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SPRING and AUTUMN 2003 PEREGRINE FALCON MIGRATION STUDIES AT SOUTH PADRE ISLAND, TEXAS |
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CONDUCTED UNDER TEXAS PARKS AND WILDLIFE PERMIT SPR-0390-047 USGS MASTER BIRD BANDING PERMIT 22234 The spring 2003 Padre Island Peregrine Falcon Survey was conducted from 10 April through 25 April. During that period 162 hours of observation were made. A total of 315 peregrine falcons were observed and 47 (14.9%) captured. Of those captured, 22 birds were previously (46%) banded on South Padre Island. The number captured for the first time this spring totaled 32 (68%). Blood samples were obtained from 40 falcons and sent to Dr. Robert McLean of the USGS National Wildlife Health Center for continued monitoring for West Nile Virus. The autumn survey was conducted from 25 September through 21 October. During that period 302 hours of observation were made. A total of 589 peregrine falcons were observed and 171 captured (29%). Of those captured 10 were previously banded (5.8%). The number captured for the first time this autumn totaled 161 (94.2%). Blood samples were obtained from 151 birds and sent to Dr. Robert McLean of the USGS National Wildlife Health Center for continued monitoring for West Nile Virus. INTRODUCTION Coastal areas along the Gulf Coast of Mexico are well known as concentration points for migrant peregrine falcons (Enderson 1969). Both spring and autumn counts of migrant peregrines have been conducted at North and South Padre Island, where falcons use the beach and wind-tidal flats for hunting and resting. Padre Island also serves as a major staging area for spring and autumn migrants; some individuals have been known to stay on the island for 30 days or longer during peak periods of migration (Riddle et al. 1978-1985 in annual reports to USFWS). North and South Padre Island have been under investigation as an autumn peregrine falcon concentration point since the early 1960’s (Enderson 1963, Hunt et al. 1975). Northward migrating peregrine falcons are also numerous on North and South Padre Islands in spring (Hunt et al. 1980). Since 1977, 6,954 peregrine falcons have been captured and banded at Padre Island. Padre Island is the only known locality in the Western Hemisphere where peregrine falcons (Falco peregrinus anatum and F. p. tundrius) can be found in concentrations during the spring migration. OBJECTIVES
The objectives of the Padre Island Peregrine Falcon
Survey include: 1) monitor population trends through band returns and
sightings; METHODS USED IN SPRING 2003 Throughout the survey period, a team of 2 or 3 person’s surveyed South Padre Island using all-terrain vehicles (ATVs) from dawn to dusk as weather conditions allowed. Personnel on ATVs were not deployed when substantial precipitation or lightning occurred. After heavy or prolonged rainfall, access to the wind-tidal flats was not possible. Ward and Berry (1972) describe capture methods. Hunt and Ward (1988) describe the study area. The survey accesses the wind-tidal flats behind the dune barrier and during autumn we monitor a route along the beachfront. Spring migrants rarely use the beachfront, so we do not survey the beach during the spring migration. Accessible landmass in the study area is greatly affected by tides, wind and rainfall. Total land area in the survey changes daily. All sightings and behavior of peregrine falcons and other raptors are noted. We have adopted the USFWS Bird Banding Laboratory (BBL) methods to describe age. Peregrine falcons in brown juvenile plumage and hatched in the same calendar year as their capture (autumn) are referred to as “hatching year” (HY). Observed birds that have completed at least one pre-basic molt and are in blue-gray plumage are designated “after hatching-year” (AHY). Peregrine falcons captured in the autumn that have completed a partial molt to adult feathers but still have juvenile feathers remaining are termed “second-year” (SY). Falcons returning to Padre Island in spring that were HY the previous autumn are designated SY. These individuals may or may not have begun molting into adult plumage. “After second-year” (ASY) refers to birds that have fully molted into adult plumage. The designation of AHY for observed birds may include SY birds, but an ASY notation does not (Ward et al. 1988).
Captured peregrine falcons are banded with
USFWS bands and a 2ml blood sample is taken from the brachiocephalic vein.
All birds are processed and released at the capture site, usually
within 5 minutes. The blood is
processed at the end of the day at the base station.
Red blood cells are separated from plasma by centrifugation and
stored in plastic tubes with an o-ring seal.
