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Assateague Island Peregrine Falcon Survey 2003 Report |
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RESULTS AND DISCUSSION The total of 572 peregrines sighted (table 2) was 10th highest in the 34 years of the survey, and sightings per 10 man-hours 11th highest. The 155 captures matched another year (2000) as 10th highest overall, and captures per 10 man-hours were 10th highest as well. Among individuals identified by age class, adults comprised 13.72% of those sighted (table 3), only slightly under our 34-year mean of 14.89%. We are awaiting details from the USGS Bird Banding laboratory on the ten recoveries of previously banded falcons. Five were individuals from the new race of peregrines established in the East through captive propagation and release. As was the case in 1999-2002, we strongly suspect the adult female we outfitted with a PTT in 1996 and captured again in 1997 and 1998 was back on her McCabe Tract territory. A banded adult female was continually present, using familiar perches, and defending the area she frequents from eagles; she could not be captured due to lack of vehicle access to that area. Sightings and captures by sector (table 4) warrant some discussion. The McCabe Tract's major washover zones feature beach to bay sand flats in some areas. This is favorable habitat for migrating peregrines in the autumn, as well as good breeding habitat for the endangered piping plover (Charadrius melodus). In 2003 our NPS permit continued to restrict operations to the beachfront of the McCabe Tract due to the presence of the federally threatened and Maryland endangered plant Sea Beach Amaranth (Amaranthus pumilus). This restriction limits our sighting and capture potential, and makes the occurrence of foot traffic and other authorized vehicles along that same beachfront more debilitating to our prospects during those events. While the McCabe Tract has in the past sometimes rivaled the Wash Flats as the island’s most productive sector, this year’s relative productivity was barely one-third. A possible explanation is that many falcons migrate offshore to bypass continued intense development to the north of Assateague. Those individuals may tend to return to the coast when seeing the more hospitable Assateague beach, but the vector of that corrected course may place their landfall to the south of the McCabe Tract. Because of its very narrow beachfront, development and public use, the Assateague State Park is seldom utilized by migrant peregrines; we spent less than two hours there. The Access Road in Maryland and Service Road in Virginia are utilized only for travel between other sectors, and offer few possibilities for anything more than observations. The Maryland Beach continues to widen somewhat due to erosion westward of the dune line, with significant washover areas where sand and water have taken out or buried vegetation. The Refuge Beach in Virginia is generally narrower and less conducive to effective capture attempts due to a more intact barrier dune system, yet productivity there is usually higher than on the Maryland Beach. 2003 was no exception, and this is almost certainly due to the very intensive public use of four-wheel drive vehicles on the Maryland Beach, particularly on weekends. On September 28, for instance, Yates counted 153 oversand vehicles on this 12-mile stretch of beach. The Hook's suitability for observing and capturing peregrines is still tied to the amount of public use at any given time. Although vegetative encroachment continues, there is still good resting habitat and the area’s topography naturally draws peregrines in good numbers. It is suspected that, absent public use, productivity on this southernmost sector would often exceed that of all others on the island. In 2003 public usage of the Hook was generally heavy. Although sighting productivity was second only to that on the Wash Flats, many individuals were observed moving past the area. The Wash Flats, in its natural state, was a huge washover area of beach to bay sand flats and was prime peregrine and shorebird habitat. Construction and maintenance of the stabilized barrier dune system have resulted in dramatic vegetative growth. During the past 20 seasons alone more than half the open area has been lost as good hunting and resting habitat for migrant peregrines and for shorebird foraging and nesting. Hope for the future lies in CNWR’s: 1) physical removal of much of the vegetation west of the dune line, a project underway during this year’s survey; and 2) current policy of not maintaining the barrier dune north of D-Dike. This will foster a more natural progression of barrier island geomorphology and may return this sector to its natural state, but only after many years and only if interior dikes are also allowed to erode. The remaining open area of the Wash Flats was inundated over most of the summer with rainwater, and this promoted dense vegetative growth (particularly dwarf glasswort, Salicornia bigelovii). We were unable to enter the area for extended periods due to flooding, but this sector was by far our most productive in 2003 when accessible. On 14 October 1993 two adult female peregrines
were equipped at Assateague with PTTs tracked and globally One of the 1993 adults wintered in a unique wetland habitat, at 14,000 feet in the central Argentine altiplano. Members of our research team reached this area in February of 1994, where they made detailed observations on the wintering behavior of the falcon and did a complete habitat analysis and avifauna survey. It was determined that an immature female peregrine also wintered in this small wetland with the adult we tracked. Since that time we have continued to refine, miniaturize and apply these technologies to unlock the remaining mysteries of the tundra peregrine's ecology. This subspecies was removed from the list of endangered species entirely on the basis of population trends evident from breeding ground surveys in the Arctic and migration studies in temperate zone flyways. Although contaminant levels have declined, it still faces toxic threats to the food chains in its Central and South American wintering grounds. These technologies comprise an invaluable tool in identifying critical habitats and in pinpointing and mitigating global sources of contaminants affecting peregrines and the other Neotropical migrants with which their life histories are so irrevocably intertwined. On October 7th and 8th we outfitted adult females with
PTTs. The October 7 female (figure 1) left the North Carolina coast and
traveled offshore, making landfall in Florida. She went through the Bahamas,
Cuba, and Haiti before reaching the coast of South America near the Columbia/Venezuela
border. She is currently in Brazil, below the Amazon River. The October
8 female (figure 2) went through interior North Carolina and appeared
on the coast again in Georgia. Passing through the Florida Keys and Cuba,
she reached her apparent wintering area in coastal Belize only 12 days
after her release at Assateague. In 2003 an adult female was present during parts of most days on the Wash Flats tower. She proved to be the most highly territorial individual present in many years. We observed her in the process of ejecting at least 18 migrant peregrines that were attempting to utilize the habitat, and she even extended her aggression to at least one hapless cooper’s hawk. In collaboration with Dr. Robert Dusek of the USGS National Wildlife Health Center, we collected 96 blood samples from migrant peregrines this fall. These will be analyzed for the presence of West Nile Virus (WNV), a mosquito-borne virus that is becoming a significant threat to humans and wildlife. Birds are particularly susceptible to WNV, and if tundra peregrines become carriers this malady could quickly spread throughout their extensive range. To date, one Assateague migrant has tested positive for WNV. An adult female captured on October 11, 2001 had a titer of >=1:1400, which was the highest of all 18 positive samples among those Dusek submitted that autumn. Assateague Island 2003 Report Page 1 |
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positioned
by the Argos/Tiros system. Developed through our joint project of many
years with the U.S. Army, the USFWS, and the Applied Physics Laboratory
of Johns Hopkins University, these 27-gram PTTs were equipped with activity,
temperature and battery voltage sensors, and transmitted signals at programmed
intervals to orbiting satellites. The accuracy of the system in locating
the PTT depends upon several factors, and may range from several hundred
meters to several miles.