Bird Brains

Don’t call anyone a bird brain unless you are complimenting them. In the last couple decades, researchers worldwide have been discovering how amazing bird brains are. That should not be a surprise since feathered winged animals that fly have been evolving on earth for more than 150 million years, according to recent genetic analyses.

Neuroscientists Suzana Herculano-Houzel and Pavel Nemec recently published a paper entitled “Birds have Primate-like Numbers of Neurons in the Forebrain,” in which they write that the brains of birds are organized much like those of primates.

“We found that birds, especially songbirds and parrots, have surprisingly large neurons in their pallium: the part of the brain that corresponds to [our] cerebral cortex, which supports higher cognition functions such as planning for the future or finding patterns.”

To truly understand how intelligent birds are, researchers study how a species behaves in the wild, conduct experiments with captive birds, and compare what they see in the field with what they learn in the lab about a species’ genes and cells.

Some bird species seem to learn as little as possible to get along. Others are bird Einsteins. Most are in between. But relatively few of the more than 9000 species of birds worldwide have been studied in detail. And in much of the last century, even though people had been reporting anecdotally what appeared to be the intelligent actions of some birds such as crows and ravens, scientists had not begun any systematic studies of birds’ brains.

An American crow on a fence post

An American crow on a fence post (Photo by Joe McKenna on Flickr, Creative Commons license)

While some of us have watched parrots dance to music and New Caledonian crows solve problems on You Tube, many of our common birds are just as clever. American crows, for example, are adept at problem-solving. One researcher observed an American crow carrying water in a Frisbee to dampen its dried mash and another one using the end of a plastic slinky toy to scratch its head while it was perching.

According to research by John Marzluff in Washington State, American crows can recognize human faces, using the same parts of their brains to do this as we do. They plan ahead when they find and then leave a gift for a human who has been feeding them. In addition, they will delay gratification if they think they will be offered something better (usually food) at a later time.

Common ravens are socially adept, remembering other ravens they were friendly with before they paired for life, recalling those special friends even after they have been separated for three years.

A blue jay with an acorn

A blue jay with an acorn (Photo by Jeff Hart on Flickr, Creative Commons license)

Still another member of the Corvid family, our blue jays, can accurately select fertile acorns 88% of the time and can count to five. They also mimic red-shouldered and red-tailed hawks. Blue jays often mimic the latter on our mountain and fool us. Some scientists hypothesize that they do this to trick other blue jays into thinking that there’s a raptor in the area and they need to leave, giving the blue jay imitating the red-tail time to harvest acorns without competition.

Another scientist noticed that a blue jay was smart enough to rub red ants on its body to get rid of the ants’ formic acid before eating them.

Because more than 80% of bird species are socially monogamous, staying with one partner for a season or even, in some cases, for life, they have developed “relationship intelligence,” which is an ability to understand what their partners want or need and respond in order to successfully breed and raise their young.

But apparently 90% of both sexes also sneak off to copulate with others without getting caught by their partners. This results in more healthy offspring.

In autumn, birds that store food for the winter, such as black-capped chickadees, grow new cells in their brain center (the hippocampus) which deals with spatial memory. This allows them to remember where they hid seeds months later.

A brown-headed cowbird female in Codorus State Park

A brown-headed cowbird female in Codorus State Park, near Hanover, Pennsylvania (Photo by Henry T. McLin on Flickr, Creative Commons license)

Brood parasites such as brown-headed cowbirds, especially the females, have large hippocampuses, because they are the ones that must lay their eggs in other species’ nests. They must find, remember, and revisit the nests they parasitize.

And invasive bird species, such as house sparrows and European starlings, have larger brains, are innovative, and have more flexible behavior because they must adapt to a foreign environment.

But our brainiest birds may be hummingbirds, because their brain is the largest brain relative to its size, a whopping 4.2% of their total body weight. Their hippocampus is five times larger than that of songbirds, seabirds and woodpeckers. They can remember every flower in their territory and how long it takes them to refill with nectar after they feed from them.

A ruby-throated hummingbird at a feeder

A ruby-throated hummingbird at a feeder (Photo by likeaduck on Flickr, Creative Commons license)

From year to year at home and in migration they also remember where every feeder is. They even learn which feeder people are responsible or irresponsible and have huge episodic memories that allow them to plan when and where to feed on hundreds of flowers a day.

