Disappearing Bullbats

Years ago I used to hear the nasal “peents” of bullbats, also known as common nighthawks, as they flew over First Field at dusk on summer evenings.

During the 1970s, 80s, and 90s, we heard or saw a few most years, and back in July 1987, four nighthawks appeared every evening, “peenting” and swooping low in the company of a couple barn swallows and bats.

My husband Bruce and I also remember when he spotted four nighthawks over First Field on June 28, 1991, sifting the air for insects. We even noted the notched tails, white wingbars and throats of these gray-brown, big-eyed, wide-mouthed birds.

Throughout the 1990s, we continued to hear or see one to three common nighthawks most years, but in this century the only records we have of them are of one calling at 5:30 am on May 22, 2007, when our son Dave and I were conducting an Important Bird Areas Count on our property and on June 8, 2020, when our son Mark heard a nighthawk “peenting” in early morning along with calling whip-poor-wills.

A member of the nightjar family and closely related to whip-poor-wills, the name “nighthawk” was poorly chosen because these birds are not hawks and they hunt at dawn and dusk, not at night. Their other name—“bullbat”—refers both to the booming sound their wings make during their courtship flights and their erratic, bat-like flying.

Even the “common” in their name has become “uncommon” throughout their continent-wide, breeding range in North America, especially in northeastern United States and Canada. According to the North American Breeding Bird Survey, from 1966-2014, common nighthawks declined 61% throughout North America and the 2014 State of Birds Report labels them a “Common Bird in Steep Decline.”

In Pennsylvania, between our first atlasing (1983-89) and second atlasing (2004-2009) of breeding birds, Greg Grove, who wrote the common nighthawk account in The Second Atlas of Breeding Birds in Pennsylvania, pointed out in an email to me that “of all species with significant populations, nighthawks had the greatest decline in block detections from atlas one to atlas two,” — the number of blocks dropping 71% with only four confirmed records of nests containing eggs or young. For this reason the common nighthawk is now considered “Near Threatened” by the Ornithological Technical Committee of the Pennsylvania Biological Survey and a Pennsylvania Species of Greatest Conservation Need in the Pennsylvania Wildlife Action Plan.

Douglas A. Gross, in a 2013 article he wrote for the American Birding Association “Decline of the Bullbat,” recalled watching several nighthawks over his yard in Bloomsburg on summer evenings when he was a youngster in the 1960s. He believed they nested on the flat roofs of mills and other flat roofs in the town. However, he returned to his old neighborhood several times during the second atlasing period, and he didn’t see or hear a single nighthawk.

“They’re gone,” he wrote. “The community is poorer for it.”

Researchers hypothesize several reasons for their decline including lower numbers of flying insects because of pesticides and habitat loss such as open woods in rural areas and flat gravel roofs in urban localities.

Throughout North America, nighthawks use a number of habitats, but all are open and flat enough to hold the two white to pale gray speckled eggs the females lay on the ground, from rock outcrops to woodland clearings.

But in many places nighthawks became dependent on flat, gravel roofs, and when they were replaced by rubberized roofs, nighthawk eggs were no longer camouflaged, they rolled easily, and the rubber was hotter than gravel in the sun which may have been damaging to the eggs and later the chicks.

Daniel W. Brauning, in the first Atlas of Breeding Birds in Pennsylvania, wrote that common nighthawks were “almost totally restricted to manmade structures [for nesting] in Pennsylvania,” a practice that went as far back as 1869 when W.P. Turnbull mentioned nighthawks nesting on flat gravel roofs in Philadelphia.

Still, Grove wrote in his account, that one nesting site was on a former surface mine area in northern Clinton County and another in Carbon County on a newly-grassed area that had been denuded by industrial pollution. Other suspected nesting sites were found on former surface mines in Centre and Clearfield counties and in the coalfields in Schuylkill, Lackawanna, and Luzerne counties.

Because of a long migration back from Brazil, where most common nighthawks winter, they don’t arrive in Pennsylvania until May. The male performs courtship flights in which he flies down to within a few yards of a female and then turns sharply upward. His vibrating feathers produce a booming (or bulling) sound. Then the male lands beside her, spreads his tail, and sways back and forth, displaying his swollen throat and large white neck patch, while he emits guttural croaking notes through his closed beak. He also flies over the female repeatedly and “peents.” Eventually, they mate.

But he continues these flights and displays throughout the time his mate selects the nest site, lays her eggs and incubates them 16 to 20 days, usually in late May or early June in Pennsylvania. Once his offspring hatch, he starts feeding them regurgitated insects at dusk and dawn while the female continues brooding them for 15 days, although as the young mature she also hunts food for them.

Nighthawks use their wide-open mouths to capture as many as 50 species of insects on the wing including what seem to be their favorite–queen flying ants– as well as a many kinds of beetles, true bugs, flies, caddisflies, crickets, and moths. One nighthawk stomach examined by researchers contained 2,175 ants and another 500 mosquitoes.

After they hatch, nestling nighthawks can hold their heads up and open their eyes, and they are covered with soft down. For those reasons, they are considered semiprecocial or partly helpless instead of totally like songbird nestlings. By their second day they respond to the female’s call and move around. Most of their feathers have developed at 16 days when they hop up and down and they begin flying at 18 days. At 25 days of age, they can feed themselves while flying and they leave the care of their parents at 30 days old.

By the third week of August, common nighthawks begin their migration south and birders sometimes count nighthawks flying overhead in open areas an hour or two before sunset. Back in 1999 Greg Grove counted 270 common nighthawks flying over Lake Perez in Huntingdon County and in 2006 100 foraging over fields near McAlevy’s Fort, also in Huntingdon County.

Sometimes more formal Common Nighthawk Watches are held by organizations, for instance, the West Chester Bird Club hosts a series of nighthawk watches during the last week in August and into early September at Bucktoe Creek Preserve in Kennett Square.

Common nighthawks migrate throughout the day in large flocks and most were thought to go by way of Mexico and Central America and then on down through South America to Brazil.

But a new study, published in Ecography: A Journal of Space and Time in Ecology, used GPS data and transmitters to track common nighthawks. The study was led by researchers from the Smithsonian Migratory Bird Center (SMBC), the University of Alberta, and Environment and Climate Change Canada, and tracked 52 individual nighthawks from 12 breeding populations across Canada including Quebec, New Brunswick and Ontario in eastern North America and in South Dakota, Oregon, Arizona and Texas in the United States. They found that nighthawks from throughout the continent flew east or west to congregate in the Midwestern United States along the Mississippi flyway. From there they mixed together and took a common migration route south across the Gulf of Mexico to Colombia and down through the northern Andes, to reach their wintering grounds, mostly in Brazil.

As part of the Smithsonian’s Migratory Connectivity Project, the researchers plan to concentrate on the times and places of where common nighthawks are during breeding, fall migration in North America and before they cross the Gulf of Mexico during spring migration and hope by their studies to find out why nighthawks are declining. But as Elly Knight, lead author of the study and doctoral student at the Department of Biological Sciences at the University of Alberta, said in an article published by the Smithsonian MBC, “figuring out what causes these declines can be difficult and complicated for migratory species like the nighthawk because they occupy so many different places during the year.”

In the meantime, some conservationists are trying to entice breeding common nighthawks to nest on flat, rubberized roofs by placing gravel corners on them with the permission of building owners and by clearing patches of forest for open nesting sites. But pesticide use must also decline so that the aerial insects they depend on can once again provide food for them and the other birds and bats that also need flying insects to survive.