Project- Swainson's Hawk

Scientific Research Rescues Swainson’s Hawk Before
Threatened Or Endangered Status Listing Is Needed

Problem/Background

The Swainson’s Hawk (Buteo swainsoni), once a very abundant breeder in the western United States, has declined in numbers and distribution in the last few decades and is now listed as a species of concern by five states and the Bureau of Land Management, and as a special emphasis species by the U.S. Forest Service.  Nesting population declines had been reported over much of the Swainson's Hawk's range in the early 1990s. With no obvious reason for this decline, scientists hypothesized that problems along migration routes or on wintering areas were responsible.  It was therefore critical for scientists to find out exactly where the birds spend the winter and where they stop over during migration, in order for them to investigate the possible causes for their decline. 

Objectives/Methods

Thirty Swainson’s Hawks were captured and tagged with satellite transmitters during July, August, and September, 1996, in 8 locales within the western United States and Canada, includingCalifornia (1), Colorado (3), Idaho (6), Minnesota (2), Oregon (6), Utah (3), Arizona (2), Saskatchewan or Alberta, and Canada (7).  Birds typically departed from nesting areas in middle to late September and arrived in Argentina beginning in the second week of November.  By late November, 25 of the 30 Swainson’s Hawks had crossed the Argentinean border and by mid-December had settled into the Pampas region of central Argentina (See Map Below). 
      In January of 1996, scientists used the satellite tracking data to visit different areas where the birds were spending the winter.  When the scientists arrived  at these areas, they counted over 4,000 dead Swainson's Hawks!  These scientists believed the actual mortality numbers might have been greater than 20,000 birds; this loss represented a serious threat to the survival of the species.  The scientists noticed that in the areas where these birds were found dead, farmers were spraying their crops with a new pesticide to control grasshopper outbreaks.  The scientists hypothesized that the hawks were getting poisoned from eating the grasshoppers (who eat the sprayed crops) or from direct exposure to the poison.  Biologists in Argentina gathered blood samples for chemical analyses to determine if the hawks had the poison in their blood.  They also attempted to gather behavioral data to relate the hawks' behavior and ecology to land uses, environmental contaminants, and other threats.

Results/Conclusion

It turned out that this catastrophic population decline resulted from the use of a toxic organophosphate pesticide, recently brought into use on the Pampas of Argentina where these hawks spend the winter in communal roosts.  The pesticide doesn't stay in a bird's bloodstream for very long, so if a bird is exposed to the pesticide and survives, scientists would never be able to detect that the bird was exposed to the poison.  This is why birds that were tested for pesticide exposure on their breeding grounds didn't show any traces of pesticides in their bloodstream.  It was only because scientists were able to track down their locations on their wintering grounds using satellite telemetry that they were able to discover the cause of the huge declines in their population.
      Through the collaboration of scientists, resource managers, the Argentinean government, and educators, the use of this pesticide in Argentina was stopped within 18 months of this study.  In response, the Swaison's Hawk populations are no longer declining at such an alarming rate.  The scientists managed to keep this raptor off the endangered species list.  This also saved the United States government millions of dollars by avoiding costly, large-scale research and recovery programs and related habitat management activities in North America, which would have been necessary if the hawks became listed as an endangered species.  This application of wildlife tracking via satellite is a perfect demonstration of the unique advantage this technology can provide in the study of a wide-ranging species.