The females watch older females making nests to learn how to do this because female hummers are on their own once they have bred. They must build their nests, brood their eggs, and feed their young alone.

Hummingbirds have the ability to move backwards, forwards, and sideways because they have more complex brains. In the part of their brain that responds to visual stimuli, instead of the usual back-to-front preference most animals and humans have, hummingbirds have no preference and can move in any direction.

A ruby-throated hummingbird at a flower

A ruby-throated hummingbird at a flower (Photo by chrisdupe on Flickr, Creative Commons license)

During their mating flights, which we’ve watched with awe from our front porch, they make instantaneous course corrections much faster than a fighter jet. Thus, their brains can move efficiently in three dimensions, which some scientists believe makes their tiny brains the most complicated of any vertebrate species.

Hummingbirds have not been considered songbirds, but biologists Claudio Mello and Erich Jarvis have found that hummingbirds have the same areas in their brains that control song learning and production as songbirds and parrots. They do sing in a higher pitch than songbirds, but their songs are amazingly rich, and in some species, complex.

Neurobiologists have been comparing birdsong with human speech and language. Like human children, young birds listen to other birds of their species to learn songs. They imitate and practice, seemingly using the same brain structures and genes to learn songs as children use to learn language. Some birds even stutter.

There is incredible variety in birdsong, as various as the 4,000 songbirds on our planet. And if you listen as carefully as Donald Kroodsma, who has been studying birdsong, especially in the eastern United States, for more than 40 years, you might be able to hear the 30 to 40 songs of a Carolina wren, the 50 to 100 of an eastern bluebird, the song and mimicking calls of a white-eyed vireo, the 30 to 40 songs of the ethereal wood thrush, the 200 to 400 different mimicking songs and calls of a gray catbird, the 100 songs of a northern mockingbird, and the 2,000 of the mimic champion—the brown thrasher.

Then there is the hermit thrush whose song has been compared to human musical scales with trills and slides reminiscent of a woodwind instrument. Some ornithologists have claimed that hermit thrushes sing major, minor and pentatonic (five note) scales.

But composer Emily Doolittle and biologist Tecumseh Fitch didn’t believe it. Still, using recordings of 14 hermit thrushes from the Borror Laboratory at Ohio State University, they started analyzing the pitches of 114 song types. When they slowed them down, they could hear their harmonies.

A hermit thrush singing

A hermit thrush singing (Photo by Yankech gary on Flickr, Creative Commons license)

“They jumped out at us,” Doolittle said, adding that 70% of the hermit thrushes’ songs were harmonic.

And maybe most miraculous of all to us are our songbirds that migrate. Scientists have found that at first they rely on genetic information for both direction and distance until they gain experience. Then they use their own brain maps to find their way. They build up magnetic maps during migration and some may use odor to help guide them. Some researchers even think they may hear a landscape infrasonically, especially the ocean, to help navigate. But to do all that and more they must possess fantastic spatial memories.

Every day, it seems, more is being revealed about the brains of birds. It’s a hot topic. For instance, researchers have recently found that the bird that is closest to its dinosaur ancestors is our own wild turkey. That’s because, since the days of feathered dinosaurs, the wild turkey’s chromosomes have had fewer changes than those of other birds. And, as any hunter knows, wild turkeys are wily and smart.


Winter Hawks

It’s October and folks are perched on mountaintops throughout Pennsylvania watching the raptors parade south. Even on our mountain, I can sit for hours on a breezy October day and count dozens of raptors flying past.

A red-shouldered hawk in flight

A red-shouldered hawk in flight (Photo by Gouldingken in Wikipedia, Creative Commons license)

Officially, fall raptor-watching begins in mid- August and doesn’t end until mid-December, but the largest numbers and diversity of species usually occur in October on our westernmost ridge in Pennsylvania’s Ridge-and-Valley Province.

Sharp-shinned and red-tailed hawks are the most common and numerous raptors here and on other hawk watches as well in October, but there are also plenty of Cooper’s hawks, American kestrels, ospreys, northern harriers and even a few bald and golden eagles then.

