SEASONAL-CHANGES IN YUMA CLAPPER RAIL VOCALIZATION RATE AND HABITAT USE

Yuma clapper rails (Rallus longirostris yumanensis) are protected unde r the Endangered Species Act, and 90% of the U.S. population occurs wi thin 2 wetland complexes. Assessment of impacts on, and mitigation mea sures for, Yuma clapper rails are required by law, yet managers lack q uantitative information on habitat requirements. Seasonal habitat requ irements provide resource managers with the information necessary to a ssess effects of development and water use practices on Yuma clapper r ails in the Southwest. Playback recordings are commonly used to survey rail populations, yet their accuracy has not been evaluated. Conseque ntly, we examined survey techniques and seasonal habitat requirements of Yuma clapper rails during 1985-87 on the lower Colorado River in so uthwestern Arizona to provide the recovery team and resource managers with reliable population estimates and habitat requirements. Response rates of radio-marked birds to playback recordings were highest (P < 0 .001) in April-May (40%), then decreased drastically. Most birds did n ot respond to playback recordings. Habitat use by Yuma clapper rails c hanged seasonally, reflecting different nesting and foraging habitat r equirements. Rails used complex marsh environments with areas of high water coverage, low stem densities, and moderate water depths for fora ging and areas with shallower water for nesting. Low stem densities an d little residual vegetation were considered year-round requisites of Yuma clapper rail habitat and habitat discrimination was greatest duri ng early winter. Birds moved greater (P < 0.05) distances and used lar ger (P < 0.05) areas during winter. Our results suggest that future ma nagement plans, recovery efforts, assessment of impacts, and mitigatio n measures for Yuma clapper rails should stress winter habitat needs. We recommend active manipulation of marshlands on a 4- to 5-year cycle to ensure a complex mosaic of patchily distributed environments more similar to historic conditions along the Colorado River.