Field identification of two morphologically similar bats, Miniopterus schreibersii natalensis and Miniopterus fraterculus (Chiroptera: Vespertilionidae)

Miniopterus schreibersii natalensis and Miniopterus fraterculus are two morphologically similar, but genetically distinct, species of insectivorous bat that, more often than not, share roosts. Identifying these two species in the field is difficult because of an overlap in the ranges of both forearm and mass. We thus attempted to find morphological features that could be used to distinguish between these two species in the field. We compared cranial and external morphological measurements from museum specimens of the two species, using principal component analysis and discriminant function analysis, to determine which variables could be used to discriminate between them. Length of the hind foot and total body length were identified as the variables responsible for most of the variation between these two species. Miniopterus s. natalensis has a longer total body length (113.6 ± 3.5 mm) than M. fraterculus (102.2 ± 4.8 mm) but a relatively shorter hind foot (9.1 ± 0.6 mm, 9.8 ± 0.8 mm, respectively). A function generated from standardized canonical variables, (HF × 0.279417) - (TL × 0.989306) + 100, and based on length of hind foot (HF) and total body length (TL) generated function scores <0 for M. s. natalensis and >0 for M. fraterculus. On the basis that positive values (above zero) indicated M. fraterculus, and negative values (below zero) indicated M. s. natalensis, we were able to correctly assign 20 individuals to their respective species using the above function. These individuals were previously identified as M. fraterculus or M. s. natalensis from their mtDNA sequences. The function thus provides a useful tool for discriminating between the two species in the field.