A red-shouldered hawk hunting

A red-shouldered hawk hunting (Photo by Camron Flanders on Flickr, Creative Commons license)

But here and there among the red-tailed hawks, I occasionally see its smaller congener Buteo lineatus, more commonly known as the red-shouldered hawk, soaring or flapping on its own as it too heads south, mostly to the southeastern United States, to spend its winter.

Even at Hawk Mountain Sanctuary, where folks are counting raptors throughout the season, they average twice as many red-tails (603) as red-shoulders (306) most years, and peak migration for red-shoulders are the last two weeks in October at many hawk watches statewide.

This is a beautiful hawk as I learned on March 8, 2015. On our way to see short-eared owls near Gettysburg, we stopped at Lake Kay in Fairfield to look at waterfowl. Perched on a nearby powerline along a back road was a red-shouldered hawk. It was absolutely still as it peered down on the roadside in search of prey.

A red-shouldered hawk looking down from cables directly overhead

A red-shouldered hawk looking down from cables directly overhead (Photo by Richard J. Kinch on Wikipedia, Creative Commons license)

It paid us no attention as we quietly exited the car for a closer look, first through our scope and then, as we crept nearer, our binoculars, and finally our naked eyes. I was thrilled to see close-up a bird I mostly have seen flying past or once, in late April, circling low over First Field and flaring its handsome, black-and-white striped tail. But on that March day, I had an eye-popping view of its rufous upper wing “shoulders,” hence its common name, and rufous breast and belly, the latter with light barring.

I wondered if the adult bird had spent the winter there in Adams County or if it had returned, as many do, in early March. However, it was nicknamed the “winter hawk” years ago because it often winters as far north as New England, and here in Pennsylvania it has been an occasional winter resident, preferring open lowland areas in the southeast and northwest areas of the state.

According to recent Winter Raptor Surveys, red-shoulder numbers have been increasing, reaching a high of 101 in 2014, since the 2001 beginning of this annual survey. Furthermore, most wintering red-shoulders appear to be in the south-central and northwest counties. In a paper Greg Grove and Nick Bolgiano wrote for Pennsylvania Birds back in 2013, they point out that both Christmas Bird Count and Winter Raptor Survey data “suggest that the number of wintering Red-shouldered Hawks has increased in Pennsylvania during the past decade.”

A red-shouldered hawk perched in a pine tree, Nov. 28, 2015

A red-shouldered hawk perched in a pine tree, Nov. 28, 2015 (Photo by Kelly in Flickr, Creative Commons license)

The Second Atlas of Breeding Birds in Pennsylvania shows that red-shoulders also nest in many of those wintering counties, and Grove and Bolgiano suggest that some of those birds stay on their territories year round. Adams County is on the top ten wintering counties list, so the red-shoulder we saw may have been a year-round resident.

Although red-shoulders prefer lowland mature mixed deciduous forests interspersed with marshes and swamps as well as forested valleys in the mountains for breeding, they occasionally adapt to old suburban areas with large trees and water.

Red-shouldered hawks mating

Red-shouldered hawks mating (Photo by Bill Majoros in Flickr, Creative Commons license)

Red-shoulders appear to use the same nesting territory every year and even to reuse their old nest or build a new one in the same area. Returning to Pennsylvania by early to mid-March, these monogamous raptors are already paired. However, they engage in courtship displays, both the so-called “circling flight” and “sky-dancing” between 11:00 a.m. and 1:00 p.m. for about 18 days. Usually after “sky-dancing” they mate.

During courtship, they also establish and defend their 225 to 500-acre territory and work on their nests. Those nests are primarily in deciduous trees that are larger than others in the same area and are more than halfway up in the crotch of the main tree trunk. Usually, their nests are near water and are built by both parents. They use bark strips, dead and live twigs, dried leaves, lichens and live evergreen sprigs. If they are constructing a new nest, it can take four to five weeks but they can refurbish an old nest in a week.

A red-shouldered hawk on a nest

A red-shouldered hawk on a nest (Photo by Bill Majoros on Flickr, Creative Commons license)

An average of two to four dull white eggs with an “endless variety of types and colors of marking,” are laid, ornithologist Arthur Cleveland Bent once wrote. In Pennsylvania this happens in April or May. Both sexes incubate them, beginning before the clutch is complete. Because the female has a large incubation patch and the male little or none, she incubates most of the time, and the male brings in food for her.

