Mensural Discrimination of Peromyscus 117 



the test specimens, and results should be viewed with caution if that 

 model is used for specimens collected far outside the geographic distribution 

 of our samples. 



Our results were similar to those of previous authors who found 

 that these species tend to differ significantly in most measurements, 

 but that there is generally some overlap in measurement that prevents 

 classification of some specimens based on single characters. For example, 

 Linzey et al. (1976) could separate most specimens using anterior 

 palatal foramen length and width or skull length. Choate (1973) could 

 separate most specimens with tail length. Engstrom et al. (1982) found 

 that P. gossypinus differed significantly from P. leucopus in every 

 character they measured, but that there was overlap in all characters. 

 McCarley (1954) found that hindfoot length separated most P. leucopus 

 from P. gossypinus. 



Stromberg (1979) successfully used discriminant analysis on external 

 characters to separate P. maniculatus from P. leucopus. We found 

 that these characters could not be used in the extreme Southeast (Fig. 

 2). However, he found that ear length was especially useful, and we 

 were not able to include that character. We disagree with Stromberg's 

 (1979) statement that discrimination of external characters offers a 

 dependable alternative to cranial measurements in the identification 

 of P. maniculatus and P. leucopus. As in our study, McDaniel et al. 

 (1983) and Choate et al. (1979) were able to separate almost all of 

 their specimens using cranial measurements. Only Engstrom et al. 

 (1982) was able to separate all of their specimens using cranial measurements. 



Choate (1973), Choate et al. (1978), and Engstrom et al. (1982) 

 found that variation among adult age classes was required in the 

 models for accurate classification. In contrast, we did not find that 

 age variation among adult age classes (4-6, Schmidly 1973) was significant. 

 We found statistical differences among age classes 4-6, but these 

 differences were small relative to the differences among species, and 

 thus age information was not important in our models. 



Several authors have found ratios useful in identifying Peromyscus 

 species pairs. McDaniel et al. (1983) found that the ratio of interorbital 

 width to length of the nasal bone was useful in separating P. attwateri 

 from P. gossypinus. Feldhamer et al. (1983) found that the ratio of 

 tail length to body length in conjunction with body mass separated P. 

 leucopus from P. maniculatus (pregnant females excluded). McCarley 

 (1954) used the ratio of skull length to foot length to identify P. 

 gossypinus, P. leucopus, and their purported hybrids. Although ratios 

 may provide useful indices, we agree with Humphries et al. (1981) 

 and the references they provide that ratios should be avoided in morphometric 



