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Peregrine Survey Protocol


When a Peregrine Falcon nesting territory is established, there is a 95% chance that the territory will continue to be occupied during the next, and following, nesting seasons. Therefore, the species lends itself to continuing population studies.

During the period since DDT was banned (1972) and population recovery efforts were undertaken in California by the UC Santa Cruz Predatory Bird Research Group (1975), we have witnessed a remarkable population increase that continues today. We now focus our attention on the San Francisco Bay Area population because Peregrine Falcons have been removed from the Endangered Species list and because monitoring of trends in this population can inform us of larger ecosystem health issues.

 The pre-DDT San Francisco Bay Peregrine Falcon population included just two known pairs. The same area now supports about two dozen pairs of falcons; most nest locations are found on manmade structures.


We survey San Francisco Bay Area Peregrine Falcons twice annually: For our Winter Survey, we organize a fixed point survey that occurs between 0900 and 1100 on the second Saturday of each December, and coordinate students and volunteers and local community leaders at forty-eight observation posts around San Francisco Bay. Please contact us in early November to express an interest in participating in the winter survey.

Experienced observers who include university students and members of the peregrine falcon-watching community survey approximately thirty nest territories in the San Francisco Bay Area for occupancy and productivity. We band nestlings to learn more about longevity, nest site tenacity, and juvenile dispersal at a sample of the locations.

Observing Breeding Behavior

IMPORTANT: If at any time, the falcons begin “cacking” loudly, the observer is too close to the nest and should retreat immediately! Disturbances at the nest site that cause extended periods of cacking vocalizations can lead to nest failure. Peregrines especially dislike trespassers above the nest cliff.

This survey seeks to measure three parameters of breeding behavior:

Occupied Territory - a territory where either two adults are present, or there is evidence of reproduction (e.g., one adult is observed sitting low in the nest, or eggs or young are seen). Occupancy must be established for at least one of the two (or more) 4-hour site visits.

Nest Success - a nest in which at least one young, at least 10 days old is observed or known to exist.

Productive (optional) - the number of young raised to 34 days or older.

Some behaviors can be misinterpreted as "nest-failure". To be sure that nesting activity has ceased at a site, it is important to observe the site carefully for a minimum of four hours. Many pairs begin the nesting cycle anew after nesting failure at the egg stage, usually in another eyrie.

Determining Occupancy, Success, & Productivity

It is difficult to improve on Janet Linthicum's "Observing Breeding Behavior" (Cade, et. al. 1996) for determining territory occupancy, nest success, and productivity, so we include it here in full. But since most surveyors will not be able to observe young at close hand, we offer the following method of determining the presence of young 10 days of age or more to ascertain “nesting success”.

By observing young: Between the ages of 10 and 14 days of age, young peregrines acquire a "second down" making it possible for them to maintain body heat without constant brooding by an adult. These extended absences from the nest by adults are sometimes interpreted as nest failures. Watching carefully from a distance for prey delivery is the best way to determine the presence of young more than 10 days of age. At eyries where young are visible, they begin to appear quite alert and sit upright to preen or when disturbed by the time they reach fifteen days of age.

By observing adults: In many cases it is impossible to look directly into the eyrie and observe adults and young in the nest so we have to rely on our observations of adult behavior in the vicinity of the nest to determine the presence of eggs or young. BY NO MEANS should an observer attempt to see into a nest if it might cause disturbance to the adults. An adult is almost always in the nest if the incubation of eggs is occurring so the observer must focus attention upon the eyrie. When a food exchange occurs, the male delivers food to the female in the air or at a perch and immediately goes to the nest ledge to cover the eggs while she eats. If young are present, the female may briefly pluck the food item before taking it to the nest.

Download the verbatim PDF text of "Observing Breeding Behavior" contained in, Guide to Management of Peregrine Falcons at the Eyrie, by Cade, Enderson, and Linthicum, and published by The Peregrine Fund. We thank the authors and The Peregrine Fund for permission to reprint these guidelines here.

Survey Results

December 2010: Volunteers working in concert with UC Santa Cruz student leaders, Zach Michelson and Teague Scott, made the first Bay Area Peregrine Falcon Census a great success. SCPBRG observers combined with Golden Gate Raptor Observatory members and Audubon Association members to record forty-six peregrine falcon sightings at forty-eight locations. An analysis of the results revealed that thirty-nine (39) different falcons were seen on the second Saturday in December, 2010.

December 2011: There were forty-six (46) sightings of Peregrine Falcons during the two-hour survey that included thirty-seven (37) different birds. We analyze the data forms to identify the fifteen minute block of time with the most falcons in view for each of six sectors. The sector subtotals are added together to reveal the total number of Peregrine Falcons counted during the survey at forty-eight established observation posts around the San Francisco Bay.