It takes 28 days for the eggs to hatch and the nestlings emerge covered in light brown down with wide open eyes. They grow rapidly and by two weeks of age, they stand up, lie down, and flap their wings. At six to eight weeks they can climb on branches nearby and fledge which occurs in Pennsylvania in June and July. Still, the parents continue to feed their offspring for another six to eight weeks before they are on their own.

Red-shouldered hawk chicks in a nest

Red-shouldered hawk chicks in a nest (Photo by Bill Majoros on Flickr Creative Commons license)

The primary foods for both adults and young red-shoulders in the northeast United States are eastern chipmunks, mice, voles, and shrews. Other mammals include rabbits, muskrats, opossums and skunks. But they also prey on frogs, fish, toads, snakes and crayfish, hence their preference for riparian areas.

Back in 1890 in Pennsylvania, ornithologist B.H. Warren examined the stomach remains of 57 dead red-shoulders and discovered that 43 contained meadow voles, a few other small mammals, grasshoppers and other insects (mostly beetles). Nine others had frogs and insects, two had snakes and frogs, and two others small birds, small mammals, and a few beetles. None had poultry even though they were also called “hen hawks.”

A red-shouldered hawk carrying a squirrel to its young

A red-shouldered hawk carrying a squirrel to its young (Photo by Andrea Westmoreland on Flickr, Creative Commons license)

They have their own predators. Great horned owls and red-tailed hawks may take over both red-shoulders’ occupied or empty nests. They also, along with raccoons, peregrine falcons, and fishers, may kill nesting adult red-shoulders, their eggs or young.

Even though their nests are well-hidden from our eyes, as we discovered one April when we were at Yellow Creek State Park in search of waterfowl, we entered a section of woods near the water to be met by the loud “kee-aah” cries of a red-shoulder that went on and on. We never did see it despite straining our eyes and tramping through the entire area.

A red-shouldered hawk feeding its baby

A red-shouldered hawk feeding its baby (Photo by Bill Majoros on Flickr, Creative Commons license)

Red-shoulder populations seem stable now, according to a 2008 continent-wide study during autumn migration counts, although they have not attained, here in Pennsylvania, their pre-DDT numbers, probably due to the loss of riparian habitat and large blocks of contiguous mature forests. Furthermore, the breaking up of these forests into small blocks favors their primary predators, the larger and more aggressive great horned owls and red-tailed hawks. Still, between the first and second atlas of breeding birds in Pennsylvania, red-shoulder numbers increased by 55 % and Breeding Bird Surveys in the commonwealth estimated a 3.6% increase per year.

Nevertheless, red-shoulders remain a species of Maintenance Concern in Pennsylvania’s Wildlife Action Plan because of their reliance on habitat that continues to disappear particularly in northwestern and north-central Pennsylvania, areas that have remained breeding hot spots for these still understudied magnificent raptors.


Songbird Journeys

For those of us who appreciate songbirds, September is the saddest month. That’s when most of them start their long journeys south. Gone are the songs of spring and early summer, the raising of youngsters, even, in some cases, their bright spring colors.

A yellow-rumped warbler in winter plumage photographed at the Wakodahatchee Wetlands, South Florida, Feb. 7, 2016

A yellow-rumped warbler in winter plumage photographed at the Wakodahatchee Wetlands, South Florida, Feb. 7, 2016 (Photo by Don Burkett on Flickr, Creative Commons license)

A few songbirds, such as eastern towhees and yellow-rumped warblers, migrate no farther than the southern United States. Others head for Mexico and Central America. Still others spend their winters in the Amazon basin—Peru, Brazil, Venezuela, Ecuador—of South America.

Despite a century or more of migration studies by ornithologists and citizen scientists, using bird-banding, radar images, and even small airplanes, as well as on the ground field work both here and on the wintering grounds, much more research needs to be done, especially here late in the summer, when most songbirds moult, during their fall migration, and on their wintering grounds.

Recently, Bridget Stutchbury and her team at the Hemlock Hill Biological Research Area in northwest Crawford County have pioneered the use of geolocators to track long-distant songbird migrations of purple martins and wood thrushes.

