Booming Bullbats: afield with the Common Nighthawk

Common nighthawk in flight, D.S. Hall.

It was just after 2 o'clock in the morning. I slowly drove the bumpy road under a moon which was full just two days earlier. Clouds of dust trailed and swirled in my rearview mirror like red spectres illuminated in my tail lights. The sky was brilliantly clear and, being so far from any streetlights, every star was visible. The barrenlands afford spectacular night sky views since trees are so scattered and few. This landscape is also prime territory of nighthawks, who nest in areas of open country.

I'd been out the entire night surveying for nightjars and had so far come up disappointingly empty-handed. I had high hopes of this changing as I made my way into a local nightjar hotspot in Downeast Maine. Up ahead, the road curved towards a stand of tall pines surrounding a small lake. Quiet camps were crowded together along the shore, the only structures I've seen in miles. Coming to a halt, I could hear a raucous night chorus underway before even leaving the car. Whip-poor-wills singing ceaselessly and Barred owls caterwauling (a strange, monkey-like vocal exchange between owl pairs). All through the sky, Common nighthawks darted, calling their raspy"peent!... peent!... peent!" calls over the barrens and forest alike. Working my way back up the roadway, I made a series of stops along the road to listen for nightjars and was not once disappointed. As in past visits, nighthawks and whip-poor-wills both abounded.

Off in the distance, the first light of day peaked above the horizon. The sun's earliest rays manifested as a dull, yellow seam between the deep blue tapestry of the waning night sky and the sprawling, ink-black landscape of the heath. The clock was ticking and night's end was near. The nightjar's nocturne would very soon give way to a dawn chorus of songbirds. The nightbirds would use their plumage to disappear to a day of silent, motionless rest. My final stop was just before 4 o'clock and well-timed to witness the last hurrah before the sunrise. From the barren-side thickets, the songs of the Eastern whip-poor-wills overlapped and quickened pace. These were birds in competition, taking advantage of the final opportunity to prove their vigor before the bulk of the birdlife awoke to usurp the airways. In among their repetitive chants, a sweet and melodious song joined in. The singer was the Vesper Sparrow, a ground-dwelling songbird of open country named for its habit of singing late into the evening, long after other daytime birds go silent. The Vesper Sparrow sings at both ends of the day and will begin at the very first glimpse of the rising sun. Within our state, this sparrow is mostly restricted inland to within 50 miles or so of the Maine coast. Where there are agricultural lands and dry grasslands, these birds can be numerous. The blueberry heaths of Downeast Maine host many of these sparrows each summer making them a common associate of our nightjars.

Flying at dawn, M. Nenadov.

As the sky begins to lighten, the nighthawks became visible as graceful silhouettes soaring to and fro above the barrenlands and calling more vigorously than ever. As birds of the twilight, this was their hour. Then they started "booming".

The boom of the nighthawk is one of the most fascinating sounds in nature. This rushing noise sounds somewhat like being passed by a speeding car. The "boom" is produced by male nighthawks for a diverse array of communicative intentions. It is used as part of a courtship display to attract mates, to lay claim to breeding territories, and to chase off potential nest predators. Perhaps what is most interesting about the "boom" is that it is a mechanical sound and not a vocalization. The sound is produced by a flying nighthawk performing a sharp nose-dive, swooping upwards before reaching the ground, and flexing his wings downward. Air passing through these outstretched flight feathers makes a loud "vooosh!" that can be heard over long distances. Several nighthawks looped through the air, their bold, white wing patches now visible in the earliest morning light. As I stood and took a recording of all the activity, a nighthawk dove and boomed just a few feet above my head. My presence had been noted and I was welcome no longer. This is no surprise. This landscape is just the habitat nighthawks seek for their nesting grounds and they are very protective of their nests and young. Sorry to leave all the excitement behind, but wanting to respect their space, I departed for home.

Common nighthawk, N. Myatt.

Nighthawks are highly interesting birds with many attributes which set them apart from many of their fellow nightjars. The term "nighthawk" is a bit of a misnomer in that this bird neither nocturnal (they are actually most active at twilight) nor are they hawks. Rather, nighthawks are a subfamily of 10 species within the nightjar family found only in the Americas. Their scientific name, Chordeilinae, roughly translates from Ancient Greek to "evening dance", no doubt inspired by their graceful flight and conspicuous twilight displays. The timing and character of their bat-like flight has also earned the Common nighthawk the local moniker "bullbat". It is not uncommon to see nighthawks foraging in the company of bats as both animals are twilight predators of flying insects. Unsurprisingly, nighthawks are also locally referred to as "bugeaters". Nebraska supported so many "bugeaters" in the late 19th-century that the university's football team was named in honor the birds. Most regrettably, but understandably, they switched to the "cornhuskers" just one year later. Perhaps it's better to be known for husking corn than eating bugs, but a nighthawk would make for a great mascot...

Unlike whip-poor-wills and chuck-will's-widows, who both sally forth after prey from perches, nighthawks actively chase down and capture insects in the air. Flying ants, beetles, moths, and caddisflies are all regular parts their diet. To drink, nighthawks skim water from the surfaces of lakes, rivers, and ponds while in flight. These birds will regularly forage in developed areas at night and capitalize on the large number of insects drawn to street lights, stadium lighting, and other outdoor lights. More populated areas can be risky places to hunt, however, and nighthawks resting on or foraging over roadways are sometimes struck and killed by cars. Hunting over sports fields is evidently not without its risks as, in 1984, a nighthawk foraging over Milwaukee County Stadium was struck and killed by a flyball during a baseball game!

