The Many-Tongued Mimic

close-up of a mockingbird's head with an insect in its bill
northern mockingbird portrait by Veit (CC BY-ND 2.0)

Every winter we have at least one unusual bird visitor. The winter before last it was the northern shrike. Last winter, during the pandemic, most birders were excited about the superflight south of boreal birds and welcomed huge numbers of pine siskins, red-breasted nuthatches and common redpolls, as well as evening grosbeaks and even hoary redpolls at their feeders. We saw only an occasional pine siskin with a flock of American goldfinches.

Instead, we were surprised by the appearance of a northern mockingbird on November 10 during a long period of Indian summer weather.

While northern mockingbirds are common yard birds in much of Pennsylvania, we had, up until 2020, only five detections of these birds on our mountain, and they had been in the spring. But our son, Mark, who was living in our guesthouse with his wife Paola and his brother, Dave, at the time, described the November mocker as a skulker that would appear around six in the morning and move quickly from its shelter in the huge old barberry hedge that stretches several hundred feet from the guesthouse to the shed, up to a lilac shrub near our veranda and then on to large forsythia bushes near our garage.

Mark continued to see the mocker every morning, but I didn’t have my first sighting until a cold day late in November as I headed across First Field. In the middle of the field, perched in a large, native, black haw shrub with four American tree sparrows, was the northern mockingbird. I had a good, long look at her mostly gray body with whitish breast and belly, white wing bars, and, when she finally flew, a flash of black and white tail feathers.

mockingbird sitting on a branch with red berries
female northern mockingbird by Lucina M (CC BY-NC 2.0)

I decided she was a female because she never sang but merely “chipped” a few times at dawn. Female mockingbirds sing quietly only during nesting time, but males sing most of the year. Furthermore, according to K.C. Derrickson, who studied mockingbirds in southeastern Pennsylvania and Maryland, many females in Pennsylvania establish their own winter territories in November apart from their mates, based on the available fruit, cultivated or wild, in an area, especially multiflora rosehips. Although we had a few of the latter around the perimeter of First Field, we had a lot more barberry, mile-a-minute and even an old apple tree with apples still clinging to it.

My husband, Bruce, had the next sighting on a bitter cold afternoon in early December when she landed briefly on a hackberry tree outside the sunroom. Three days later, on December 10, I saw her again, this time alone, in the black haw shrub. She sat still as I crept closer and closer. Then she spread her black and white tail before flying across the field toward the barberry shrubs at the edge of Margaret’s Woods.

Northern mockingbirds prefer early successional habitat at low elevation (less than 1,300 feet), and Mark established that they had territories at the base of our mountain on the Sinking Valley side. This rural area with brushy pasture and agricultural fields bordered by dense shrubs along with the mowed lawns and shrubs of suburban homes is ideal mocker habitat, and we thought that “our” mocker had followed the powerline right-of-way that crosses the valley up to our property.

hunched-up mockingbird sitting on a bare branch
mockingbird wintering in southern Vermont by Putneypics (CC BY-NC 2.0)

She made her appearance again during our Christmas Bird Count on December 20, and Dave saw her on a tree branch near his front porch on December 27.

Dave has had a Twitter account and blog for over a decade that he calls The Morning Porch, where he recorded her sitting in a bush beside our stream and chasing off other birds that tried to drink there on January 5. Mockingbirds are known to be aggressive toward their own species and other bird species too throughout the year.

The following day Bruce saw her land on our large bird feeder hanging on our back porch, but mockers are not usually feeder birds unless there is fruit or suet in feeder areas, neither of which we had.

On January 8 I had my best and, as it turned out, my last view of her. I had followed a deer trail through the dried goldenrod of First Field to the back of the barberry hedge. I pished and out from its depths popped the mockingbird. She sat on a hedge branch for a minute or so and then flew to the old apple tree below the hedge, where she poked at a few wizened apples and ate a little before flying away.

a mockingbird eating a crabapple by Stan Lup (CC BY-NC-ND 2.0)

Dave had three more reports on his Morning Porch. The first was on January 12 when a mixed flock of winter birds flitted through the yard and the mockingbird flew over the guesthouse and peacefully joined them at a half-frozen seep.