A Kirtland’s warbler with a geolocator mounted on its rump

A Kirtland’s warbler with a geolocator mounted on its rump (Photo by Dan Elbert/USFWS on Flickr, Creative Commons license)

Weighing a mere 1.5 grams—that of a dime—a geolocator is carried on a bird like a backpack and is looped around the bird’s legs. Because a geolocator can detect light levels, it is able to show the cycles of sunrise and sunset so that during good weather, a bird’s geographical location can be calculated by the timing of sunrise and sunset in that area.

Working with the Purple Martin Conservation Association’s main colony in Edinboro, Pennsylvania in the summer of 2007, Stutchbury and her associates spent two mornings attaching geolocators to the birds. The martins seemed undisturbed by their “backpacks” and continued feeding and raising their offspring.

On August 31 one of the female martins flew south on the way to her Brazilian wintering grounds. In five days she made it across the Gulf of Mexico to Mexico’s Yucatan peninsula—1,440 miles. By the 13th of October, she had arrived at Manaus, Brazil and spent the winter in the Amazonian rainforest. She left Brazil on April 12 and was back in Edinboro at her breeding colony on 25th of April flying 4,200 miles in 13 days.

A purple martin taken at the Horicon National Wildlife Refuge, Wisconsin, June 28, 2009

A purple martin taken at the Horicon National Wildlife Refuge, Wisconsin, June 28, 2009 (Photo by Dori in Wikimedia, Creative Commons license)

Five days later Emily Pifer of the Purple Martin Conservation Association found that female with her geolocator still attached and, as Stutchbury wrote in her book The Bird Detective, “Emily was looking at the first migratory songbird, anywhere in the world, for whom we would know its arrival time on the wintering grounds, where it had spent the winter, and how quickly it had come home.”

Later a second female martin arrived with her geolocator and the following year three more were recovered. All indicated the same fast flight over the Gulf of Mexico from northwest Pennsylvania and similar arrival times in Brazil, in which they took more than a month migrating through Central and northern South America.

But all five of their martins averaged 23 days from Brazil to Pennsylvania in the spring, flying about 180 miles a day, thus proving that spring migration is faster than fall’s, most likely because the birds are eager to claim breeding territories and mates.

A wood thrush on its breeding ground in Chester County, PA, June 20, 2010

A wood thrush on its breeding ground in Chester County, PA, June 20, 2010 (Photo by Kelly Colgan Azar on Flickr, Creative Commons license)

Stutchbury also put geolocators on 47 adult wood thrushes in 2007 and 2008 because their numbers are declining probably due to deforestation both on their breeding and wintering grounds. In two years, they retrieved 14 wood thrushes with geolocators. They learned from them that wood thrush fall migration, mostly to Honduras and Nicaragua, is relatively slow and the arrival time varied from mid-October to early December. They too mostly crossed the Gulf of Mexico, especially in the spring when they flew on average 2,160 miles in two weeks.

However, one female did not cross the Gulf, and instead she flew an extra 600 miles overland, arriving much later on her nesting grounds. Why she did this is anyone’s guess, although Stutchbury wondered if she had left her wintering territory in poor condition and hadn’t the strength to cross the Gulf.

Stutchbury further questioned if wood thrushes that double-brooded and thus moulted their feathers late in the summer, would postpone their migration and subsequently arrive too late to acquire territory on their wintering grounds. But she learned through her geolocator-wearing wood thrushes that even though the late moulting birds crossed later into the tropics, they did not arrive later on their winter territories, contrary to the expectations of Stutchbury and her associates.

In a paper they wrote for the Proceedings of the Royal Society B they concluded, “We suggest the possibility that some individuals prepare to migrate more rapidly than others by investing more heavily in fat storage during the early stages of moult.”

A veery photographed in Chester County, PA, on June 2, 2011

A veery photographed in Chester County, PA, on June 2, 2011 (Photo by Kelly Colgan Azar on Flickr, Creative Commons license)

Other researchers have taken up the challenges and rewards of geolocators including Christopher M. Heckscher and associates of Delaware State University who attached geolocators on 24 veeries in White Clay Creek State Park in Delaware near the southeastern Pennsylvania border. Like the purple martins, veeries also migrate to the tropical forests of South America.