Each sample is then frozen. Red
blood cells can be used for genetic analyses at the protein or DNA level. Plasma is preserved for potential analysis
of environmental contaminants and for monitoring exposure to West Nile
Virus Starting
in autumn of 1988, the breast feathers of captured juvenile peregrine
falcons were marked with picric acid to reduce recapture during the same
season. We had not used dye prior to 1988, so that we could accumulate data
regarding staging time through the repeated capture of the same individual
during a survey period. Since
we now have extensive data documenting Padre Island as an important staging
area, our emphasis has been to band as many birds as possible. Even with marking, many birds are recaptured in the same season
and we continue to collect data concerning length of time spent in the
survey area. Because picric acid
is long lasting, we switched (in 1990) from using picric acid to Rhodamine
B. We found that Rhodamine B wore off the birds’
feathers in <2 weeks, depending on weather conditions. Adults and second-year birds are not dyed since
they are not frequently recaptured during the same season. Peregrines captured in spring are not dyed. Data regarding banding, age, sex, location, samples taken, and dates, from these surveys are maintained on a computer to facilitate access of recapture information. All banding information is reported to USGS/BRD Bird Banding Laboratory after each survey. RECOMMENDATIONS
The recovery of Arctic nesting peregrine
falcons is one of few success stories for endangered species.
While we supported delisting this species from the List of Threatened
and Endangered Species in 1994, we continue to recognize this species’
importance as an environmental indicator for not only migratory peregrine
populations, but also a myriad of other avian species.
Through the integration of several technologies, (e. g., tracking
of peregrines by satellite, analyses of genetic make-up and investigation
of contaminant burdens) the Padre Island survey can be used to monitor
the environmental health of a large geographic area. This includes diverse
habitats delimited by the movements of peregrines as revealed by satellite
derived location estimates. These
habitats are shared by a wide variety of avian species and can serve to
identify areas where further monitoring is warranted (particularly in
Latin America). We recommend that the
Padre Island Peregrine Falcon Survey be continued because data from our
research will: 1) provide information on population dynamics of migration;
2) provide samples to monitor for West Nile Virus, contaminant levels
and genetic composition; and, 3) help identify key migration and over-wintering
habitat of Neotropical migrants in the Gulf coast region and South America. Additionally, we recommend that winter use areas delimited through band returns and satellite received location estimates be investigated to evaluate their importance to peregrine falcons and other Neotropical migrants and resident species. SURVEY OBJECTIVES FOR 2004 Pending
sufficient funding, we plan to continue a spring survey in 2004 (5 April
through 5 May) and autumn 2004 (25 September through 25 October).
These surveys will be conducted using similar methods and number
of personnel as deployed during spring 2003. We
are collaborating with Dr. Sandra Talbot of USGS, in completing DNA level
analyses of peregrine samples acquired at Padre Island.
Talbot will utilize samples collected from past surveys and investigate
methods that will help us: 1) describe the composition of the
Dr. Nancy Clum of Depaul University, Chicago, Illinois
is leading research using feather samples collected from HY birds captured
at Padre Island to assess the feasibility of using stable isotopes as
a means of identifying natal origins of migrant birds.
These samples will be analyzed over the summer at Boston University’s
Stable Isotope Laboratory. If successful, this technique may allow us
to 1) evaluate the relative importance of different breeding habitats
to populations of arctic peregrines, 2) identify the dominant trophic
position of arctic peregrines, and 3) identify any temporal patterns of
migration related to breeding habitat.
