Crows acting up, by Greg7
“Why don’t you just shoot them?”
That’s the reaction of most homeowners when Grant Stokke asks permission to live trap American crows in their backyards. But he hastens to add that they do give him permission.
Stokke is a graduate student who is working with Dr. Margaret Brittingham, professor of wildlife resources at Penn State University, to try to understand the dynamics of winter crow roosts in Pennsylvania, specifically one in and around the city of Lancaster.
I joined Brittingham, Stokke, and field assistant David Burkett for a day of crow field work last January after reading about attempts the winter before to chase the birds from their winter roost in suburban Lancaster County. That winter three townships had called in the United States Department of Agriculture’s Wildlife Services to set out poison bait, which didn’t work very well and angered citizens who opposed using a toxic chemical to kill crows.
Lancaster isn’t the only mid-sized city adjacent to agricultural fields that supports winter crow roosts. Harrisburg, Bethlehem, Scranton, and most recently Lebanon, have a similar problem. So too do a host of other places from Auburn, New York to Riverton, Wyoming.
Most places have tried a combination of noisemakers, shooting, distress calls, and other harassment techniques such as hanging dead crows from trees at their roost site as Lancaster County did the previous winter to chase them away. Sometimes the crows leave, but usually they return.
After all, crows have always formed winter roosts. They used to be in the country, but now that we have provided well-lit malls and city streets that keep away crow predators, specifically their nemesis — the great horned owl — and which are close to agricultural areas that provide food during the day, crows spend the long, dark, winter nights close to humans. Unfortunately, they are not only noisy but incredibly messy, covering buildings, sidewalks, and cars with their excrement.
In the Lancaster area, the crows begin arriving the second week of November and build up their numbers in December. To find out where they are coming from, Stokke and Brittingham have collected stray feathers from American crows, which they subjected to hydrogen ion testing. The test indicated that those crows were in Canada when they grew their feathers, proving that winter roosts consist mostly of migrant crows.
Kevin McGowan, who has been studying American crows in and around Ithaca, New York, since 1988, writes that several of the birds he has tagged there, “have been shot or seen in Pennsylvania during the winter,” so at least a few of the crows come from New York state.
Furthermore, Stokke and Brittingham have discovered that about 25 to 35% of the local crows will occasionally join the roost.
“They will roost at the communal roost some nights and within their family home range the rest of the time. The other 70 to 75% roost within the family home range all the time,” Brittingham said. This finding directly contradicts McGowan’s research in Ithaca in which he found that winter roosts there are made up of migrants and locals and that all locals join the roost.
“I don’t know why there is a difference with Ithaca,” Brittingham said.
“There Is A Light,” by CrowHand
But knowing where they come from doesn’t solve the problem. That’s why Stokke and Brittingham, in their crow behavior study — “Ecology and Management of Urban Crows in Pennsylvania” — are working with local citizens’ groups, local, state and federal government officials, and colleagues at Franklin and Marshall College “to develop a multifaceted approach to reducing the crow problem,” Brittingham said. “But,” she added, “there’s got to be some place for them to go.” Ultimately, Stokke said, they are “looking at whether we might create a place to attract these crows where they won’t be so much of a problem.”
Last winter, instead of poisoning crows, USDA Wildlife Services trained citizens in a variety of harassment techniques including shooting blanks at the birds. First, this harassment moved them from a suburban area northwest of Lancaster, which includes the Park City Mall, where the crows roosted on their 10-acre roof and pecked holes in it. They also made a mess of cars in the parking lot.
Then the crows congregated in center city Lancaster for two weeks. That, Stokke told us, was a rough neighborhood, but still the citizens continued their harassment.
The plan was to move the crows to a county park southwest of Lancaster. It was ideal crow habitat, they thought, but the crows didn’t agree. Instead, they circled and returned to the original northwest light industrial area near farm fields, and that’s where Brittingham and I met up with Stokke and Burkett.
They had already done their pre-dawn roost count, which they estimated to consist of 30 to 35,000 crows. Of those, ten to 20% are the smaller fish crows and the rest are American crows. So far they don’t know where the fish crows are coming from, although Brittingham said that, “Wildlife Services banded a lot of fish crows so we may eventually figure that out.”
Stokke and Burkett also drive a daily route to see where the 42 radio-tagged American crows, half of which are locals and half migrants, spend their days. They took us along for a portion of their route. At the edge of a field across from a housing development, the radio buzzed as we approached an American crow with a white antenna affixed to its back.
“That’s the first one I trapped,” Stokke said. He discovered that this local American crow family of nine or ten birds has less than a square mile of territory. They rarely leave it, although at least two crows did join the Lancaster roost for one night. Such information is hard won, because trapping American crows is not easy, as we found out.
