Links to some of the sources used for the story:
Gretchen Newberry, University of South Dakota, Vermillion
Species at Risk, Canada
Cornell Lab of Ornithology Common Nighthawk
Laura's Conservation Blog APA Bird of the Year
Partners in Flight Saving our Shared Birds
Common Nighthawk Population Decline in the Seven County Metropolitan Region Results of the 2001 statewide (Minnesota) volunteer nighthawk survey (page 3 of The Loon, Spring 2002)
By Molly McGuire
In this issue we look at the common nighthawk, a bird now less-than-common, in steep decline. You can order the issue here, or subscribe, or call us at 800-303-8201 for information on receiving a digital subscription.
Where have all the nighthawks gone? A few years ago their squawk and roar were part of the summer evening soundtrack of midwestern river towns, especially downtown near the river.
The ironically named common nighthawk is neither hawk nor specifically night flying, and now it’s not all that common. Many of us remember these dark pointy-winged birds zig-zagging between old downtown buildings, scooping up moths, mosquitoes, mayflies and other insects that fill the warm summer dusk, their cries echoing off the buildings. According to The Birds of North America (Cornell Lab of Ornithology), nighthawks exploit water sources, and Mississippi River bugs offer a nice buffet.
The common nighthawk (Chordeiles minor), sometimes known as the bull-bat, is in the nightjar family, which also includes whip-poor-wills. The nightjars generally nest on the ground and have short legs and bills and long pointed wings.
Nesting on flat, gravelly ground or rocky areas in the wild, a nighthawk’s nest usually just involves laying a couple camouflaged eggs in an indentation. They also learned to nest on gravel-covered flat downtown rooftops around the country, as natural areas diminished. The rooftop nests have the advantage of being out of the reach of terrestrial predators.
This neotropical migrant flies one of the longest migration routes of any North American bird, from Canada and the United States deep into South America. Flocks of migrating nighthawks are still seen in Duluth, coming down from Canada, and along the migration route along the East Coast. Usually, however, during nesting season, birders report seeing only one or two, or maybe a small group.
Aerial insectivores, especially those with long-distance migrations, have taken a heavy hit. Others in this category are the chimney swift, purple martin and several swallows. The State of the Birds 2014 report classifies nighthawks as common, but in steep decline. A species makes this ominous list if its population has declined at least 50 percent since the mid-1960s, based on breeding-bird surveys and other counts. In Canada, the nighthawk is protected under the Species at Risk act. Data from 1968 to 2005 points to an overall decline of 80 percent. Estimates put its decline in the U.S. at 59 percent.
Counting nighthawks is difficult. Many counts are done during the day, but nighthawks are quiet unless hunting in the air, mainly at dusk and dawn. Their markings make them almost invisible when they roost. They have short, weak legs and actually sit on a branch sideways. It’s possible to sit down next to a resting nighthawk on a rock ledge or stone wall and not know it is there. (Once I was alarmed when I saw an eye blink in an odd-looking pile of leaves.) Both males and females will feign an injured wing and try to lure predators away when their nest is threatened.
There are many untested theories to explain their decline. Use and overuse of insecticides in both North and South America may be affecting their health and food supply. Gravel roofs have largely been replaced by plastic-coated ones, which become meltingly hot and offer no camouflage from predation by crows, which have become more populous in urban areas. Efforts to attract nesting nighthawks to roof-top gravel boxes have not shown much success.
It will be difficult to restore nighthawk populations without understanding exactly why they are in decline.
Laurence Gillette and Carol Carter reported on a nighthawk survey in 2001 that recorded a steep drop in the seven-county Twin Cities area since the previous survey in 1991. Gillette believes that the numbers were so low that another survey would be difficult.
Gretchen Newberry, who studies nighthawks at the University of South Dakota in Vermillion, has designed a survey that will count the birds at dusk and dawn, when they are most active, as opposed to other bird surveys conducted during the day, or at night, like the National Nightjar Survey.
According to Newberry, common nighthawks are abundant only in a patchwork of grasslands that have not been farmed. Numbers may have increased when they started nesting on flat roofs, but she wonders if urban nighthawks stumbled into an ecological trap, as roofing materials changed and became unsuitable for nesting. She does not assume that they will find their way back to natural nesting areas, or if there are enough of these areas to sustain a sizable population.
Although nighthawks prefer open grassy areas, she has seen some sparse nesting on sand bars. They will forage for insects along small tributaries and roost on big cottonwood trees during the day near rivers in riparian areas.
Because nighthawks migrate in huge flocks, Duluth is still a popular place to see a bunch of nighthawks swooping in the sky. Although the numbers now are believed to be far lower than in the past, watchers in late August have seen thousands flying south on their way to South America. Laurence Gillette does not see as many migrating as he used to.
Common nighthawks are endangered in Vermont, New Hampshire and Connecticut; of special concern in Indiana, New Jersey and New York; and on the watch list in Maryland. Gretchen Newberry believes that nighthawks will not be put on the federal endangered list, because the law is written to favor species that are in peril in smaller areas.
A research paper in 2010 studied declines in aerial insectivores and found that birds with long migration routes — such as Canada to South America — showed an acute drop in the mid-1980s, higher than birds that flew to Central America. Researchers theorized that this drop was due mostly to pesticides, including some in Central and South America that are not used in North America. These affect not only the flying insect prey of the nighthawk, but also possibly bird reproduction. They speculate that because long-flyers have more energy demands than their short-distance cousins, they are suffer more when their habitat and food is degraded.
The report cites an earlier study that looks at how common species can decline and still show up on grid-based surveys, making initial declines in a common species much less noticeable than later declines.
I'm afraid we will continue to notice the absence of these twilight dive-bombers.