nests can also be found under bridges or docks, or overhanging on decks and patios or built under eaves of buildings. Both Barn and Cliff swallows construct nests formed from mud pellets that they collect in their beaks. Barn swallow nests are cup shaped, while Cliff swallow nests are gourd-shaped. Both male and female will make up to 1,000 trips to collect mud and build a nest made of mud pellets lined with dried grass, hair, and feathers. But the birds do not stay long here, spending only enough time to raise a family. Southbound fall migration for Barn swallows to Central or South America may begin as early as mid-July around New York Harbor, and mid-August for Cliff swallows to South America.
Bank swallows are the smallest of our swallows, only about five inches in length. The small birds migrate to the harbor from Central America and are usually seen in flocks, nesting in sandy holes along streamside cliffs or in the bluffs on beaches. The birds prefer to nest in burrows excavated in a steep bank of loose soil using their tiny bills and small feet. It’s an amazing achievement when you consider one bird makes one burrow with no help. A male swallow will dig a burrow into the bank before he has a mate. When males have completed creating their burrows, females will then hover in front of potential nests to choose a mate and his nest site. Sometimes dozens of holes in a sandy cliff can be seen while paddling along a stream bank around New York Harbor.
From the smallest to the largest swallow. Purple martins, also a member of the swallow family, can reach up to 8 ½ inches in length. They migrate all the way from South America to exclusively nest in their own private home, a manufactured martin house placed in an open area near the water around New York Harbor. The birds learned a long time ago that the closer they nest to humans, the fewer predators will move forward to steal their eggs. As a result, much of the eastern North American population now nests completely in Purple martin housing. It’s like a condominium complex, with dozens of martins nesting in the same spot.
But this is a good thing. We need more homes and habitat for the swallows that call New York Harbor home during the summer. The Purple martin population has been declining around New York Harbor for several decades due to the loss of nesting sites.
This is true for other swallows as well. For example, North American Bank Swallow numbers declined by over 5% per year from 1966 to 2014, resulting in a cumulative decline of 94%, according to the North American Breeding Bird Survey.
Yet, population status can vary greatly. When the availability of good nesting sites and food are abundant then populations increase, but comprehensive development along waterways do not often take into consideration the needs of swallows and the poor birds often find themselves ousted from once prime habitat. Bad-mannered people who do not understand the needs of wildlife or dislike having birds nesting on or near their buildings or structure often destroy good nesting sites.
Even when favorable nesting locations for swallows are found, it’s often not easy being a baby bird. Nests may fall apart or young swallows may fall out of nests or die from nest infestations of parasitic insects and mites. Increasing predator populations in urban-suburban environments, including crows, starlings, house sparrows, domestic cats, and rats also play a role in decreasing significantly swallow populations by injuring or killing eggs and nestlings. Weather as well can limit the swallow population. The birds are sensitive to cold snaps that last more than three or four days. This makes it more difficult to forage for insects and many birds starve for the lack of food.
With all this stress, it’s anyone’s guess how long the swallows of New York Harbor can last. But for now, the birds are busy nesting and raising families that will hopefully keep this group of birds going on around this urban-suburban estuary.
Later in the year, the swallows will once again begin their long southbound migration to tropical climates to spend the winter. They often gather in large groups (sometimes as many as 2,000 birds) on telephone wires before departing. Swallows migrate during the day, foraging for food and continuing being successful insect predators along the way.
To view more pictures, video, or stories of wildlife around Sandy Hook Bay, Raritan Bay, and Lower New York Bay, please visit my nature blog, NY Harbor Nature at http://www.nyharbornature.com
Source: AH Herald, May 30, 2017
http://www.ahherald.com/columns-list/old-oak-trail/24213-the-swallows-o…
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