While they wanted to find out whether each veery spent its winter in two different areas in southern Brazil as another ornithologist had proposed, they also wished to discover veeries’ migration routes and timing. Furthermore, in a paper in The Auk, they wrote, “Building on the work of Stutchbury et al…” they wanted “to determine whether geolocator technology can successfully track a terrestrial forest-dwelling songbird from its North American breeding site through dense tropical forests of equatorial South America where day length and night length are equal.”

They proved that point by tracking the veeries to multiple wintering sites first south of the Amazon River in Brazil at five separate locations from November 2 to December 2 and then to second wintering sites as far north as Venezuela and as far south as east-central Bolivia with the other three in widely separated areas in Brazil. They suspect that the “predictable seasonal flooding of lowland forests in Amazonia may be the ultimate factor that prompted the Veeries to relocate.”

From those five birds they “documented three different migratory routes between South and North America and three different routes from the Gulf Coast to Delaware.” And like Stutchbury’s purple martins and wood thrushes, veeries took their time going south but left their wintering grounds in mid-April and returned to Delaware in 17 days.

A gray catbird in Washington, D.C.

A gray catbird in Washington, D.C. (Photo by Steve in Wikimedia, Creative Commons license)

Still another geolocator study, this one of gray catbirds, was by Thomas B. Ryder et al. of the Smithsonian Conservation Biology Institution’s Migratory Bird Center. They pointed out that although geolocators can estimate longitude fairly accurately, latitudinal error can be large—108 miles for purple martins and between 132 and 192 miles for wood thrushes. For this reason, they used both geolocators and bird-banding records “to estimate the migratory connectivity of breeding and nonbreeding populations of Gray Catbirds,” according to their paper in The Auk.

In July of 2009 they put 22 geolocators on gray catbirds in two forest parks near Washington, D.C. These birds left their breeding territory in late August and early September and arrived on wintering grounds in south Florida or Cuba in mid-October. They left those grounds in April and arrived back in the D.C. area in early to mid-May.

Looking at recovered bird-banding data that showed Midwestern gray catbirds overwintered exclusively in Central America and our birds from the mid-Atlantic overwintered in Florida and the Caribbean and combining it with their geolocator studies, they concluded that their research “underscores the importance of geolocators, as well as other tools, to advance our understanding of migratory connectivity.”

A common cuckoo

A common cuckoo (Photo by Ron Knight in Wikimedia, Creative Commons license)

With all this research and much more both here and in Europe using geolocators, bird migration is proving to be more complex and varied than we could have imagined. A recent study of the European common cuckoo using geolocators found them 600 miles away from their usual departure area in northern Europe. Then each cuckoo flew by itself back to its normal route and on to its wintering grounds in central Africa.

In an interview with a National Wildlife reporter, researcher Mikkel Willemoes said that, “They [cuckoos] evaluate their own conditions and adjust their reactions to it, displaying a complicated behavior that we were able to document for the first time in migratory birds.”

He concluded that, “This tells us that bird migration in general is far more complex than previously assumed”—a point we can ponder as we watch our songbirds head south, knowing that only an estimated half of them will survive their migratory journeys and return to us next spring.

Watch a video of Dr. Bridget Stutchbury and associates at the Purple Martin Conservation Association attaching geolocators to purple martins before they set out on their fall migration from Presque Isle State Park, Pennsylvania.

Chimney Swifts

Think of them as “flying cigars,” one of several descriptive nicknames for birds first named “American swifts” by early naturalists and later in the nineteenth century renamed chimney swifts. Their short, bluish-black bodies with silver gray throats and squared-off tails flutter bat-like through the air on long, scythe-shaped wings. “Bows and arrows,” another nickname, can best be imagined when they are flying high in the sky, their wings shaped like bows and their bodies like arrows.

A chimney swift flying overhead

A chimney swift flying overhead (Photo by Dominic Sherony in Wikimedia, Creative Commons license)

Still other nicknames for these flying insect predators are “chimney sweeps” and “chimney swallows.” Like swallows, they rarely alight, but when they do, they cannot perch. They can only cling to vertical rough surfaces even though they have the three toes forward and one toe (hallux) backward of songbirds. But unlike songbirds, chimney swifts can shift their hallux forward to grip the insides of hollow trees in old-growth forests where once they nested and roosted before the arrival of European settlers.

