Evaluation of call-response surveys for monitoring breeding Yuma Clapper Rails (Rallus longirostris yumanensis)

During March-June 2000 we evaluated the use of call-response surveys to monitor breeding Yuma Clapper Rails (Rallus longirostris yumanensis) at the Ciénega de Santa Clara, Colorado River Delta, Sonora, Mexico. We assessed the effect that time of day, stage of breeding season, and number of survey periods had on the average number of rails detected at a station. Conducting call-response surveys resulted in a significant increase in the number of detected rails and reduced the coefficient of variation of the average number or rails per station, which increases the statistical power to detect population trends. Using this technique also appears to reduce the variation of rates of responses by rails through the breeding season when compared to passive listening. There was no difference between the number of rails detected during morning and afternoon surveys. The established protocol developed by the U.S. Fish and Wildlife Service for Yuma Clapper Rail surveys is adequate for monitoring, and it should continue to be implemented on a yearly basis at the Ciénega de Santa Clara and other wetlands of the Colorado River Delta in Mexico.