Peregrine Falcon Management in Pennsylvania
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Published: Mon, 21 May 2018
Peregrine falcons are incredibly creatures, in and around the United States throughout history. They have been captivating our imaginations, being the fastest animal in the world, reaching up to 278 miles per hour in a stoop. According to scientists this should not even be possible, with the average weight of a peregrine mathematically should only be 238 miles an hour. In 1871, with the creation of DDT, their numbers were crushed, landing it on the endangered species list. Recently however, these dazzling acrobats numbers have swooped back up, being removed from the endangered species list in 1999. By nesting in and around large cities, these birds have gotten incredible publicity about their suffering, igniting the compassion of citizens. Despite the fact the bird is doing better, management plans must still be in place in order to ensure the species survival for future generations to enjoy.
Peregrine Falcons are found breeding throughout the world, other than Antarctica. There are at least 19 variations of Peregrine Falcons, with different weights, coloration, and shapes. Pennsylvania, historically boasted two of these subspecies, both the arctic (F.p tundrius) which can be seen migrating through the state during fall time, and the anatum subspecies (F.p anatum) which has had breeding populations.
Peregrine Falcons were extirpated from the state in 1975 due to over collection, and environmental pollution, mainly that of the organochloride DDT. After being placed on the Federal Endangered Animal List, reintroduction efforts were established and DDT was banned. Since then a dramatic recovery has taken place. These birds are repopulating cities like never before taking on the tall skyscrapers and bridges in cities throughout the commonwealth rather than the historic cliffs. Eating nuisance birds, such as pigeons makes them a valuable asset to every city, and the public is more aware of them now than ever. It is my goal to allow these birds to continue to flourish as they have in the past.
The peregrine falcon is a midsized falcon, although the females tend to be larger than males, as with most birds. Females weigh approximately 740-1120 grams and males weigh 550-660 grams. It has a compact build with a relatively short tail and long, tapered wings. Wingspan is typically between 91 and 112 cm. Juveniles are typically darker than adults, with cream colored undersides and a brown back. Adults are typically blue or slate colored on the back, with a light underbelly striated with the blue or grey bars. The face of the peregrine sports a black stripe on each cheek underneath large eyes.
Peregrines require big open areas for hunting and high, inaccessible ledges for nesting. Historically, these birds nested on cliff faces, close to water. Most birds seem to keep a nest site once they have one, typically remaining there for all but a few months out of the year, usually in the middle of winter. Instead of building a nest, peregrines scratch out shallow impressions on the surface of the site and lay a clutch in the spot their talons dug up. It has been noted that some birds will use abandoned nests of the common raven. The nest scratches have to be high enough to be inaccessible to mammalian predators, and be deep enough ledges to accommodate growing chicks, preferably with overhangs to help the birds avoid adverse weather.
Peregrines historically required much taller buildings and bridges, such as the successful nest on the 15th floor of the Rachel Carson State Office building and other nests found even higher in Pittsburg. Peregrines are now using much lower buildings successfully, opening up much more possibilities of nesting sites throughout most large cities in Pennsylvania. Before DDT wiped out most Peregrines in Pennsylvania, only one nest occurred on a building rather than a natural cliff.
Peregrine falcons court each other with aerobatics and calling. Pairs are easily found during February to late April. Peregrines mate for life, until one bird dies, or gets chased off by another suitor. They return to the same place every year, and remain there for most of the year.
Peregrines lay a clutch, usually between three and five eggs, every other day. Incubation starts generally after three eggs are laid and will last between 31 to 35 days. The chicks all hatch around the same time. At around six weeks old the young begin to fledge, with males learning to fly sooner than females in mid-June.
Even after fledging, chicks have been seen being cared for by their parents for months. Birds have been seen with their parents as late as the start of the next breeding season. Successful clutches have been laid by birds as young as one year old. Females begin to breed at two years old typically, with males starting at three years.
