Michael L. Casazza John Y. Takekawa Tobias M. Rohmer Cory T. Overton 2009 <p>California Clapper Rails (Rallus longirostris obsoletus) have monomorphic plumage, a trait that makes identification of sex difficult without extensive behavioral observation or genetic testing. Using 31 Clapper Rails (22 females, 9 males), caught in south San Francisco Bay, CA, and using easily measurable morphological characteristics, we developed a discriminant function to distinguish sex. We then validated this function on 33 additional rails. Seven morphological measurements were considered, resulting in three which were selected in the discriminate function: culmen length, tarsometatarsus length, and flat wing length. We had no classification errors for the development or testing datasets either with resubstitution or cross-validation procedures. Male California Clapper Rails were 6-22% larger than females for individual morphological traits, and the largest difference was in body mass. &nbsp;Variables in our discriminant function closely match variables developed for sexing Clapper Rails of Gulf Coast populations.&nbsp;However, a universal discriminant function to sex all Clapper Rail subspecies is not likely because of large and inconsistent differences in morphological traits among subspecies.&nbsp;</p> application/pdf en North American Bird Bander Sexing California Clapper Rails using morphological measurements article