On January 22 he wrote, “Half an hour before sunrise, the first inquisitive ‘chirps,’ mockingbird,” and finally on January 27, “Is it night or day? The 7 o’clock factory whistle [in our town] has the answer. Two minutes later the mockingbird begins to chirp—that take-charge tone.”

We can only hope she returned to the valley because after that came days of snow and cold that blanketed our mountain with more than a foot of snow and ice that lasted throughout February.

singing mockingbird by Stan Lupo (CC BY-NC-ND 2.0)

A member of the Mimidae family, the Latin name of the northern mockingbird is Mimus polyglottos roughly translated as “many-tongued mimic.” Mockingbirds, as a whole, don’t only mimic the sounds and calls of at least 200 songbirds but also a wide variety of natural and human-made sounds. For instance, one mockingbird at Boston’s Arnold Arboretum mimicked 39 birdsongs, 50 bird calls, and a frog and cricket, and the average number of song types of four males in southeastern Pennsylvania was 148 in 1980 and 167 in 1981.

Mockingbirds sing all day and sometimes all night especially if they are unmated males, beginning in February through most of November. Mockers also may have a different slate of songs for fall and spring and are known as open-ended learners, like parrots and European starlings, meaning that they continue to learn new songs throughout their lives. They sit and sing on top of shrubs, fences, trees, utility lines and poles and walk, hop, or run on the ground with their tails cocked up. The male’s singing is thought to be both a way to attract and stimulate his mate and to defend his territory from other male mockingbirds.

two brown-speckled blue eggs in a nest
eggs of a northern mockingbird in Texas by Rich Mooney (CC BY-NC-ND 2.0)

Males will fight over territory boundaries by first flying toward each other, landing near the boundary and silently hopping from one side to another. When this approach doesn’t work, they may fly at each other and grab with their wings and claws and peck. While males keep off males, females keep away other females.

Northern mockingbirds are mostly monogamous and some pairs stay together for life. In Pennsylvania Derrickson followed one pair for six years. In addition to singing, a male mockingbird attracts a female by building the outer twig foundation of several nests in shrubs and trees three to 10 feet from the ground. She then chooses one of those nests and lines the cup-shaped nest with grasses, rootlets, leaves and even such trash as dental floss, laundry lint, bandages, duct tape, pieces of plastic and aluminum foil.

In southeastern Pennsylvania, a female mockingbird begins laying her three to four pale blue or greenish-white eggs spotted with red or brown in mid-April and incubates them for 12 to 14 days. The male perches on a high point nearby and guards her, the eggs, and later the nestlings from predators such as blue jays, fish and American crows, red-tailed hawks, snakes, squirrels, raccoons, opossums, cats and even humans by chasing them away from the nest. Sometimes as many as six mockingbird neighbors will join together to mob and chase away possible nest predators.

The nestlings are born naked, blind, and covered with light down. Both parents feed them 82% arthropods and 18% fruit. The nestlings fledge fully feathered at 12 days of age and can fly well when they are 20 days old. The parents feed them for three weeks more, but the male often takes complete charge if the female starts refurbishing another nest and laying eggs for a second brood.

four baby birds in a nest, two with mouths agape
mockingbird chicks in Florida by Jim Mullhaupt (CC BY-NC-ND 2.0)

Immatures never breed on their natal territory and can disperse up to 200 miles which may be how what used to be mainly a bird of the southern United States in the early nineteenth century has become a bird that nests as far north as southern Canada.

In Pennsylvania mockingbirds have been moving northward since the 1950s, although avoiding densely forested areas across the northern tier. They are still most common in southeastern Pennsylvania but are also plentiful in the Ridge-and-Valley Province and in southwestern Pennsylvania including the Pittsburgh Low Plateau. Altogether, the state has an estimated 200,000 singing males so we should have no trouble hearing even more of the mockingbirds in years to come.

a mockingbird in flight
an over-wintering mockingbird in Vermont takes flight by Putneypics (CC BY-NC 2.0)

Fishy Crows

Fish crows at Great Meadows NWR, Concord, MA. Photo by Tom Murray (CC BY-NC 2.0)

“Listen. Those birds don’t sound like crows,” my husband Bruce said, “but they look like crows.”

