Abundance, distribution, and habitat use of Yuma clapper rails (Rallus longirostris yumanensis) in the Colorado River Delta,Mexico

Abstract

I conducted call-response surveys for Yuma clapper rails in the Colorado River delta, Mexico during the breeding seasons of 1999 and 2000 to estimate abundance, determine distribution, and identify patterns of habitat use. The maximum estimate of abundance was 6,629 individuals (95% C.I. 4,859 to 8,399). Rails were widely distributed in the delta, occupying almost all marshlands dominated by cattail. Rail density was higher in the Cienega de Santa Clara than in the other wetlands of the delta. High densities of clapper rails were associated with increased water depth, high cattail coverage, high vegetation coverage, low saltcedar coverage, proximity to shoreline, and increased salinity up to 8 ppt. As this is an endangered subspecies shared by Mexico and the U.S., the conservation of the delta ecosystem should be the interest of both countries, especially when management decisions upstream in the U.S. have an impact over natural areas downstream in Mexico.