PA PEREGRINE POPULATIONS:
~ Matt Sharp (4/01)
Pennsylvania was at the heart of the distribution of the Peregrine subspecies
Falco peregrinus anatum, formerly found across eastern North America.
Oologists (egg collectors) eager to include the prized eggs n their collections
eventually reported at least 44 nest sites in the early decades of the
20th century. Cliffs overlooking the Delaware,
Susquehanna, and Juniata rivers and their tributaries were preferred
locations. Nest sites were found in more than 21 PA counties. Nesting
was confirmed even on Philadelphia's City Hall for several years in
the late 40's and 50's. The maximum total breeding population of Peregrines
in Pennsylvania appears to have been 40-50 pairs.
Within the short period between the mid 1940s and
1965 Peregrines experienced a sharp drop in reproductive success and
were quickly eradicated from the eastern United States. Searches in
1964 found no occupied territories in the eastern United States, and
the last documented nesting in Pennsylvania occurred 1961.
In 1975, the Peregrine Fund, based at Cornell University,
began a captive-breeding program to restore the Peregrine Falcon in
the continental United States. Propagation stock was predominately from
falconer's birds of mixed genetic origin, including races from around
the world. Young were released by a method known as hacking. One of
the first locations selected for release was a historic nest site near
Towanda in northeastern Pennsylvania. The young released at that site
were lost to Great Horned Owl predation. As a result of that and other
predation losses (including at Dauphin), Peregrine releases were curtailed
at cliff sites where Great Horned Owl predation was perceived to be
a risk.
Hacking again was carried out in Pennsylvania in
1981 when four young were successfully introduced in downtown Philadelphia.
More than one thousand Peregrines were hacked into the eastern United
States by the Peregrine Fund between 1975 and 1992. By 1998 the Eastern
US population had increased to 1650 pairs.
The Peregrine Fund's Jim Weaver discovered the first
unassisted nesting attempt, in Pennsylvania since the 1950's, during
an inspection of the Walt Whitman Bridge in 1987. Although those eggs
failed to hatch, nestlings were found on the Girard Point Bridge the
following year (1988). Inspection of the site strongly suggested that
previous nesting attempts had gone unnoticed. Nesting on a bridge on
the New Jersey side of the river was documented in 1984. Fledged young
were also discovered near the base of the Commodore Barry Bridge in
1988 and at the Walt Whitman Bridge in 1989, where a pair had been present
since at least 1986. Fledgling young were found in the eastern part
of downtown Philadelphia in 1991, reflecting the existence of a building
nest site in that area.
Currently, nesting apparently takes place annually
in the Philadelphia area at the Commodore Barry, Girard Point, Betsy
Ross, and Turnpike bridges and on the New Jersey side of the Walt Whitman
Bridge. Of these nest sites only the Walt Whitman, and the Girard Point
Bridges are not easily viewable by the public. All the other bridges
can be observed from small public parks/boat launches or from safe wide
road shoulders.
The pair nesting on the Bell Atlantic Tower successfully
fledged 2 young in 1998 from City Hall in downtown Philadelphia, and
one young in 1999, and 2000.
Many nesting adult Peregrine Falcons are banded but
only a few band combinations are known. Lightweight aluminum bands are
attached to the bird's leg above the foot. These bands have serial codes,
which identify the individual bird and the date, and location the bird
was banded. Banding the young birds, and when possible the adults, allows
biologists to track the survivorship of the birds. For example, the
adult female nesting at the Girard Point Bridge was banded in 1992 and
has been returning to that bridge every year since. Adults in Pittsburgh
were hacked (or raised) at cliff sites in the southern Appalachian Mountains.
The female nesting on the Rachael Carson Building in Harrisburg in the
summer of 2000 was hatched on the Girard Point Bridge in Philadelphia.
In addition to banding, new efforts to track the
movements of young birds using satellite telemetry are underway in several
states. This exciting new program is already giving insights into the
lives of falcons born in the Northeastern US. For instance young peregrines,
true to their name, wander widely after leaving the nest and before
migrating south. Some birds have been tracked moving hundreds of miles
north in September and October before going south to the Caribbean and
southeastern US.
The PA Game Commission has secured funding to attach
transmitters to several fledgling Peregrines in PA this year. Hopefully
this program will grow and we will learn more valuable info on the lives
of Peregrines in PA. More information on satellite tracking programs
can be found at
The adult Peregrine population in Pennsylvania appears
to be relatively stable. Although the population is on an increase,
reproductive success at Pennsylvania nest sites, most of which are on
large bridges spanning the Delaware River, has been very poor. The average
1.4 young per pair since 1990 however is encouraging, as is the fact
that a bird from the Girard Point Bridge nested in Harrisburg in the
summer of 2000 indicating that some young from the PA breeding population
are surviving and returning to the state expanding the statewide population.
Although the current population represents an expansion,
there are reasons to believe that the Peregrine Falcon population is
still in jeopardy in Pennsylvania. Reproductive success on bridges has
been very poor for the following reasons: 1) depressed hatching success;
2) premature fledging; 3) mortality of nestlings due to disease; 4)
indirect poisoning; 5) automobile strikes; and 6) disturbance. It is
not clear whether the pairs nesting on area bridges represent a self-sustaining
population.
Nesting pairs should be monitored closely to evaluate
nesting success and young banded to track the population.
Web Cams |