Those settlers quickly cut large trees to build houses with chimneys, and the displaced swifts found new, abundant nesting and roosting sites. Instead of what scientists think were once birds thinly-distributed throughout the eastern forests of North America, chimney swifts became an abundant species that spread as settlers moved into the Great Plains states east of the Rockies from Saskatchewan in Canada south to Texas.

In addition to home chimneys, they have roosted in abandoned large industrial chimneys, stacks, incinerators or air shafts and nested in old wells, abandoned cisterns, outhouses, garages, silos, barns, boathouses, lighthouses, and firewood sheds. Although they probably still nest occasionally in large hollow trees, most notably in abandoned pileated woodpecker nest trees, what were once wilderness birds are now almost solely birds of towns and cities.

I will embed a brief YouTube video showing thousands of chimney swifts flying into an industrial chimney in Gainesville, Florida.

On our mountaintop property in west central Pennsylvania, I rarely see them until the second week in May, yet birders in cities and towns report them as early as mid-April. Widely distributed in every Pennsylvania county, their highest densities occur in Allentown, Erie, Harrisburg, Philadelphia, Wilkes-Barre and especially Pittsburgh’s industrial river corridors, according to the Second Atlas of Breeding Birds in Pennsylvania.

Usually, I first see them in spring in the sky above First Field seining the air for insects. They can scoop up dozens of tiny insects at a time. Their wings beat so fast that many observers once thought they were flapping their wings alternately, which is not aerodynamically possible and was disproved by stroboscopic photography in 1950.

Althea Sherman (left) and her sister Amerlia show Althea’s chimney swift tower to visiting schoolchildren

Althea Sherman (left) and her sister Amerlia show Althea’s chimney swift tower to visiting schoolchildren (Photo from my book Women in the Field: America’s Pioneering Women Naturalists, p. 206; courtesy of Fred Pierce)

Because they spend the daylight hours airborne and their nights in chimneys, researchers have had a difficult time observing their lives. But one woman, Althea Sherman of National, Iowa, designed and had a chimney swift tower built in her backyard. Beginning in 1918, Sherman, who had been watching and writing about birds for decades, spent her arthritic old age (65 to 83) climbing the tower stairs and watching the birds through special windows that allowed her a view from bottom to top of the 28 foot-high tower as the swifts built their nests and raised their young. She also spent many nights with a lighted lamp watching them at rest and proved that they never feed their young then.

Since Sherman’s research, other ornithologists have pieced together the lives of these amazing birds. Once they return to their nesting sites, they engage in trio-flying, which consists of one female and two males following each other and calling as they fly around buildings and trees and then ascend high in the sky where they fly horizontally.

Another display seen all season, which probably helps them keep their monogamous pair bond, consists of one flying behind the other, when the rear bird suddenly snaps its wings upward to form an acute angle.

A chimney swift gripping the wall of a chimney above its nest

A chimney swift gripping the wall of a chimney above its nest (Image by unknown photographer in Birds and Nature n.s. v.2 June-Dec 1905, from Wikimedia, in the public domain)

They return year after year to the same mate and nesting place as Sherman discovered. Both parents construct the nest by breaking off twigs from branches with their feet as they fly, carrying them back to the nest site, and sticking them in place with glutinous saliva they produce from enlarged salivary glands. At eight to 12 twigs a day, it takes them a week to construct a half-moon nest on the side of the chimney strong enough to hold as many as six white eggs.

Both parents incubate the eggs, and the incubating parent waits until the foraging parent returns before leaving the eggs to forage. After an average of 19 days, the eggs hatch, and again both parents brood their naked young and forage for food.

Paul and Georgean Kyle, authors of Chimney Swifts: America’s Mysterious Birds Above the Fireplace, have been watching and rearing chimney swifts since 1983 and write that hatchlings are so active the parent brooding them “appears to be atop a popcorn popper.” When the nestlings settle down to sleep at night one will utter soft, single notes, a monotonous lullaby“me-me-me,” as it sleeps.

An adult chimney swift feeding its nestlings

An adult chimney swift feeding its nestlings (Photo by the U.S. National Park Service at Isle Royale National Park, in Wikimedia, Creative Commons license)

For the first week, parents feed each nestling with a slurry of insect body parts and saliva which they regurgitate into their offspring. Then they start feeding one nestling at a time with a bolus containing dozens of insects. They also allow helpers at the nest to assist them. Usually they are the previous year’s offspring and more often males than females. They will roost with the family at night and may even help incubate the eggs and brood the nestlings.