Peregrines need a lot of open air around their nests for the fact that they eat live birds exclusively. They are very open to many sized birds, with no real lower limit seen from scientists. Most commonly in Pennsylvania, the peregrine feeds on rock doves, especially in cities, such as Erie, possibly due to their immense availability. It is thought the Peregrine benefited from the clearing of woods for farmland, as this led to more open air for them to hunt for. It is unclear if the reforestation that has occurred since the peregrines demise will affect their ability to come back in certain parts of the state. They may, however, benefit during their comeback due to the increase in large buildings added to cities since their decline in the 1960’s.
Peregrines will use direct pursuit in order to catch slow flying birds. In these pursuits, the falcon will simply fly slightly faster than the bird and catch it in its talons. Peregrines have also been seen using “shepherding,” repeatedly dive bombing a flock of birds such as starlings until one panics and breaks formation so that the falcon may grab it. Most commonly, Peregrines will fly high enough above its prey that it is not visible. Once it is far enough away it will put itself in a stoop, or teardrop shape, allowing it to reach upwards of 200 miles an hour. It aims itself at the prey and essentially knocks it unconscious or kills it with a blow to the head or neck at those speeds. The raptors are not hurt in the process, as they have shock absorbing pads on their feet that do not allow the force to travel into its own body. High speed video has also shown how peregrines hold on to their prey, they strike it with all four toes splayed, and they clamp down on the head of neck in almost the same instance.
Due to an increase of nests occurring on man made buildings, it is more likely that nests will be more readily disturbed. Any maintenance necessary for buildings with nests on them, should try to be done while the parents are off of the premises, and only if there are no chicks on the nest.
Predation on adult peregrines is mainly only possible by the great horned owl. Historically, nests are impervious to almost every mammal due to the sheer ledges they nest on. In cities however, rats may post a threat to young chicks if parents are not vigilant. In Pennsylvania on the Benjamin Franklin Bridge, raccoons have been trapped by that successful nest, though no deaths were reported by raccoons.
In the early twentieth century, there were approximately 350 nesting pairs of peregrines in the Eastern population, with Pennsylvania at the core. The Appalachian Mountains were the primary nest sites, but some birds were also found on the coast of the United States. In Pennsylvania specifically, at least 40 pairs of peregrines were breeding, and most eyries were occupied every year. Oologists and falconers kept the records of these birds throughout the state for egg and young gathering.
Decline in Pennsylvania
Peregrine falcons declined greatly. The Migratory Bird Treaty Act of 1918 regulated the collection of specimens. Eggs and birds were being collected for falconry, and the birds suffered greatly. The populations then took another big hit with the realization that organochloride pesticides, mainly DDT were incredibly effective insect killers. Songbirds would eat the infected bugs, and raptors would eat the affected songbirds. The pesticide would cause the weakened shell of the egg, resulting in the mother crushing the egg while it was trying to incubate it. Between 1950 and 1965 the peregrine falcon decreased exponentially until the entire eastern population was considered extirpated by 1975. It is thought there were approximately 3,875 nesting pairs of peregrines in the United States, meaning that it was never a common raptor. However, that number dropped to a mere 324 nesting pairs in America by 1975, a 90% drop. DDT was banned in 1972 and the peregrine was listed as an endangered species in the United States. In Pennsylvania the last successful mating was in 1957 and pairs were seen until 1959. Thanks to reintroduction projects, the banning of DDT and public support, the peregrine falcon was removed off the Federal list of threatened and Endangered Species in August 25, 1999. In Pennsylvania the peregrine falcon is still considered endangered and is protected under the Game and Wildlife Code.
There Peregrine Fund, a Cornell University sponsored organization began orchestrating the release of captive bred birds to the wild in 1975. They received their birds from falconers, who usually had many subspecies interbred into their birds. Hacking was used, where they raised captive bred animals in an artificial nest until they were able to hunt on their own and no longer visited the nests.
Over 1,000 birds were released between 1975 and 1990 in the Eastern United States. Most of these releases were done on manmade buildings such as skyscrapers or bridges. Once almost 100 pairs had been seen, the Peregrine fund stopped doing widespread releases.
In 1979 the first nesting pairs were seen in New Jersey. Between 19922 and 1998 pairs of falcons began growing at 10% and averaged 1.5 young per nest. When 193 pairs were achieved, the USFWS delisted the birds. In 2003 there is an estimated 336 pairs nesting.