He pointed to blackbirds perched on the light poles and flying above Wegman’s parking lot in State College.

They sounded as if they were American crows with colds in their noses, a nasal “eh-uh.” But they looked like American crows.

Later, I learned they were fish crows and that they had slightly smaller bodies, more tapered wings, faster wingbeats, and shorter legs than American crows. Such differences are almost impossible to note in the field, which is why most birders can only positively identify fish crows by their unique calls. These crows live along the Atlantic and Gulf coasts from Maine to east Texas and inland along major rivers from Pennsylvania south to Mississippi.

Fish Crow from Birds of America (1827) by John James Audubon, etched by Robert Havell

Fish crows were first observed along the Delaware and Schuylkill rivers in Philadelphia by Scottish ornithologist/artist Alexander Wilson, who named them Corvus ossifragus in 1812. And ornithologist/artist John James Audubon mentioned seeing them in the 1830s along the Delaware River almost to its source. By 1903 they were nesting in small Philadelphia parks including a park across from the Academy of Natural Sciences, where the fish crows stole skeletons that taxidermists had put out to bleach on the roof.

Since then, they have moved up all our major and minor river valleys north and west including, in the last couple decades, the Ohio River drainage.

Like American crows, fish crows are opportunistic. Not only have they expanded their habitat from coastal marshes and beaches to lakes and rivers but also to farmlands, wooded neighborhoods, and suburban areas.

Their food choices are omnivorous—carrion, trash, berries and other fruits, grain, crabs, turtle eggs, and nestlings and eggs of songbirds such as blue jays, red-winged blackbirds, brown thrashers, common grackles, and northern mockingbirds and water birds including herons, gulls, ducks, plovers, rails, terns, and double-crested cormorants. They even will nest in heron colonies and raid their nests, and when they find a good source of food, they may cache it to eat later or to feed to their nestlings.

If they migrate at all, it is only to good sources of food such as landfills, feed lots, and malls and shopping centers with accessible dumpsters. They usually join winter roosts of American crows but return to their breeding grounds as early as February in Pennsylvania.

Fish crows are monogamous and have no courtship displays, although Kevin McGowan, who studied them in Florida, wrote in his Birds of the World account that he observed “a nest-building crow with stick in its bill flying slowly with stiff wings in exaggerated ‘butterfly fashion’ circling nest site completely before going to nest, repeated several times,” but whether or not that was a courtship display has not been determined. However, mated pairs do preen the back of each other’s heads.

Fish crow with nest under construction – photo by Andy Reago & Chrissy McClarren (CC BY 2.0)

Both sexes build their nest in tall trees as high as 80 feet. It takes them approximately nine days, although they start several nests before lining and finishing one. They may use the same tree sometimes for years, but they always build a new nest of deciduous tree sticks and line it with soil, red cedar, or grapevine bark, hair and/or pine needles. The finished product is 19 inches across with a cup of five inches.

Here in Pennsylvania fish crows may build a nest as early as April 11 or as late as June 29. They have a small territory around their nest tree, and occasionally they will breed semi-colonially among several other fish crow pairs with nests within 100 yards of each other. The male fish crow defends the nest site from American crows, but he will often allow other fish crows to approach his nest.

The female fish crow lays two to six pale bluish-green eggs marked with brown which she incubates while the male guards and feeds her, bringing food in his throat not his bill, both for his mate and later his nestlings.


Red-tailed hawk being mobbed by fish crows in Brooklyn – photo by Will Pollard (CC BY-ND 2.0)

Both mob possible nest predators, most notably hawks, raccoons, owls, and humans. After the eggs are incubated for 16 to 19 days, the naked, helpless young emerge and take 32 to 40 days to mature and fledge.