Crows eating French fries, by Greg7
The bait that day was ground beef and peanuts in the shell, but usually it is hot dogs and Chitos, which are cheaper, Stokke told us. At the edge of a corn field, they spent many minutes setting up a portable trap designed by USDA’s Wildlife Services and then carefully camouflaging it with dried grasses. We retreated to their sport utility vehicle and waited for an hour.”All it takes is one brave crow and the rest are in,” Stokke said.
But not one crow came near the trap, not even a fish crow.
These smaller crows, Stokke explained, are easier to trap but they have to release them because the radio-tags are designed for the heavier American crows.
We moved on to a backyard across from a Barnes and Noble bookstore. Cars streamed past on nearby U.S. Route 30 and the Fruitville Pike. A line of tall trees divided the backyard from a corn field. Another copse of trees split the corn field, and it was there that the crows had congregated. We watched for an agonizingly long time as first one crow, then another, flew into the backyard trees for a look at the bait. Finally, one landed near the trap.
“One healthy bird, glossy feathers, lots of body fat,” Brittingham commented. She figured that it was too well-fed to be tempted by their bait. Usually it was a great place to trap crows, but the birds often outsmart them according to Stokke.
While we watched, the crows continued to fly over the bait, but no more birds stopped to look. I felt as frustrated as the researchers.
“They don’t look hungry,” Brittingham said.
By then the crows were engaged in what the scientists call PRA (pre-roosting aggregation) or staging in groups away from the roost, and everywhere we looked we could see flocks of crows calling and chasing.
“I think of them as flying monkeys,” Stokke said, “because they are so smart.” Other researchers agree that the crow family in general is incredibly intelligent. Carolee Caffrey, who studied American crows in Oklahoma, watched a male crow shape a piece of wood into a probe by pecking at its tapered end. He then stuck it into a fence post knot to extract a spider lurking just beyond the reach of his bill.
Caffrey also watched a female American crow defend her nest from a climbing researcher by breaking off pinecones and dropping them on the climber’s head. Altogether, she hit the researcher three out of four tries.
American crows are also the ultimate family-value birds. They mate for life, live in family groups, and older siblings often help feed and protect their younger brothers and sisters. Unlike most other wild creatures, adult American crows never chase away their offspring. When they do leave their family, they return frequently to visit. McGowan, in Ithaca, reported that “one individual (less than one year old) was seen at a compost pile in northern Pennsylvania with a flock of crows, and three weeks later it was back in Ithaca with its parents who were starting nesting. It helped the parents raise young that year, and remained in the area over subsequent winters.”
As the afternoon waned, crows flew more purposefully toward the roost area. In the distance we heard the “pop” of blanks being shot by citizens using nonlethal harassment techniques. The light industrial area hardly looked like a natural area. Under a single conifer surrounded by business buildings, Stokke spotted a banded dead crow. It was not one of their bands so he copied down the number and removed a tail feather for hydrogen ion testing. He also examined it for injuries and found none. The crow was stiff, covered with excrement, and had probably died on the roost the previous night.
The service manager for a nearby car dealer emerged from the back door, and when we told him what we were doing, he launched into his own crow woes. The crows had been using their roof for two weeks.
“We’re just not happy about it,” he said. “They hit a lot of new cars when they take off in the morning — “cars they have to wash before customers arrive.
Eventually, driving through a maze of linked roads behind business buildings, we reached the back of loading docks where we parked. On one side beyond the parking lot were a cattail-filled wetland, a line of tall trees, and the backs of substantial new homes. In front of us was a posted, chain link fence. Beyond that was a large grassy area and then a cement factory.
A crow roost in State College, Pennsylvania, by mandy whale
Standing behind the fence, we watched in awe as a glorious sunset lit the thousands of crows flying in from all directions. Many alighted on the flat-roofed buildings, cawing loudly. Others landed in the line of trees along the wetland, disturbing a large flock of Canada geese that joined the general hubbub and flushing a great blue heron.
What a spectacular, yet ludicrous sight. Stokke, who had previously studied common ravens in a remote area of Washington state, could not imagine a more stark contrast to his present situation — malls and business buildings, housing developments, and crushing traffic.
Yet nature persisted and, in fact, preferred the city/suburban landscape. In our rush to expand and develop we had created ideal winter habitat for the gregarious, intelligent crows. Safe from predators and warmed by the “heat bubble,” rising from the buildings which can be five to ten degrees higher than the surrounding countryside, the crows slowly settled down for the night.
To learn how you can support local volunteers in Lancaster and protect the crows from lethal management, visit the website of the Lancaster County Crow Coalition.
