Artibeus (Dermanura) gnomus Handley

Figures 41, 42

VOUCHER MATERIAL: 18 females (AMNH *266195, *266239, *266301, *266303, *266308, *266309, *266310, *267199, *267979, *267988, *267989; MNHN *1995.1124, *1995.1125, *1995.1126, *1995.1127, *1995.1128, *1995.1129, *1995.1130) and 24 males (AMNH *266304, *266314, *266316, *266317, *266318, *267200, *267984, *267985, *267986, *267987, *267990, *267992, *267993, *267994, *267995, *267996; MNHN *1995.1131, *1995.1132, *1995.1133, *1995.1134, *1995.1135, *1995.1136, *1995.1137, *1995.1138); see table 39 for measurements.

IDENTIFICATION: The original description of Artibeus gnomus by Handley (1987) is still the basic reference for this species, although the measurements tabulated by Brosset and Charles­Dominique (1990) for their French Guianan material are also helpful. The few problems we encountered in distinguishing A. gnomus from A. cinereus were discussed in the preceeding species account. No subspecies of Artibeus gnomus are recognized (Handley, 1987).

Our voucher material corresponds closely with Handley’s (1987) description of Artibeus gnomus, and measurements of our specimens generally fall within the range of variation previously reported for the species. One exception is a particularly large male (AMNH 267987), whose measurements in several dimensions exceed any previously reported in the literature (e.g., length of maxillary toothrow, 6.08 mm; breadth across molars, 8.30 mm; zygomatic breadth, 11.47 mm). Except in size, however, this specimen agrees morphologically with the remainder of our specimens, and we conclude that it simply represents an unusually large example. Unpublished measurement data from other localities (in Venezuela, Guyana, Peru, and Brazil; Handley, personal commun.) indicate that AMNH 267987 is not unique in this respect, and that the normal range of size variation in A. gnomus is somewhat greater than that originally reported by Handley (1987).

FIELD OBSERVATIONS: We recorded 59 captures (possibly including some recaptures) of Artibeus gnomus at Paracou: 51 in groundlevel mistnets, 4 in elevated mistnets, and another 4 at roosts. Of the 51 ground­level mistnet captures, 6 were in well­drained primary forest, 17 were in swampy primary forest, 5 were in creekside primary forest, 22 were in manmade clearings, and 1 was in closed­canopy secondary growth. It is noteworthy that of the 22 ground­level mistnet captures in manmade clearings, 18 were taken in nets erected around small fruiting trees, Vismia sp. (Clusiaceae), growing along a narrow road through well­drained primary forest; none were made in large clearings far removed from primary forest. Of the elevat­ ed mistnet captures, two were made between 4 and 21 m above a narrow dirt road and two were made at 7–10 m in the subcanopy of swampy primary forest.

We found four roosting groups of Artibeus gnomus, all of which occupied leaf­tents. Two large roosting groups (one with 4–8 individuals, the other with perhaps 6–10) each inhabited a single modified leaf of the giant herb Phenakospermum guyannense (Strelitziaceae); both roosts were hard to see, about 3 m above the ground in the densely cluttered understory of swampy primary forest (fig. 46). We captured (and preserved as vouchers) only a single adult female from each of these roosting groups, the age and sex composition of which are otherwise unknown.

The other two roosts, inhabited by solitary adult males, were ‘‘apical’’ tents (sensu Kunz et al., 1994) made from the spade­shaped leaves of epiphytic Philodendron sp. (Araceae). One of these roosts was about 5 m above the ground in well­drained disturbed forest, the other about 10 m above the ground in well­drained primary forest. We found many epiphytic Philodendron plants with similarly modified leaves throughout our study area, but only these two examples were occupied by bats (wasp nests were found under the modified leaves of a few plants).

Although Artibeus gnomus and A. cinereus are morphologically similar, our data suggest they are ecologically divergent. Consistent with Brosset and Charles­Dominique’s (1990) generalizations concerning habitat use in these species, an analysis of ground­level capture frequency data from Paracou (table 40) suggests that A. gnomus is more abundant in primary forest than A. cinereus, which apparently favors the early­successional vegetation of modified habitats. Whether or not A. cinereus consistently inhabits bifid palm­leaf tents whereas A. gnomus uses differently designed tents made from the leaves of large herbs is unknown, but this hypothetical difference could easily be tested by following the movements of positively identified bats fitted with radio transmitters. Because A. gnomus was only recently recognized as taxonomically distinct from A. cinereus, and because they are hard (but not impossible) to distinguish in the field, unvouchered ecological observations reported in the literature for these species should be regarded with caution.