An isolated population of the secretive, endemic Aztec Rail (Rallus tenuirostris) in Chihuahua, Mexico

Abstract

Here, we report new distributional information of the Aztec Rail (Rallus tenuirostris), a Mexican endemic that inhabits freshwater marshes throughout the highlands of central Mexico. We found an unidentified rail population during opportunistic area-search surveys between February and May in 2016 and 2017 along the San Pedro and Conchos rivers in Chihuahua, Mexico. Given the high phenotypic similarity between some North American Rallus taxa, we sequenced the mDNA marker ND2 of a specimen and performed a phylogenetic analysis, which allowed unequivocal identification. Maximum likelihood analysis placed the Chihuahuan sample within a clade grouping Aztec Rail samples from central Mexico. We also performed species distribution modeling (SDM) to assess habitat suitability of the newly identified Chihuahuan population of the Aztec Rail, which would account for its possible year-round permanence in the area. SDM results suggest that the Conchos River has the highest habitat suitability, followed by San Francisco del Mezquital. The environmental variables that mostly contributed to SDM were standard deviation of the enhanced vegetation index, annual mean temperature, and precipitation seasonality. The apparently small population of the Aztec Rail in Chihuahua may be either the result of recent dispersals from its core range in central Mexico, or a relict population from a formerly larger distributional range; further studies are needed to clarify this issue.