Isotope data will be combined with data on plumage and morphological
variation, which have also been suggested to vary geographically among
peregrine populations. CONCLUSIONS Data from the Padre survey continue to suggest full recovery of Arctic populations of peregrine falcons. This conclusion is supported by reports of researchers observing increased production in most Arctic regions of North America (Cade et al. 1988). Henny et al. (1996) reported that organochlorine residues in plasma of peregrine falcons captured at Padre Island had decreased significantly in spring migrants at Padre Island between collections obtained during 1978, 1979, and 1980, with those collected in 1994. However, polychlorinated biphenyls (PCBs) were detected in 75% of birds sampled in 1994. Unfortunately the data sets collected in the late 1970’s and 1980 were not comparable (for PCBs) to those collected in 1994. Henny suggests that PCBs are accumulated in industrialized areas and may also reflect the diet preferences of individual peregrines. Henny noted that decreases in organochlorine pesticide residues coincided with increased peregrine populations throughout the Arctic and other regions of North America. While the decreased use of persistent organochlorines has been an important factor in restoring peregrine populations, it heralds a change in agricultural processes that may now employ less persistent but more toxic chemicals. ACKNOWLEDGEMENTS
We thank the following individuals for participating in the 2003 surveys: C.M. Anderson, John Dahlke, Gregg Doney, David Frank, Ken Franklin, William Ferrier, Christian Gonzalez, Willard Heck, Jim Ince, Paul Juergens, Brian Latta, Brian McDonald, Mark Proster, Scott Ward and Clayton White. Our research would not have been possible without grants from the Archie W. and Grace Berry Foundation, Grasslans Charitable Foundation and The Nature Conservancy. We extend our thanks to The Nature Conservancy for access to their property on the wind-tidal flats and for their support of this long-term study. Permits are appreciated from Texas Parks and Wildlife, and The Bird Banding Laboratory, Office of Migratory Bird Management. Laguna Atascosa National Wildlife Refuge Manager John Wallace, assistant manager Sonny Perez and the staff of Laguna Atascosa NWR continue to provide invaluable support with storage facilities for our equipment and the loan of a pick-up truck for the survey period. Robert McLean of USGS provided sampling supplies and analysis of serum samples for investigations into presence/absence of West Nile Virus. Richard Moore, Nature Reporter for KGBT-TV OF Harlingen, Texas helps to encourage conservation of Padre Island through reports about the survey on his nature show. Pete Moore provides local support and friendship on South Padre Island as well as providing observations of peregrines that winter there. Jim Dayton provided administrative support through Earthspan. The officers, board and donors of Earthspan continue to work tirelessly on behalf of the survey and for research of migratory peregrine populations. Our presence would not be possible without this continued support. LITERATURE CITED Cade, T. J., J. H. Enderson, C. G. Thelander, and
C. M. White (eds.). 1988. Enderson, J. H. 1963. A breeding and migration
survey of the Peregrine Enderson, J. H. 1969. Coastal migration data as
population indices for thePeregrine Falcon. pp. 275-278 in Peregrine Falcon
Populations: their Enderson, J. H., J. Larrabee, Z. Jones, Chris Peper,
and Chris Lepisto. 1995. Behavior of Peregrines in winter in South Texas.
J. Raptor Res. 29(2):93-98. Henny, C. J., K . E. Riddle, and C. S. Hulse. 1988.
Organochlorine Pollutants Henny, C. J., W. S. Seegar, and T. L. Maechtle.
1996. DDE decreases in plasma of spring migrant Peregrine
Falcons, 1978-1994. J. Wildl.
Manage. 60(2):342-349. Hunt, W. G., R. R. Rogers, and D. J. Slowe. 1975.
Migratory and foraging Hunt, W. G., and F. P. Ward. 1988. Habitat selection
by spring migrant Hunt, W. G., F. P. Ward, B. S. Johnson, C. M. Anderson,
and G. P. Vose. Longmire, J. L. 1988. Identification and development
of breeding Longmire, J. L., R. E. Ambrose, N. C. Brown, T.
J. Cade, T. L. Maechtle, W. S. Morizot, D. C. 1988. Biochemical genetic variability
in Peregrine Falcon Nisbet, I. C. 1988. The relative importance of
DDE and Dieldrin in the Parrish, J. R., D. T. Rogers, Jr., and F. P. Ward.
1983. Identification of natal Riddle, K. E., 1978 through 1985. Annual reports
to USFWS, Reg. 2; SAS Institute Inc. 1989. SAS/STAT User’s Guide,
Version 6, Fourth Edition, Volume 2, Cary, NC, 846 pp. Ward, F. P., and R. B. Berry. 1972. Autumn migrations
of Peregrine Ward, F. P., K. Titus, W. S. Seegar, M. A. Yates,
and M. R. Fuller. 1988. Weise, B. R., and W. A. White. 1980. Padre Island
National Seashore: a Yates, M. A., K. E. Riddle, and F. P. Ward. 1988.
Recoveries of Peregrine
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2)
capture and band as many individuals as possible; 3) sample blood from
captured individuals for DNA level genetic analyses; 4) maintain a bank
of blood serum for pesticide contamination analyses; 5) monitor for the
presence /absence of West Nile Virus through blood serum; 6) collect a
small feather sample from immature peregrines for stable isotope analysis,
and 7) identify migratory pathways and critical wintering areas as delimited
through the use of banding returns and locations of radio marked falcons
tracked by satellite.
migratory
population using a molecular probe that will identify birds to population
of natal origin; 2) assess the relative contribution of various breeding
populations to the migratory populations at Padre; 3) examine how changes
in weather patterns and migratory patterns influence the size of the migratory
populations, and 4) possibly draw conclusions about changes in the size
of breeding populations.