47 Years of Peregrine Falcon Studies


47 Years of Peregrine Falcon Studies

Earthspan principals conduct long-term studies on migrating peregrines at Assateague Island, MD/VA (autumn since 1970) and Padre Island, TX (autumn and spring since autumn 1977). We have expended almost 54,000 man-hours of survey time in observing over 69,000 peregrines and capturing 15,699. The tundra Peregrine has made a significant recovery and has been removed from the list of endangered species, yet continued monitoring of populations is imperative. Because of the continuity and standard method for data collection these surveys have become an essential tool in that effort.  Our database at Assateague includes sightings of every other raptor we have observed on the Island since 1970. Some 90% of all observations there have been recorded by three experienced individuals, who have also conducted springtime studies at Padre Island. At Padre a more diverse cast of highly qualified individuals has participated.

Our work in these studies with satellite-received telemetry allows us to continue elucidating previously undescribed aspects of the tundra Peregrine’s wintering biology and continental migration and to identify critical habitats. Given available technologies, Assateague and Padre remain ideal laboratories in which to study and address present and future issues of concern to Peregrines, other Neotropical migrants, and humans. In recent years we have studied emerging infectious pathogens such as West Nile Virus and Avian Influenza in partnership with U.S. Government entities, and addressed contaminants through studies related to the 2010 Gulf oil spill.

In 2008 our database allowed us to provide an Expert Declaration on the Draft Environmental Assessment and Management Plan for Take of Migrant Peregrine Falcons in the United States for Use in Falconry. Among other points, we concluded that the standardized average number of migrating Peregrines we observed at Assateague over the preceding 29 years was essentially the same as that seen more than six decades ago (1939-1944), before DDT had serious adverse effects on the reproductive potential of the Peregrine in North America. Our work at Assateague and Padre Islands represents the bulk of tundra Peregrine Falcons banded within the continental United States since the establishment of the Bird Banding Laboratory by the Department of the Interior.  Furthermore, our overall database constitutes the most significant and longest continuous monitoring study on this falcon in the Americas. Long-term studies such as ours are essential to monitoring the stability of wildlife populations, particularly in light of rapid changes that may occur due to contaminants, infectious diseases, habitat loss, climate change and other factors. By the long-term and standardized nature of our studies, we have established levels of observation in stable populations that will quickly raise future concerns if not achieved over a several year period.

Assateague Survey 2017 – From 27 September to 18 October the survey team expended 213 man-hours in the field, recording 279 sightings of Peregrines and capturing 65 different individuals. Five of the falcons captured were previously banded. The 279 sightings included 88 observations of individuals previously captured during the survey. We exclude resident Peregrines but include these other known duplicates in tables and discussion. This is to allow more direct comparisons among our data and those from pre-survey Assateague counts (dating from 1939) and other projects where protocols do not allow identification of duplicates.

Sightings per 10 man-hours were 13th highest and captures 20th highest among our 48 survey years. Overall productivity on the 23 survey days was reasonable considering the frequent northerly winds. Although some north wind days can be productive if overcast skies and light rain are present, most days with winds from the north quarter assist the migrants in moving south and we observe few. In reviewing Assateague State Park weather records to confirm our observations, we found that winds had a northerly component on 14 survey days; rain in any amount was associated with only three of those days. Productivity also suffered on 10 October when many migrants streamed through on strong north winds that precluded safe and effective capture. Generally we experienced many days in 2017 where Peregrines were not observed in numbers that, based on previous experience, weather would have suggested. Among individuals identified by age class adults comprised 9.79% of those identified, or well below our 48-year mean of 14.87%. 2017′s unusually large percentage (31%) of known duplicates accounts for the low adult figure, since only three of those duplicates were adults. 2017 Assteague Report

Padre Surveys 2017 – During the spring survey period from 12 April to 02 May, we expended 191 survey hours in the field, recording 457 sightings and capturing 36 individual Peregrines. Of those captured; three (8.33 %) were previously banded Padre Returns and 33 (91.67 %) were first banded during the survey. After second year (ASY) Peregrines comprised 66.67 % of the captured sample. The seasonal sighting rate of 23.96 Peregrines/10 survey hours is among the higher rates recorded and consistent with our 23 year SPI mean of 19.44 (±5.37). Not included in the totals above are five seasonal recaptures, whose minimum average stopover duration on SPI was 1.8 days, ranging from a few hours to six days.

In autumn, we surveyed Padre Island from 27 September to 26 October, expending 429 survey hours in the field, recording 635 new Peregrine Falcon observations and capturing 131 individuals. Of those captured seven (5.34 %) were previously banded and 124 (94.67 %) were first banded this season. Previously banded captures include one foreign banded falcon and six Padre Returns. The seasonal sighting rate of 14.80 birds/10 survey hours is well below, though within the lowest range of our 24 year mean 18.71 (± 4.07) on SPI. Adults comprised 31.02% of the age determined sightings (n=548) and 25.19 % of captured Peregrines. Not included in the totals above, we recorded 49 sightings of Peregrines color marked this season and recaptured 13. The minimum average stopover duration of recaptures on SPI was 3.0 days, ranging from a few hours to eight days. 2017 Padre Report