Records of Peregrine Falcons nesting on human-made structures date back to the Middle Ages, when they were discovered nesting on the towers of cathedrals.
Records of peregrine falcons nesting on human-made structures date back to the Middle Ages, when they were discovered nesting on the towers of cathedrals.
While the prevalence of this fiercest and fastest of predators on human-made structures may at first seem surprising, bridges and skyscrapers have many of the specific attributes sought by peregrines when selecting nest sites.
Peregrine falcons do not build stick nests. Instead they nest on high, inaccessible cliff ledges, hollowing out an area of sand and gravel known as a "scrape." Peregrine nests are typically located in close proximity to water. They prey primarily on other bird species.
Urban bridges and skyscrapers - with their high, inaccessible ledges and abundant populations of rock pigeons and European starlings - meet many of the peregrine's nesting needs.
Urban sites also come with hazards not associated with cliff sites. Peregrines are highly sensitive to nest disturbance. News helicopters, bridge and building maintenance activities, proximal construction projects and even ordinary human activity near the nest site can cause nest failure.
Bridges are particularly hazardous for nesting peregrines because young falcons tend to fledge (leave the nest) prior to the time they are able to fly. The air currents associated with cliffs tend to rise in updrafts that keep young falcons on the nest ledge as they flap their wings and build up strength for their first flights. Conversely, many bridges have downdrafts and small, isolated ledges that allow young falcons only a minimum of movement. When they do fall, the first step is usually a plunge to the ground or water below.
Fremont Bridge Peregrine Watch: Protecting Portland's Peregrine Falcons
The appearance of peregrines on Portland's Fremont Bridge was viewed initially as a mixed blessing. Biologists anticipated that the nesting falcons would provide the public with a tremendous opportunity to view this recovering species. However they also expected that the survival rate of fledglings at the site would be low.
It was considered to be a "sacrifice site," one that would be of great educational value but one that would not contribute to the gene pool. A collaborative effort between the Audubon Society of Portland and the Oregon Department of Fish and Wildlife has proven that in fact this site could achieve both objectives.
Audubon Society of Portland first became involved with the Fremont Bridge peregrines in 1994. A single youngster fledged from the site that year, and although she survived her initial flight, she slammed into the window of a Rolls Royce dealership on Burnside a few days later. She was transported to Audubon's Wildlife Care Center, where she was treated for her injuries.
A month later she was released back into the care of her parents at the bridge. She was seen hunting and flying around the Fremont in subsequent months and to the best of our knowledge is still flying free.
In 1996, Audubon and ODFW initiated what was to become known as the Portland Peregrine Watch Program. Trained volunteers were stationed under the bridge to provide monitoring, protection and educational outreach. During its first season, Peregrine Watch attracted over 3,000 people who came down to see and learn about peregrines.
Volunteers provide valuable data to biologists regarding the behavior of urban peregrines and also determine a specific nesting chronology.
This information allows biologists to enter the nest at a specific time during the nesting cycle when the young are old enough to thermoregulate, but still young enough that they are not yet mobile and capable of jumping off the ledge.
During nest entry, young peregrines are banded, eggshell fragments and prey remains are collected, blood samples are taken, and the overall health of the chicks is assessed.
Perhaps most importantly, a cadre of dedicated volunteers provided protection for the nest site. During the early part of the season, this involved preventing disturbance of the nesting falcons.
For those who remember when the local television stations first purchased helicopters, one of the advertisements promoting this new news resource was inadvertently filmed less than 100 feet from the nesting Fremont peregrines. A call from a vigilant volunteer led to a quick retreat by the helicopters and prevented almost certain nest failure.
Later in the nesting season, volunteers provided dawn-to-dark protection for prematurely fledging, ground-bound falcons.
At Fremont the young typically spend between one and three days on the ground before they take flight. Much of the volunteer effort goes simply toward keeping curious peregrine watchers back away from the youngsters so that the parents will feel safe to land and feed them.
Volunteers have also pulled young falcons from the river and out of the path of oncoming trains and cars. One youngster even had to be retrieved from a six-foot-deep hole full of excrement that the local homeless community used as a latrine.
Out of 25 youngsters that hatched on the Fremont Bridge between 1994 and 2002, 15 survived the fledging process and twelve of those birds required some sort of intervention or rescue.
The goal in every case was to provide the young falcons with the support and protection necessary to allow them to successfully achieve flight in the wilds of Portland, under the direct care of their parents.