Comments on Frequency of Melanism in Myotis lucifugus

Abstract

Albino and leucistic Myotis lucifugus have been reported several times (Walley, 1974), but the only previous record of melanism in this species is one male (Amer. Mus. Nat. Hist. 139530) from Aitkin Cave in Mifflin County, Pennsylvania (Trapido and Crowe, 1942). On 15 January 1983, I found a black male M. I. lucifugus hibernating in a shallow crevice just beyond the photic zone in the adit of Craigmont Mine (Raglan Township, Renfrew Co., Ontario). The skin on the face, ears, wings, and uropatagium of this bat (ROM 88182) is black, whereas the skin beneath the fur is unpigmented. The dorsal fur, both underhair and overhair, is uniformly black from base to tip. The ventral fur is black with buffy tips, imparting a slight greyish wash to the belly. In contrast, most of the ca. 4,000 bats hibernating in Craigmont have darkish brown dorsal fur with a distinct coppery sheen and buffy grey ventral fur. Some individuals are paler. Comparison of this specimen with several hundred other study skins in the collection of the Royal Ontario Museum, representing most Nearctic and African Myotis, failed to reveal any examples that were comparably dark. An unusually dark female M. 1. lucifugus was collected on 13 March 1983 at Craigmont. This specimen (ROM 88393) has dark chocolate brown dorsal fur with coppery tips. The ventral fur is grey and slightly darker than in most Craigmont specimens. Coat color variation is widespread among mammals and is presumably adaptive, because it often correlates with age, habitat, or annual activity cycles. Melanism is common in most mammalian species, whereas erythrism (reddish or yellowish coat color) is uncommon (Searle, 1968). The situation in bats seems to be reversed. Erythristic variants have been noted in a number of species, but albinism is rare and melanism even rarer (Allen, 1939; Quay, 1970). The rarity of albinism is not surprising, because the alleles governing it are recessive, and albinism probably increases vulnerability of bats to predators (e.g., owls). However, the apparent rarity of melanism is curious. A number of gene loci can produce dark or black pelage, and melanism could be adaptive, or inconsequential, in nocturnal and cryptic animals. Melanism may be more common than the data indicate, because in the field an abnormally dark individual could easily escape notice. More importantly, variation from normal to melanic pelage is continuous and there are no objective criteria for assessing melanism. On the other hand, large-scale banding studies, widespread use of mist nets and bat traps in recent years, and extensive holdings in museum collections should have made detection of abnormal color variants easy. Nevertheless, except for the melanistic M. lucifugus reported by Trapido and Crowe (1942), and the black M. lucifugus described above, the only other report of melanism in North American bats is of three Pipistrellus subflavus captured near Rutland, Vermont (Osgood, 1936). I thank Dr. R. L. Peterson, Department of Mammalogy, Royal Ontario Museum, for confirming the identity of the specimens and permitting me to examine the study skins in the museum collection. The bats described in this paper were obtained during a study funded by MRC Grant MA-7618.