Fish crows have not been studied as much as American crows but like their congeners they are curious, intelligent and social birds that will play with objects they find. However, they can be aggressive toward each other, for instance, a fish crow at a garbage site was observed pulling the tail of another fish crow which then flew away.

More serious fights begin with threatening posturing, during which they arch their necks, hold their heads forward and point their bills downward, spread their tails, slightly spread their wings or keep them close to their bodies with their wing tips down, and walk sideways toward their opponent. After fights, they perform an appeasement display consisting of open-mouthed begging calls, lowering their bodies and quivering their extended wings, and they always give in to American crows in fights.

Although I can easily see and hear fish crows in State College and on the Penn State campus where they roost in the winter and breed locally, I have yet to see and hear them in my own Blair County. But other folks have because the fish crows have come by way of the Frankstown Branch of the Juniata River into our county. The first record was April 15, 2006 by Roy Boyle at the north end of Altoona.

Fish crow at Camman’s Pond, Long Island – photo by Beth Fishkind (CC BY-NC-ND

Closer to our home on Brush Mountain in northern Blair County, our son Mark heard a fish crow in Sinking Valley below our mountain in April 2015 and frequently saw them in the springs of 2016 and 2017 over the farmland between Tyrone and Bellwood and on the wetland behind the Northern Blair County Recreation Center.

The following July (2018) Mark and our other birder son Steve were sitting on our veranda when they heard a fish crow call as it flew above Sapsucker Ridge. Then from March 19 until July 14, 2020 Mark saw fish crows along the Little Juniata River at the base of our mountain. His highest number was 12 on March 19. And the most he saw fly over our farm together were six fish crows on March 31. But most days he had one or two throughout the spring, summer, and as late as October 9. Clearly they were attracted by the river.

While in Pennsylvania the highest number of fish crows are in the lower Susquehanna River valley in the counties of York, Cumberland, and Lancaster and along the lower Delaware River and its tributaries, they have greatly expanded their range from the first to the second atlasing of Pennsylvania breeding birds according to Douglas A. Gross. They are “strongly associated with pasture in Pennsylvania,” he wrote in the Second Atlas of Breeding Birds in Pennsylvania. Since they are scarcely ever above 1000 feet and rarely ever in densely forest areas, I can’t expect to see them breeding in our tall trees at 1200 feet in elevation, but they have increased 86% in the number of blocks of fish crow records from the first Atlas of Breeding Birds in Pennsylvania. Their state population is estimated to be about 30,000 and nationwide 450,000 according to Partners in Flight. Even though West Nile virus killed many in the early 2000s, their numbers have recovered. But as Gross concludes, “Although it [fish crow] has made advances, it is not nearly as common and widespread as the seemingly ubiquitous American crow.”

The Mystery of Night

Last September fall songbird migration was well underway. Almost every day I encountered a migrant in our yard, our meadow, or our forest. Many of the birds are not as colorful as the males are in spring and there are huge numbers of immature warblers that wear the drab coats of females such as the warbler I spotted as I walked up our driveway. It was foraging in a small black walnut sapling behind an old apple tree and paused long enough for me to note its grayish back and head, faint wingbars, yellow throat, breast and belly with faint streaking on its neck and breast. After studying Roger Tory Peterson’s two pages of fall warblers in his Field Guide to Birds of Eastern and Central America, I decided that the bird was an immature female prairie warbler.

An immature female prairie warbler (Photo by Linda Tanner on Flickr, Creative Commons license)

An immature female prairie warbler (Photo by Linda Tanner on Flickr, Creative Commons license)

Meanwhile, our birder son, Mark, was out every morning at dawn hiking eight miles up and down our property, recording bird species and numbers on his phone, the same as he had done during spring migration when he had found 101 species one mid-May day.

In both spring and fall, the migrant birds come into our property to eat and rest for the day because most songbird species—sparrows, warblers, flycatchers, thrushes, orioles, and cuckoos—migrate at night when they are safer from predators such as day-flying raptors, and it is also quieter.

Migrant birds use the Earth’s magnetic field to help them migrate, and recently researchers discovered how they see in the dark. A protein called cryptochrome, which is sensitive to blue light, allows them to do this because of an unusual cryptochrome eye protein birds have called CRY4.

