Population Studies of Wilson's Phalaropes at Fall Staging Areas, 1980-1997: A Challenge for Monitoring

Abstract

-The great majority of adult Wilson's Phalaropes (Phalaropus tricolor) is thought to stage at Great Salt Lake, Utah, Mono Lake, California, and/or Lake Abert, Oregon, before making a nonstop flight to South America. Their concentration at a few localities provides an exceptional opportunity for studying trends species-wide, so long as several important assumptions are fulfilled. Observations from 1980 through 1997 indicated that numbers of staging adults approximated 500,000-600,000 in thel980s, then dropped by about half in the 1990s. Data from the breeding grounds in 1967-1992, including Breeding Bird Surveys, also indicated a general decline had been in progress, but did not indicate any sudden recent changes. The validity and severity of the decline is hard to test because correspondence between population sizes predicted from BBS trends and observations from staging areas is poor. Difficulties in gathering and interpreting data from a species that is easy to study raises questions about our ability to monitor and understand population trends in less amenable species. Whether population fluctuations in Wilson's Phalaropes are related to the availability of habitat in the main breeding range requires confirmation. Received 8January 1999, accepted 13January 1999.