In Pennsylvania specifically, the first chicks were hacked into historic nest sites above rivers along cliffs. Many of these nests were lost, due to predation by Great Horned Owls. The Peregrine fund stopped hacking in Pennsylvania until 1981 when they teamed up with the Pennsylvania Game Commission successfully introducing four birds to the downtown of Philadelphia. The Pennsylvania Game Commission then stepped in to release 59 birds throughout different cities. Young for this release were taken by double clutching, or taking eggs from wild birds soon enough so that they lay another clutch that same breeding season. This means that six birds may be produced by a breeding pair, rather than just three for that year, adding many birds to the population much faster.
Nesting in Pennsylvania has been a slow start. In 1987 the first clutch was seen, but failed. The next year, upon inspection of another nest site, it was seen that attempted nesting had not been noted, but had been occurring. Pre-fledging aged chicks were discovered in 1988 and 1989 where the birds had been nesting since 1986. These birds now nest almost annually. By 2001 there were nine nesting pairs in the state, and by 2011 there are at least 32 locations with nesting pairs. Only five of the nests are found on natural cliff ledges were these birds had historically nested. There was one pair added to the population every two years through 2006, with an astounding eight in 2007, and at least two have been added every year since.
The banding of the legs of peregrine falcons will help biologists track the movement of these birds. This will allow for the understanding of their habitat requirements. The bands will be numbered and lettered so that if the bird is later found deceased, injured, or found again, it can be tracked. While handlers have the bird they should weigh, measure, and check the health of every animal. While at the nest site they should also collect any unhatched eggs, and pellets. The unhatched eggs or egg fragments can be used to determine the egg health, and most importantly, shell thickness. Biologists should use the properly sized band, whether the bird is a female or male, and once a nest site is found, the birds should be banded by three weeks old. Three weeks old is perfect because there is a difference in leg thickness to sex individuals, but young enough they will not try to fly yet. Only certified ornithologists should be doing the banding of these animals.
- Nest Observation
Many peregrines are now preferring to nest on manmade buildings and bridges, and therefore need protected. It is important that no animals are being taken illegally, and that no nests are in danger due to humans. All nest sites should be blockaded off, if there is a possibility of the public walking up to it, or being able to reach it in any fashion. It can be made public where a nest is if it is possible to ensure the birds safety. If there is a possibility to allow public events in which the public can see the nest but not disturb it, such as viewings through windows, which should be encouraged. If there is any sign a nest is being tampered with, or has been unsuccessful for more than four years, cameras will be set up to monitor what is happening to the birds occupying it.
- Modifications of Bridges
If a company so desires to get the publicity of creating a bridge specifically designed to hold a peregrine falcon nesting box, it should be allowed. Such bridges must meet minimum height requirements needed for peregrines. These bridges could also have one way glass, which would appear solid to the nest site, but may allow visitors a privileged look into the nest of a peregrine. The public side of the nest must be far enough away that the public cannot touch it, nor may any noises disturb the nest. This bridge could be modeled off of the Congress Avenue Bridge in Austin for bats.
The peregrine falcon should only be delisted once the population has steadied. Once all nests are producing 1.5 chicks per year and the number of nests has remained steady for a few years, within 5 active nest sites for ten years, then they may be delisted. The target nest site will be built upon the historic 44 nest sites. Historic nest sites are only cliff ledges, and now that we know peregrines can reproduce well on manmade structures, there is an incredible increase in the amount of nests possible throughout Pennsylvania. Once at least 44 active nests have been noted for ten years straight, then delisting may be proposed.
Once the peregrine is taken off the Pennsylvania endangered species list, it shall still be monitored. Chicks will continually by banded, and half of the nests on man made structure should be watched for productivity every year. Falconers, much responsible for the peregrines brought back into the area will be allowed to collect fledglings only after the population has stabilized, or remained constant or growing for five years. Once this occurs, no more than 5% of the peregrines born each year may be taken by falconers.
Relisting should occur if the nests that are being monitored show egg productivity less than 1.5 chicks maturing. If there is a 15% decrease in nesting populations, or peregrine population as a whole relisting should also be considered.
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