Many chimney swifts don’t breed every year and while only one breeding pair will occupy a single chimney, they may be joined by roosting unmated birds. Chimney swifts are intensely sociable, feeding together, skimming lakes and rivers for water together, and even flying over each other’s nest chimney and looking inside. The Kyles have seen the brooding parent move aside as if to show off the hatchlings to those stalling over their chimney.

At 19 days of age, the nestlings begin perching on the wall beside their nest and practicing flying. When they are 28 days old, they fly out of the chimney, although they return to roost with their parents and siblings for one to two weeks. As soon as they fledge, they feed themselves the gnats, mosquitoes, flies, winged ants, termites and other airborne insects they find.

Chimney swifts roosting communally in a chimney in Missouri on October 4, 2010

Chimney swifts roosting communally in a chimney in Missouri on October 4, 2010 (Photo by Greg Schechter in Wikipedia, Creative Commons license)

In Pennsylvania they most often nest in June. Migrants begin appearing in the commonwealth by mid-August, and in early September form large communal roosts. Alert observers near such roosts can watch in the evening as swifts, sometimes numbering in the thousands, swirl around the entrance of a commercial chimney before suddenly flying down it at dusk.

Although they may remain as late as early October, most start migrating along our ridges in loose flocks in September, stopping each night in another chimney as they head south. Eventually, they fly over the Gulf of Mexico and then overland to reach their wintering grounds in Peru, northern Chile, and northwest Brazil.

According to the 2014 State of the Birds2014 State of the Birds “Common Birds in Steep Decline,” chimney swifts have lost more than half their global population in 40 years. The North American Breeding Bird Survey reports a 65% decline and estimates a population of 7.8 million. In Pennsylvania we’ve noted a 27% decline between the first and second breeding bird atlasing projects, so in 2005 the chimney swift was listed as a species of Maintenance Concern in our Wildlife Action Plan.

A pair of chimney swifts flying over a park in Miami

A pair of chimney swifts flying over a park in Miami (Photo by Brandon Trentler in Flickr, Creative Commons license)

Researchers aren’t certain why their numbers are declining. One reason may be the loss of masonry and clay chimneys and the capping of chimneys leading to “habitat loss.”

In 2012 a study found that aerial insectivores have experienced guild-wide population declines throughout North America.

Calvin L. Cink, one of two authors of The Birds of North America chimney swift account, writes that the “total impact of temperature extremes and heavy rains…appear to be important for this species.” Furthermore, in a study he did he proved that high summer temperatures for extended periods can kill entire broods. In summary, he concludes that the decline is likely due to changes in prey abundance, chimney numbers, and weather as well as unknown threats during migration and on the wintering grounds.

A chimney swift tower erected in the Brumley Forest Nature Preserve near Hillsborough, N.C.

A chimney swift tower erected in the Brumley Forest Nature Preserve near Hillsborough, N.C. (Photo by bobistraveling on Flickr, Creative Commons license)

To help chimney swifts, the Kyles designed and built a variety of towers to attract chimney swifts and other folks have followed the directions in their book. Most of the towers have attracted the birds as soon as they are constructed.

Here in Pennsylvania, for instance, the Audubon Society of Western Pennsylvania has been building and installing chimney swift towers as part of their Chimney Swift Conservation Program. In addition to constructing them on their Beechwood Farms property, they have partnered with the Allegheny County Parks Foundation to build them in all nine county parks. As of July 2016, they’ve constructed 22 towers in North Park and are starting to build them in South Park.

Cink and his co-author Charles T. Collins also urge that “nest and roost trees (large diameter, hollow trees) should be identified and preserved in old-growth stands of forest,” so that the birds can use their precolonial nesting places.

I enjoy watching them on humid August days and evenings as they fly over First Field, scooping up insects in company with barn swallows and preparing for their long migration south to another continent, and I hope that we can provide enough safe places for them to nest so that the sight of thousands flying down to roost in a large chimney will not become a memory of the past.

I’ll close with a fascinating video of three young chimney swifts being fed by a parent bird.