All photos used by permission.
January is great horned owl month on our mountain. Not only are their hoots the quintessential signature of long, silent, moonlit, winter nights, but they are also more visible in the day time. During the rest of the year I may have an occasional glimpse of one as it flies from a roost, but my best sightings have occurred in January, most notably January 18, 1993 and January 19, 1998. In both instances the mobbing calls of American crows alerted me to their silent, motionless presence.
The 1993 sighting occurred on a windy, 20 degree, sunny morning. I tracked scolding crows to Margaret’s Woods, but I could not see any enemy they were mobbing. Still they persisted, so I finally walked toward them up the Steiner-Scott Trail (a recent logging road that leads to the top of Sapsucker Ridge).
Halfway along the trail, I spotted a large, beige-colored blob on the branch of a tree swathed in grapevines. To my delight that “blob” was a great horned owl, bathed in sunlight and not inclined to fly. I sat below it, my back against a tree, and watched as a pair of black-capped chickadees flew in close to scold the owl. Then a tufted titmouse joined the chickadees as they called a couple feet from the owl’s head. It blinked its eyes open to look and the birds flew off, so it closed its eyes again.
After a few moments, it again opened its eyes and slowly turned its head to the side. The eye toward me watched as I stood up. After I took a couple steps, it flew off.
I was amazed at how perfectly it had blended into the tree branch and grapevines. Without my binoculars I never would have distinguished the owl with its perfect camouflage. I thanked the crows, which for once had had something to crow about.
According to biologist Bernd Heinrich, who studied mobbing behavior while raising an orphaned great horned owl, birds that are permanent residents of an area, such as the tufted titmouse and chickadees I observed, use mobbing to encourage owls to move on. He further hypothesizes that “since crows have conspicuous roosts to which they return each night, the ‘move-on’ hypothesis should apply especially strongly to them. And, indeed, the vigor of the crows’ mobbing in winter is surpassed by few other birds, even in spring.” Furthermore, after analyzing owl pellets in his woods, he discovered that crows were the principal prey item of great horned owls there.
Whether or not our great horned owls prefer crows, mobbing crows again “showed” me great horned owls last January on an inclement morning. A light snow fell as I walked Greenbrier and Ten Springs trails through a forest that had been clearcut seven winters ago. But as I neared the end of Ten Springs Trail, five crows cawed loudly in the uncut forest ahead. I sat down in the heavily wooded hollow and, looking uphill, I quickly spotted the shape of a great horned owl sitting out on the end of a tree branch. It looked as if it were unbalanced, an extension of a branch that leaned but, in fact, the branch had a projection against which the owl was braced.
I sat and watched for fifteen minutes as two crows remained nearby, occasionally emitting low noises of approbation in their throats. Then I spotted a second, slightly larger owl sitting tightly against the tree trunk. No doubt it was a pair–the larger female against the trunk, the smaller male out on the branch. I’d never seen a pair before so I continued watching them until I was too stiff and cold to remain any longer.
As I stood up, stretched my cramped legs, and continued my walk, the male, which had had its head turned away from me the entire time, finally looked down at me. The female never moved. In both owls, it had been their ear tufts that had made it possible for me to first pick them out despite their frozen stances and excellent camouflage.
Heinrich also speculates on the use of ear tufts. Fifty of the world’s 131 species of owls have them, yet no one is sure what function they serve, if any. In the case of Heinrich’s captive great horned owl, Bubo, he says that “he has a fondness for perching on broken-off tree trunks, where he quite effectively impersonates the top of the stub” and wonders if the reasons for ear tufts could be that they mimic the ears of mammals which helps them in their threat displays, they serve as short-range species-recognition marks, and/or they provide added camouflage. Perhaps ear tufts helped to camouflage Bubo but not the wild owls I observed.
I assumed that the pair I saw was the same couple that hooted throughout the winter near our home since a breeding pair needs a square mile of good territory, which is exactly what we own. On February 13 and 14 a pair called from trees on top of Sapsucker Ridge in early evening, and we could easily see them with our binoculars. By February 18 they had moved to the small woods above our garage and hooted most evenings and early mornings until March 16. The female hoots are shorter and higher pitched than those of the male. Researcher John T. Emlen had sharp enough ears to detect grunting noises the male makes before he hoots and in between hooting to stimulate the female to hoot. The female hooting in turn stimulates the male to continue hooting. All of this is part of the annual courtship ritual between birds that mate for life.
Solitary hooting by males is done to advertise and defend their territories, which they hold on to throughout the year. Most great horned owls remain in the same area where they hatched unless food is scarce. Then the young may move on, as far as 837 miles in one case. But established pairs may choose not to breed if food is scarce because faithfulness to their territory is stronger than the urge to breed in most paired great horned owls.