So many birds migrate each fall that they can be detected by Doppler radar. And they are especially abundant when low weather systems are followed by highs that bring north winds.

Before they leave their breeding grounds they gorge on foods filled with carbohydrates and lipids like berries and other fruits and store them as fat. For instance, ruby-throated hummingbirds double their weight in four days before they embark on a 2,000 mile migration to Mexico and Central America. And here in Pennsylvania most ruby-throated hummingbirds are on their way as early as mid-August or early September.

A Swainson’s thrush (Photo by Mark Bonta taken in Plummer’s Hollow)

A Swainson’s thrush (Photo by Mark Bonta taken in Plummer’s Hollow)

Migratory birds sleep less, but they do sleep while flying. Swainson’s thrushes sleep for nine seconds on one side of their brain and then switch to the other side for nine seconds, keeping themselves half- awake to avoid predators or mid-air collisions with other migrating birds, researchers discovered.

In addition, migratory birds give short calls as they migrate at night, probably also to avoid colliding with other birds during massive migratory flights as well as for echolocation. Most of those calls sound nothing like their daytime calls and songs.

Back on September 14, 1896, Orin Lobby sat on a hill near Madison, Wisconsin and counted 3600 calls from night-flying birds during five hours of listening. His was the first known attempt by anyone to do this. There were only two other such studies in the next 50 years—one by Paul Howes in 1914 and the other by Stanley Ball (1952)—and both documented the night time call of thrushes, which are more distinctive than other songbird calls. Ball’s work was also the first to use such calls to time the migration of a region’s species.

The first audio recordings made of nocturnal flight calls (NFCs) used reel-to-reel tape recorders to automatically record 10-minutes out of every hour all night so recorders could sleep and later listen for bird calls on the recorders.

Then Bill Evans, in the 1980s, used commercial hi-fi video cassette recorders to record 8 to 10 hours of NFCs a night. In 1994, he joined the Cornell Lab’s Bioacoustics Research Program (BRP) working under Dr. Chris Clark to help develop computer-based automatic NFC detectors and BRP programmer Harold Mills wrote the first working NFC detector which could detect short, high-pitched flight calls of warblers and sparrows.

A wood thrush on our property (Photo by Mark Bonta)

A wood thrush on our property (Photo by Mark Bonta)

But Evans wanted to encourage citizen scientists to participate in NFC monitoring so he founded a nonprofit he called OldBird for NFC monitoring. Then he contracted a former BRP programmer, Steve Mitchell, to develop advanced software to be used on home computers. They began with dickcissel and thrush detection, but today anyone interested in listening to and recording the calls of NFCs on their home computer can purchase their own Autonomous Recording Unit and set it up.

That’s what our son, Mark, did last fall. On a pole near our barn, he attached an OldBird, 21c microphone enclosed in a large white bucket pointed skyward and ran a cable from the microphone into the barn where he had his laptop computer equipped with software to analyze bird calls.

The bucket, he explained, helped the microphone pick up calls as high as approximately 1,950 feet in the sky and within 975 feet of the microphone.

Flight Calls of Migratory Birds CD

Flight Calls of Migratory Birds CD

There is no field guide to NFCs, but there are sources online that are mostly based on Evans’s and O’Brien’s CD-Rom “Flight Calls of Migratory Birds: Eastern North America.” Mark showed me pages of NFC spectrograms and also had me listen to the short “zeeps” of several of these birds. The length of each call (in milliseconds) was at the bottom of the spectrograms and the sound—from 0 to 12 Kilohertz—on its left side. Near zero it was mostly black from insect noise, and Mark found that the din from katydids until a good freeze in mid-October made it almost impossible to hear the bird calls in September. So he did most of his recording from October 14 until November 22.

In all, he, with the help of fellow NFC experts and enthusiasts, identified 47 species. Some were easy, such as American robins that have the same call they use in the daytime, and others have distinctive spectrographs such as that of American redstarts which I identified immediately. The sparrows and warblers are all in the high kilohertz (six to 10 range) and nine warbler species have almost identical “zeep” calls lasting 60 milliseconds, while another nine warbler species with “up” calls last 30 to 50 milliseconds. But only two warbler species—northern parula and pine warblers—have the “single down sweep” calls at 50 milliseconds.

