46 Years of Peregrine Falcon Studies


46 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 more than 52,000 man-hours of survey time in observing over 66,000 peregrines and capturing 15,229. 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. Over 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.

The 47th annual survey at Assateague was conducted 27 September through 17 October.The survey team expended 189 man-hours in the field, recording 317 sightings of peregrines and capturing 97 different individuals. Six of the falcons captured were previously banded. The 317 sightings included 61 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 earlier Assateague counts (dating from 1939) and other projects where protocols do not allow identification of duplicates.

Sightings per 10 man-hours were 7th highest and captures 6th highest among our 47 survey years.We were unable to conduct survey activities for 2.5 days due to high winds and/or tides, but productivity on the 19 active survey days was high considering the persistent 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 weather records from the Ocean City airport to confirm our observations, we found that winds had a northerly component on each of the initial 14 active survey days. On the following three survey days only four total hours were exempt from that pattern. We finally received winds from the southerly quarter on the final two survey days, after most of the migrants had passed. So while winds were generally unfavorable (as in 2015) for observing and capturing Peregrines on 17 of 19 2016 survey days, more rain and overcast skies than last year increased our productivity this year. 2016 Assateague Report

During the spring survey period at South Padre Island (SPI) from 14 April to 03 May, we expended 168 survey hours in the field, recording 483 sightings and capturing 58 individual peregrines. Of those captured 6 (10.34 %) were previously banded Padre returns and 52 (89.66 %) were first banded during the survey. After second year (ASY) peregrines comprised 70.69 % of the captured sample. The seasonal sighting rate of 28.64 peregrines/10 survey hours is the second highest recorded, significantly higher than the 22 year SPI mean of 19.23 (±5.40). Not included in the totals above are 3 seasonal recaptures of peregrines initially captured a few hours earlier or one, the previous day.

In autumn, we surveyed SPI from 25 September to 22 October, expending 345 survey hours in the field, recording 702 peregrine falcon observations and capturing 180 individuals. Of those captured 6 (3.33 %) were previously banded and 174 (96.67 %) were first banded this season. Previously banded captures include 1 foreign banded falcon and 5 Padre returns. The seasonal sighting rate of 20.34 birds/10 survey hours is well above, yet consistent with our 23 year mean of 18.87 (+ 4.07) on SPI. Adults comprised 19.58% of the age determined sightings (n=618) and 6.67 % of captured peregrines. Not included in the totals above, we recorded 82 sightings of peregrines color marked this season and recaptured 32. The minimum average stopover duration of recaptures on SPI was 7.3 days, ranging from a few hours to 20 days.2016 Padre Report