Spotted bat (Euderma maculatum) COSEWIC assessment and status report: chapter 3

Species Information

Name and classification

The Spotted Bat, Euderma maculatum, (J.A. Allen 1891) belongs to the Order Chiroptera, Family Vespertilionidae, tribe Plecotini. First described and named as Histiotus maculatus by Allen (1891), this taxon was subsequently classified as Euderma maculatum by Allen (1892). E. maculatum is most closely related to Allen's big-eared bat (Idioncyteris phylottis). Taxonomists have generally considered these two taxa to be genetically distinct. However, a cladistic analysis of morphological and karyotypic characters led Frost and Timm (1992) to conclude that the genus Idionycteris should be synonymized with the genus Euderma. Another cladistic study (Tumlinson and Douglas 1992) using morphological traits concluded that the two taxa are highly derived and warrant treatment as separate genera. An analysis of mitochondrial DNA by Hoofer and van den Bussche (2001) demonstrated a sequence divergence between Idionycteris and Euderma of 16.9%, a difference consistent with genetic distinction. No subspecies are recognized in E. maculatum.

Another English common name for E. maculatum is the pinto bat. The French common name is Oreillard maculé.

Description

The most distinctive bat in Canada, the Spotted Bat has jet black fur that contrasts with prominent white spots on the rump and shoulders (Figure 1). Smaller white patches occur at the base of the ears; the undersides are whitish with black underfur. The enormous pinkish-grey ears are connected at their base across the forehead. A bare area about 7 to 10 mm in diameter is present on the throat. The wing and tail membranes are pinkish-red. Distinctive features of the skull include an elongated braincase and elliptical shaped auditory bullae (van Zyll de Jong 1985). The dental formula is: incisors 2/3, canines 1/1, premolars 2/2, molars 3/3.

Figure 1. Dorsal view of Spotted bat (Euderma maculatum). Photo M.B. Fenton.

Figure 1. Dorsal view of Spotted bat (Euderma maculatum)

There has been considerable speculation on the adaptive significance of the striking markings on this bat that resemble the ‘death-mask’ markings found on some invertebrates. Easterla (1965) suggested that the pelage colour and markings were cryptic providing camouflage for roosting Spotted Bats against black rocks with white crystalline patches. Given the wide range and colour of rock types used as roosts, selection for camouflage seems unlikely. Other explanations include aposematic markings or a visual signal for communicating with conspecifics (van Zyll de Jong 1985).

Body measurements (range in parentheses) for the few captures and single museum specimen from the Canadian population are: ear length 39 mm, n=1, tragus 14 mm n=1, forearm length 51.2 mm (47.9-53.1) n=6, and body mass 17.9 g (16.2-21.4) n=5 (Nagorsen 2002). Of 16 cranial and external measurements analyzed by Best (1988), only forearm length showed significant sexual dimorphism with females larger than males. A mutivariate analysis of the 16 measurements revealed significant geographic variation across the range with Spotted Bats from the northern United States and Canada smaller than specimens from the southern United States and Mexico (Best 1988).

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