Common nighthawks (Chordeiles minor) are crepuscular birds that eat flying insects. You’ll spot them swooping and wheeling like aerial acrobats to catch bugs in mid-air. They are closely related to whippoorwills with the same teeny beaks that open wide into surprisingly enormous insect-catching mouths.
Common nighthawks are famous for two sounds. The first is a call often transcribed as a peent or beard sound. The other is a resonant booming noise that the male makes during courtship. The male climbs and then steeply dives. Near the bottom of the dive, air rushing over his wing feathers produces a vibrating boom, which sounds like a bellowing bull or a bullfrog. Listen for these sounds here.
Despite the name nighthawk, these birds are neither hawks nor are they nocturnal. They are most active when insects are most active — at dawn and dusk. Birders often call them bullbats for their batlike behavior and bull-like courtship noise. They are members of the nightjar family. The name nightjar originated in Europe: night refers to the birds’ activity near nightfall, while jar refers to the jarring call of the European nightjar. They have historically been called goatsuckers, from European myths that these birds sucked milk from goats at night(!?)
Nighthawks are ground-nesting birds that lay eggs on open fields, burned-over woodlands, pastures, or along stony beaches. In 1927, ornithologist Edward Howe Forbush noted of a ground nest:
The eggs so closely resemble the rock, earth or gravel, on which they rest, and the young so simulate in appearance clods or horse droppings covered with mold that they seem to escape the eyes of their enemies. The mother sitting on her eggs is almost invisible, as her plumage blends into the colors of her environment, and she will sit there with eyes nearly closed until almost trodden upon.
A female nighthawk does not actually build a nest. She selects a nesting site but doesn’t do anything to it except for laying two eggs. When the female pulls or pushes the eggs under her body to incubate them, the eggs shift position—sometimes moving five or six feet from their original spot during the approximately 18-day incubation period.
When people began constructing buildings with flat-topped tar roofs covered in gravel in the late 1800s, nighthawks decided that nesting on these roofs was a fine addition to their repertoire. In the 1870s, people noticed nighthawks nesting on gravelly mansard roofs in Boston. They nested on gravel roofs in Cambridge and Somerville as well. However, the gravel roofs of yore have mostly been replaced with smooth rubber roofs, which nighthawks shun as nesting sites. In addition, scientists have not documented a ground nest in Massachusetts since 1982. This means that nighthawks never (or almost never) breed in Massachusetts these days. We see them only during their migrations.
These birds are a sight to see during migration. From mid-August to early September, common nighthawks soar above Massachusetts on their travels to the Caribbean or South America. Their route is one of the longest migrations made by any North American bird. They leave their northern breeding grounds by the thousands, funneling their way along river valleys. In Massachusetts most are found streaming along the Connecticut River valley, but some can be spotted on the extreme eastern edge of their migration route along the Mystic and Charles rivers. Nighthawks are a joy to watch as they maneuver unpredictably to scoop up moths, flying ants and other insects out of the dark sky. Visitors to Fenway Park in August may notice these birds feeding on moths beneath the stadium lights above the outfield. At Mount Auburn Cemetery, watchers counted 432 migrating nighthawks on August 22, 2000. Since then, there has been only one migration-watch day that observers didn’t see nighthawks—and that was way back in 2008.
If you want to see migrating nighthawks cavorting in the sky, you might want to join a watch party at Mount Auburn Cemetery, with Mass Audubon, the Brookline Bird Club or the Boston Birding Festival.
If you prefer to look more informally, head to open areas near Fresh Pond or the Mystic River on a warm evening with lots of insects. Beginning about 30 minutes before sunset and continuing until 30 minutes after, scan the horizon for the silhouette of long-winged birds flying erratically. You may spot white flashes on the wings. Listen for the nasal peent. The birds may circle repeatedly over a patch of insects or linger over floodlit fields. Good luck!
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