In terms of appearance, Common nighthawks have a number of attributes that set them apart from New England's other nightjar species. While whip-poor-wills have shorter, rounded wings for flying through forests, Common nighthawks have long, pointed wings that make them swift and acrobatic aerialists. While all nightjars have cryptic plumage, nighthawks have bold white patches on their wings and a white bar on the underside of their notched tail, both of which are highly visible when flying. Nighthawks lack the long, whisker-like rictal bristles of their relatives, but like other nightjars, have small bills, short legs, and large mouths. Nighthawks come in a variety of colors that vary with geographic range with our own nighthawks sporting some of the darkest plumage and fewest white markings. In zoology, there's a rule referred to as Bergmann's Rule which holds that warm-blooded animals found in the north will be larger than animals of the same species found in the south. This is an adaptation for weathering colder climates in the north. Common nighthawks are no exception to this rule and our nighthawks are moderately large when compared with their counterparts in southern regions of North America.

Nighthawk roosting on a fence post, A. Reago & C. McClerran.

During the breeding season, nighthawks can be found in a diverse array of habitats. Unlike whip-poor-wills, nighthawks will nest in open areas such as grasslands, sand dunes, agricultural areas, and recently burned forests. Interestingly enough, Common nighthawks will also nest in urban areas if the right conditions are offered - i.e. gravel roof tops and nearby trees. In many ways, large, flat gravel rooftops mimic the natural open conditions used by nesting nighthawks and have been documented as nesting sites since the 19th-century. Nearby trees are important as they support the insects nighthawks prey upon and offer roosting sites for birds not busy incubating nests. Females (who are responsible for selecting the nest site) have been documented reusing rooftop nest sites year after year. Like other nightjars, nighthawks lay their eggs directly onto the ground and no actual nest is constructed. Females incubate the eggs by day while males roost in nearby trees.

Wherever they nest, female nighthawks heavily rely on their cryptic plumage to camouflage themselves and their young at their exposed nest sites. Incubating or brooding adults will often remain motionless until the very last possible moment to avoid detection. When a potential predator approaches too closely, both males and females will defend their eggs or nestlings. Males will divebomb and boom towards intruders (like the one that boomed over my head in barrens). Females will often employ a distraction display in which they feign an injury and try to lead would-be predators away from the nest. While defending the nest, females may even give a threatening hiss while showing off their large mouths. Nest predators include owls, foxes, coyotes, skunks, raccoons, and even deer. Free-ranging pets such as cats and dogs also pose serious threats to both adult and young nighthawks. Consequently, keeping our pets indoors, in outdoor enclosures, and on leashes represent an easy way to help protect nighthawks (and many other birds) during this important and vulnerable period of their lives.

A nesting Common nighthawk, B. Garrett.

The Common nighthawk is the most widespread nightjar in all of North America. Its northern breeding range spans from southern Newfoundland west to the Yukon Territory. Nighthawks breed in every state in the U.S. and can be found nesting in interior sections of Central America.

Although booming nighthawks should surely be sought out in the summer months, the migration of this species is a spectacle to behold. They are one of the last species to arrive to their northern breeding grounds each spring and one of the first species to depart for South America. Their flights, spanning from Northern Canada to Northern Argentina, are some of the longest-distance migration flights among American birds. In rare events, vagrant nighthawks have turned up across the Atlantic in the British Isles. Although territorial in the breeding season, nighthawks are gregarious during the migratory period. Their migration flights are conducted en masse with groups of dozen, hundreds, and even thousands of nighthawks flying south together. These flights can take place day or night and, when noticed, can be hard to look away from. I can remember sitting out on the grass one August evening and listening to an outdoor concert when suddenly the sky was alive with nighthawks bounding out the northeast. I was so mesmerized, I lost all awareness of the concert and found my eyes trailing skyward for one last look at these spectacular birds as they depart for another year.

Nighthawk migration, R. Galvez.

Like so many other aerial insect-eating birds, the Common nighthawk is undergoing a widespread decline. Among aerial insectivores, nightjars are suffering some of the most pronounced population declines. As with many nightjar species, illuminating the factors directly responsible is a challenge, in part, because this species is so difficult to observe directly. We can hypothesize about some likely contributors, however. As previously mentioned, nesting nighthawks are vulnerable to introduced predators such as cats and dogs. Although somewhat more tolerant of development than other nightjars, the destruction of suitable habitat is also likely contributing to losses of these birds. The conversion of roofs from gravel to rubber is likely to lead to losses of nighthawks in urban areas. We also know that, as animals that depend solely on insects for food, nighthawks are vulnerable to declining insect populations. Recent studies have revealed what anecdotal evidence has suggested for decades: insect populations are plummeting. Healthy insect populations are an essential part of our world's ecosystems. Loss of habitat, pesticide pollution, and the changing climate have all been incriminated as key drivers of their loss. Fortunately, as some of the most widespread and numerous of nightjars, nighthawks are somewhat more resilient to these stressors when compared to the less common Eastern whip-poor-will.

It is more important now than ever to document the status of our nighthawks so that we can help them weather this volatile period and work to address drivers of their decline. Doing so will help to ensure that future generations have the chance to experience the wonder of witnessing nighthawk migration and get to spend warm summer evenings out listening for booming nighthawks. The Maine Nightjar Monitoring project needs additional volunteers to adopt monitoring routes throughout the state and help gather observations of nighthawks during the breeding season. Each year, our volunteer nightjar monitors set out on calm summer nights to conduct sunset surveys (for nighthawks) and moonrise surveys for whip-poor-wills. Many routes are still available and can be viewed on our Routes page. To volunteer, visit the volunteer signup page and join our effort to study these fascinating birds. Nightjar monitoring is as rewarding as it enjoyable. If you are new to birding or still learning to recognize birds by ear, we have many resources for improving your ID skills. Check out the bird profiles on The Birds We Study page to learn more. We hope you will take part in our effort and take this chance to get to know some of Maine's most charismatic bird species.