45 Years of Peregrine Falcon Studies


45 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 15,132. 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 46th annual survey at Assateague was conducted 27 September through 18 October.The survey team expended 162 man-hours in the field, recording 89 sightings of peregrines and capturing 40 different individuals. Four of the falcons captured were previously banded. The 89 sightings included 11 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 10th lowest and captures 23rd lowest among our 46 survey years. A strong nor’easter hit the mid-Atlantic October 1-5 as Hurricane Joaquin moved north offshore. Extremely high winds and tides precluded survey activities on those dates, and we suspect a large proportion of 2015 migrants either passed by or diverted inland during this period. A Hawkwatch site in the Florida Keys recorded around 2,700 peregrine sightings October 8-12, with the unprecedented number of 1,506 passing by on October 10. It is likely that many of those individuals were ones we never had the opportunity to observe at Assateague October 1-5. On the 17 days we were able to conduct survey activities, weather conditions were generally poor for optimum productivity. 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 all or part of 14 of the 17 active survey days. On only one of those north wind days was measurable precipitation recorded, so on most 2015 survey days conditions were unfavorable for observing and capturing peregrines.2015 Assateague Report

During the spring survey period at South Padre Island (SPI) 09-27 April, we expended 143 survey hours in the field, recording 413 sightings and capturing 52 individual peregrines. Of those captured; 3 (5.77 %) were previously banded Padre Returns and 49 (94.23 %) were first banded during the survey. After second year peregrines comprised 69.23 % of the captured sample. The seasonal sighting rate of 28.88 peregrines/10 survey hours is the highest recorded, similar to 2014, though significantly higher than the 21 year SPI mean of 18.79 (±5.10). Not included in the totals above are 2 seasonal recaptures of peregrines initially captured a few hours earlier during the same day.

In autumn, we surveyed SPI from 28 September to 26 October, expending 356 survey hours in the field, recording 793 peregrine falcon observations and capturing 151 individuals. Of those captured 7 (4.64 %) were previously banded and 144 (95.36 %) were first banded this season. Previously banded captures include 4 foreign banded falcons and 3 Padre Returns. The seasonal sighting rate of 22.23 birds/10 survey hours is well above, yet consistent with our 22 year mean of 18.81 (+ 4.15) on SPI. Adults comprised 35.01 % of the age determined sightings (n=597) and 19.21 % of captured peregrines. Not included in the totals above, we recorded 72 sightings of peregrines color marked this season and recaptured 20. The minimum average stopover duration of recaptures on SPI was 4.6 days, ranging from a few hours to 19 days.2015 Padre Report