Morphometric Characterization of the Grasshopper Sparrow (<i>Ammodramus savannarum</i>) and Baird’s Sparrow (<i>Ammodramus bairdii</i>) during the Wintering Season

Abstract

Grassland bird populations have declined more than any other group of bird species in North America. Some species such as the grasshopper ( Ammodramus savannarum ) and Baird’s sparrows ( Ammodramus bairdii ) are of particular conservation concern, since they have shown negative trends in their population over the last 50 years. Their winter ecology has only begun to be studied recently and information is limited. The purpose of this study is to achieve the morphometric characterization of these two grassland species during the wintering season. The study is conducted in the Rancho Santa Teresa located in Villa Hidalgo, Durango, Mexico and the Ecological reserve “El Uno”, located in Janos, Chihuahua, Mexico. During winter 2013-2014, 135 birds were captured; banded and zoometric measurements were taken such as total body weight, wing chord, tail length, culmen, and beak depth and width. Two indices of body condition (BCI) are also calculated. All measurements and indices are compared per species and per sex. Both species are sexed with molecular techniques, determining 20 females and 18 males for A. bairdii and 41 females and 56 males for A. savannarum . All variables are significant different between species ( p < 0.05). Beak measurements are not significantly different when comparing birds of different sexes (same species), with the exception of beak width of A. bairdii ( p < 0.05). Male’s weight, wing chord, tail length, as well as one of the body condition indices (BCI2) are significantly higher ( p < 0.05) than females’ for both species. BCI1 shows significant differences ( p < 0.05) between species and sexes in A. bairdii . The biometric data obtained in this study can be used as reference values wintering populations of both species.