Micronycteris megalotis (Gray)

Simmons, Nancy B. & Voss, Robert S., 1998, The mammals of Paracou, French Guiana, a Neotropical lowland rainforest fauna. Part 1, Bats, Bulletin of the American Museum of Natural History 237, pp. 1-219 : 75-76

Micronycteris megalotis (Gray)

VOUCHER MATERIAL: 4 females (AMNH *267092, *267862; MNHN *1995.809, *1995.811) and 7 males (AMNH *266020, *267090, *267091, 267863; MNHN *1995.803, *1995.804, 1995.810); see table 24 for measurements.

IDENTIFICATION: Characters distinguishing Micronycteris megalotis from other congeneric species were summarized under the species account for M. brosseti (above); additional diagnostic information can be found in Simmons (1996b). Comparative measurements of megalotis from the Guianas can be found in Husson (1962, 1978) and Brosset and Charles­Dominique (1990). Many previous accounts of megalotis (e.g., Sanborn, 1949; Swanepoel and Genoways, 1979; Hall, 1981; Koopman, 1994) treated microtis as a subspecies, so such references must be used with care. No subspecies of M. megalotis are presently recognized (Simmons, 1996b).

Handley (1976) reported that Micronycteris megalotis and M. microtis occur sympatrically in Venezuela, but Brosset and Charles­Dominique (1990) were the first authors to discuss diagnostic characters. They noted that, although the dentition is similar in megalotis and microtis , these species can be distinguished easily on the basis of ear length (longer in megalotis ). According to Brosset and Charles­Dominique, the palate is also slightly longer and wider and the braincase is slightly higher in megalotis than in microtis . Palatal shape differences were attributed by these authors to differences in length and width of the maxillary toothrow, although the measurements they reported indicated species overlap in both dimensions. In addition to ear and craniodental differences, Brosset and Charles­Dominique (1990: 522) observed that ‘‘the ventral surface of megalotis is lighter than the dorsal surface, but this is not the case for microtis , which is grey brown above and below.’’

Simmons (1996b) agreed that Micronycteris megalotis and M. microtis are distinct species based on her examination of specimens from Paracou and elsewhere. She found that ear length is indeed different in these species although some overlap in measurements is apparent when the smallest specimens of megalotis are compared with the largest specimens of microtis . No consistent differences in craniodental measurements or fur color were found when large samples of megalotis and microtis from many different localities were compared. However, Simmons identified one obvious difference between these species: the length of the hair on the leading edge of the pinna is relatively long (7–8 mm) in megalotis but is much shorter (≤ 3 mm) in microtis .

Our comparisons of specimens of Micronycteris megalotis and M. microtis collected at Paracou indicate that several features distinguish these species where they occur sympatrically in French Guiana: (1) length of dorsal fur over the upper back (long in megalotis [8–11 mm], shorter in microtis [7–8 mm]), (2) color of the dorsal and ventral fur (dark gray­brown in microtis , more reddish in megalotis ), (3) length of the fur on the outside of the medial third of the ear pinna (long in megalotis [7–8 mm], much shorter in microtis [≤ 3 mm]), (4) ear length (greater in megalotis [22–23 mm], shorter in microtis [19–21 mm]), and (5) maxillary toothrow length (males only; long in megalotis [6.90– 7.15 mm], shorter in microtis [6.45–6.75 mm]). We found overlap in all other external and craniodental measurements although mean values for megalotis are somewhat larger than mean values for microtis for several dimensions (e.g., greatest length of skull, condyloincisive length; table 24).

Contra Brosset and Charles­Dominique (1990), we did not find that the ventral fur is noticeably paler than the dorsal fur in megalotis . In our experience, dorsal and ventral fur is approximately the same color in all individuals of both megalotis and microtis . However, the reddish fur of megalotis appears lighter in contrast to the dark wing membranes than does the gray­brown ventral fur of microtis . The differences in fur color in megalotis and microtis that we observed at Paracou are subtle and not discernable in wet specimens. These differences may also be obscured by bleaching in older material, possibly the reason for Simmons’ (1996b) previous inability to distinguish consistent pelage color contrasts between megalotis and microtis in her preliminary survey of specimens collected at different times and places. Alternatively, the differences we observed at Paracou might be geographically variable.

FIELD OBSERVATIONS: We captured 11 Micronycteris megalotis at Paracou, of which 8 were taken in ground­level mistnets (1 in well­drained primary forest and 7 in swampy primary forest) and the other 3 at a roost. The single roost we found was in the central cavity of a large buttressed tree growing in welldrained primary forest (fig. 25). The roosting group consisted of four bats hanging together in a tight cluster from the roof of the cavernous lower chamber about 2.5 m above the ground; two adult males and one adult female were captured and one bat escaped. A solitary adult male Carollia perspicillata was simultaneously found roosting in the same chamber.