When there is enough food, courtship takes place mostly in early January and February evenings and includes calling, displaying, mate-feeding and allo-preening. First the male approaches the female by hooting and landing on perches close to her. She may answer him if she is interested. He then performs such displays as fluffing his body feathers, partly spreading his wings and bowing, walking and hopping on the ground, and/or throwing his head back and repeatedly snapping his bill. If she doesn’t fluff her feathers or snap her bill at him–both signals that she is not interested–he sits on the same perch with her, gradually sidling closer, until they preen each other by pecking at the feathers around their mate’s bill and/or head and sometimes emitting a variety of barks, screams, whistles and hoots. Then both hop and bow, and occasionally a male brings in food for them before they mate. After mating, the pair often roosts together during the day like the pair I observed last January.
Great horned owls never build their own nests. Instead they occupy the used nests of red-tailed hawks, crows, ravens, herons or squirrels. Last winter I examined dozens of old squirrel nests in search of nesting great horned owls but never found any. Since they occupy their nests and lay their one to four white eggs from mid-February to early March in Pennsylvania, deserted nests are easy for the owls to preempt. The female, occasionally relieved by the male, incubates the eggs from 28 to 30 days, but once the eggs hatch, the female keeps the young warm while the male provides food for the family.
The young hatch over several days, according to the order in which the eggs were laid. if food is abundant, all of them survive and thrive. If it isn’t, the largest owlet is fed first and competition is fierce. Often the youngest (and weakest) die.
At two weeks of age their eyes are open, at three brooding stops, at four to five weeks they can move about the nest, and at six to eight weeks they leave the nest, perching on nearby branches where their parents continue to feed them. When they are nine to ten weeks old, they attempt to fly and gradually, after ten more weeks, they have learned to fly and been taught by their parents to hunt well enough to disperse, although half of all young do not survive their first year.
Humans have been their most implacable enemies. Because great horned owls eat popular game species such as ruffed grouse, eastern cottontails and ring-necked pheasants in Pennsylvania, persecution of great horned owls in the form of bounties were in place from 1937 to 1941 and from 1944 to 1966. The Federal Migratory Bird Treaty Act of 1972 forbade the taking of all raptors including great horned owls, and since that time their numbers have increased.
Great horned owls are opportunistic feeders and tend to eat whatever is available including rabbits, foxes, porcupines, skunks, other owls, hawks, crows, feral cats, mice and rats. They fish in water up to their stomachs for fish, turtles, crayfish and frogs, although Heinrich’s captive Bubo distinguished between wood frogs, which he relished, and bullfrogs, which he disliked.
One researcher in Wisconsin watched as a great horned owl perched on a tamarack tree, bobbed its head, flew off into a gradual climb, flipped back in midair, and grabbed large, chunky beetles, which it carried back to its perch to eat. Another owl was observed as it ripped a muskrat from a trap and still another tried to grab a raccoon from a hunter’s shoulder. Bubo dined happily on fresh kills made by Heinrich’s cat–mice, voles, shrews, and songbirds–and on fresh road kills collected by Heinrich. Heinrich also fed him red squirrels that he shot.
Years ago, when we raised Muscovy ducks, we arrived home after sunset and watched a great horned owl trying to fly off with our alpha male Muscovy named Big John. Big John flapped valiantly as the owl aborted a couple liftoffs before giving up. In the end, though, it was a raccoon that wiped out all 27 of our ducks as they roosted in the barn.
A food study done in Pennsylvania from 1965 until 1986 by biologists Wink, Senner and Goodrich analyzed owl pellets from 17 counties throughout the commonwealth and found that although eastern cottontail rabbits were a favorite prey item of great horned owls (15%), ruffed grouse prey ranged from 9% in northwestern Pennsylvania to 4% in southeast Pennsylvania and pheasants a mere 3%. The overwhelming favorite prey, however, were Norway rats (24%). But if the diet was based on the weight of the prey, opossums constituted 33%, rabbits 28% and Norway rats 12%.
The rats are an indication of how popular farm habitat is with great horned owls. According to a study carried out by Yahner and Morrell from 1986 to 1989 in south central Pennsylvania, great horned owls hunted most extensively in agricultural areas and adjoining woodlands. In fact, the more fragmented the landscape, the better the opportunities for great horned owls.
Because they will eat almost anything and live almost anywhere–from Arctic Canada and Alaska to the southern tip of South America–great horned owls will survive and thrive long after specialists have gone extinct. That’s good news for those of us who define our winter nights by the hooting of great horned owls.