HOME SWEET HOME
Fifty years ago, there were no peregrine falcons living in Pennsylvania. Today, nesting pairs are successfully raising chicks every year on DRPA's four bridges and in 37 other locations across the region.FANTASTIC FALCONS
Falcons are fast, strong birds of prey that humans first tamed for use in hunting more than 3,000 years ago. With wingspans of more than three feet, peregrine falcons can easily cruise along at 60 mph; when they dive on prey from high up, they can reach 200 mph.
Though today many falcons nest on bridges and other tall manmade structures, in the wild, they like to nest on high cliffs along rivers. Wherever they make their homes, the high perches keep nests safe from mammals that might want to eat falcon eggs or chicks. They also give the birds a great vantage point from which to look for their prey.
Falcons are highly territorial birds, according to F. Arthur McMorris, PhD, Peregrine Falcon Coordinator for the Pennsylvania Game Commission. "Peregrines will not allow another pair of peregrines to nest within a mile of their nest site," he said. "They hunt in a much larger area, as far as 10 miles from their nest, but they can't defend an area that large - it's more than 300 square miles. But they defend the area within a mile of their nest, and the closer to the nest that is, the more vigorous the defense."
Falcons eat birds caught in flight - mostly pigeons, blue jays, and songbirds, but occasionally larger birds such as pheasants and gulls. Youngsters practice their hunting skills on butterflies and dragonflies before graduating to small birds, which they can catch for themselves by two months old. They're full-grown even before they start flying, and head off to look for their own homes (and mates) about a month after they start flying.
"On occasion, some of the young have been relocated to natural cliffs in an attempt to get them to 'imprint' on cliffs and thereby increase the number of peregrines that nest on cliffs rather than bridges," McMorris said. "But they don't stay where they're released: they make up their own minds about where they want to settle down, often hundreds of miles" from where they're born. Wherever they settle, falcons can live up to 15 years.
HOME SWEET HOME
Pennsylvania had traditionally been home to a small but robust population of falcons: there were 44 known nesting sites across the state for most of the 20th century.
Starting around World War II, though, the population began to plummet, and by the early '60s there were no peregrines in Pennsylvania. "The correct word for this is 'extirpation," McMorris said. "Extirpation is being completely wiped out in part of [an animal's] range; extinction is being gone everywhere, forever. By the early 1960s, peregrines had been extirpated from North America east of the Rockies and south of the arctic, as a result of DDT and related pesticides."
DDT was tested and used during World War II against malaria-infected mosquitoes, then adopted as an agricultural insecticide after the war. It turned out, that DDT not only was harmful to humans, it also caused eggshell thinning in birds of prey such as the bald eagle, the osprey - and the peregrine falcon. This meant that the shells of these birds were too fragile to protect the embryos they held, and fewer and fewer birds of these species were born.
Ironically, Rachel Carson's book Silent Spring, which brought the dangers of DDT and other pesticides to the public's attention, didn't come out until 1962, the year after the falcon had been extirpated on the East Coast. Carson is, however, credited as sounding the starting gun for the modern environmental movement, which includes the founding of the Environmental Protection Agency in 1970 and a ban on the use of DDT in the United States starting in 1972.
COME BACK!
A mere two years after DDT was banned in 1972, a nonprofit organization called the Peregrine Fund began an experimental release of captive-raised peregrines. The group ultimately released more than 1,000 birds up and down the eastern United States between 1975 and 1992, when the program was discontinued.It took a few years for the new populations to take hold, but in 1984, a nest was confirmed on the New Jersey side of the Commodore Barry Bridge, and in 1987, a pair of peregrines built a nest on the Walt Whitman Bridge - officially the first nest in Pennsylvania in 30 years. Peregrines were also spotted nesting on the Commodore Barry Bridge and PennDOT's Girard Point Bridge the same year, according to McMorris.
The population has been growing steadily ever since. There were 30 nesting pairs of falcons in Pennsylvania in 2011, and 40 in 2013 - almost back to the pre-DDT number of 44 pairs.
In recognition of this comeback, the peregrine falcon was removed from the federal Endangered Species list in 1999, though it is still considered endangered in Pennsylvania, where it is protected under the state Game and Wildlife Code.
MODERN LIFE
One big difference between the pre-DDT peregrine population and today's is where the birds nest. The majority of the Pennsylvania population in the first half of the 20th century nested in natural spots, though a pair lived atop Philadelphia's City Hall for many years.Since their comeback, however, the vast majority - 80 percent - of Pennsylvania's nesting pairs live atop manmade structures, including buildings, smokestacks and bridges.
The conditions falcons encounter using such structures are different from their natural cliffside homes in some significant ways. For instance, falcons don't build nests out of twigs or other objects - they just scratch out a shallow indentation in the ground where the mother will lay her eggs. The narrow steel ledges in bridges won't allow this, so humans provide nest boxes at over 40 percent of the industrial sites currently occupied by falcons - including the four DRPA bridges where falcons nest.
Falcons also encounter different environmental challenges in their manmade homes. These include human activity, such as maintenance of bridges or window-washing of skyscrapers; vehicular traffic; and a lack of the space fledglings need as they're learning to fly. McMorris and his team, in the Pennsylvania Game Commission's Ten-Year Falcon Management Plan, report, "Although success and productivity at man-made sites has been very good, much of that success was facilitated by active management, conflict resolution and intervention on behalf of fledged young."
DRPA LENDS A HELPING HAND
DRPA staffers do their part in that active management. "We couldn't do what we need to do to manage this recovering species without DRPA's generous help," McMorris said.
First, staffers make the falcons feel at home by providing places for them to nest: they've installed a three-sided plywood structure at each of the four DRPA bridges. The structure provides shelter from the elements, and the gravel floor of the structure mimics the ground where falcons naturally scratch out spots to lay their eggs.
Staffers also help the game commission get up to those nests each year so they can weigh and examine the birds, and put a band around the leg of each new arrival. Those leg bands allow the Pennsylvania game commission - and the commissions of other states - to keep track of peregrine activity across the entire eastern United States and Canada. By checking band IDs, game commission monitors know that falcons born in Pennsylvania are now living as far away as southeastern Canada, and that an adult currently living in Pennsylvania was born in Wisconsin.
DRPA workers also keep an eye on falcon activity day to day. "When we find falcons, babies or whatever, [away from their nest], we call the game commission and read off the number on the bird's leg band so everything's recorded," said Larry Walton, Bridge Director at the Walt Whitman Bridge. Such intervention can save the lives of fledglings that fall from their nests - which is half of the young falcons as they learn how to fly, according to game commission data.
WILD, WILD LIFE
This doesn't mean that bridge workers are treating falcons like pets - they're wild animals. "When we go up to the top of the bridge, sometimes one person has to watch out for the falcons," Walton said. "You have to be careful or the falcon will get you."
Of course, the falcons aren't just freeloaders - they serve a useful purpose on the bridges, keeping down the pigeon population. Pigeons make their nests with their own droppings creating a health hazard. The droppings also contain ammonia and acids that create small electrochemical reactions that rust the steel underneath. Since pigeons are an important part of the falcon diet, the pigeons "won't roost from the anchorages out, they know better," Walton said. "Up top, the pigeons don't go near there - the falcon's always roaming, flying around, squawking."
LOOKING FORWARD
The future of local falcons isn't assured. In the ten-year plan written by McMorris and Game Commission staff, they emphasize "the importance of continued conservation action on behalf of the peregrine falcon."The DRPA looks forward to continuing to partner in that effort.