The sparrows are mostly two to a category, but Mark was able to distinguish most species. Still, even the experts are still working on 10% to 20% of bird species’ calls that can’t be identified. And he had his own mystery bird at 11:37 on November 12. No one, not even Bill Evans, is able to identify it so far.

Snow bunting flight call, detected during the early morning hours of November 13, 2020. Picked up loud and clear on a cold, insect-less night. Pitch descending from six to two kilohertz over 250 milliseconds (Image by Mark Bonta)

Snow bunting flight call, detected during the early morning hours of November 13, 2020. Picked up loud and clear on a cold, insect-less night. Pitch descending from six to two kilohertz over 250 milliseconds (Image by Mark Bonta)

On the other hand, the following night Mark heard the clear call of a snow bunting, a species we have never seen on our property. Another was that of a horned lark with the same call as we have heard down in Sinking Valley where they nest and even winter. He also recorded many savannah sparrows even though again we have never had one here.

As expected, the thrush calls were easy to distinguish and he heard gray-cheeked and Swainson’s thrushes, both of which I encountered on my walks. On September 19 a gray-cheeked thrush was foraging in the undergrowth beside Laurel Ridge Trail. A grayish, plump thrush, it has one of the longest migration routes—from the edge of the tundra to Brazil—of the thrush species and is the first thrush species to migrate, passing through Pennsylvania as early as the last week in August, although their primary time is from the second week in September to the first week in October.

The Swainson’s thrush I observed on October 4 in the underbrush beside our hollow access road. It breeds across Canada and Alaska and in the northern United States and migrates to Central and South America.

Wood thrushes and hermit thrushes both nest in Pennsylvania and wood thrushes, which are headed to Mexico and Central America for the winter, are mostly gone here by the first week in October, but hermit thrushes, the only thrush species to winter in the United States, including in Pennsylvania mostly in the southeastern part of the state, are the last to leave in mid-October to early November. Mark counted sometimes dozens of them a night.

As David Brown from Lycoming County writes on his excellent website about NFCs, [hearing] “the descent of thrushes in the pre-dawn hours of a fall is hard to beat…”

Greater yellowlegs flight call detected twice in early November 2020. Series of five notes around three kilohertz, lasting 800 milliseconds total (Image by Mark Bonta)

Greater yellowlegs flight call detected twice in early November 2020. Series of five notes around three kilohertz, lasting 800 milliseconds total (Image by Mark Bonta)

Flocks of geese, swans, and shorebirds also migrate at night and Mark recorded “tons of tundra swans,” and one night a greater yellowlegs call, a month later than any have been reported migrating. It is for such discoveries that Mark especially enjoys analyzing NFCs.

But he also likes hearing mammals moving about such as deer startling a bird or coyotes howling in the distance, what he calls the “mystery of night.”

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.

A common nighthawk flying (Photo by Kenneth Cole Schneider on Flickr, Creative Commons license)

A common nighthawk flying (Photo by Kenneth Cole Schneider on Flickr, Creative Commons license)

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.”

A common nighthawk on the ground (Photo by Kenneth Cole Schneider on Flickr, Creative Commons license)

A common nighthawk on the ground (Photo by Kenneth Cole Schneider on Flickr, Creative Commons license)

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.

A common nighthawk nest (Photo by Kenneth Cole Schneider on Flickr, Creative Commons license)

A common nighthawk nest (Photo by Kenneth Cole Schneider on Flickr, Creative Commons license)

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.

Nighthawk courtship flight, illustrated by Alexander Wilson in 1829

Nighthawk courtship flight, illustrated by Alexander Wilson in 1829

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.

Common nighthawk young in their nest (Photo by Clinton & Charles Roberts on Flickr, Creative Commons license)

Common nighthawk young in their nest (Photo by Clinton & Charles Roberts on Flickr, Creative Commons license)

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.