204.

Van Gelder’s Bat

Bauerus dubiaquercus

French: Antrozon de Van Gelder / German: Van-GelderFledermaus / Spanish: Antrozo de Van Gelder

Taxonomy. Antrozous (Bauerus) dubiaquercus Van Gelder, 1959,

“Maria Magdalena Island, Tres Marias Islands, Nayarit, Mex-10.”

Originally described in monotypic subgenus Bauerus; on morphological grounds this was later raised to genus level. Monotypic.

Distribution. Disjunct distribution in WC Mexico (Jalisco and Marias Is) and S Mexico (Veracruz E to Yucatan Peninsula) S to Guatemala, Belize, and N Honduras; also known from El Salvador, N Nicaragua, and Costa Rica.

Descriptive notes. Head-body 55-78 mm, tail 43-57 mm, ear 20-27 mm, hindfoot 11-14 mm, forearm 50-2-57 mm; weight 18-25 g. Females generally larger than males. Fur long, soft and silky (dorsal hairs ¢. 9 mm long); dorsally bicolored, with dark brown bases, and medium brown to cinnamon-brown tips, with weak contrast between bases and tips; ventrally bicolored, with dark brown bases, and medium brown to yellowish or pale grayish tips, with strong contrast between bases and tips. Bats from Marias Islands are lighter than those of mainland. Ears large, extending well beyond muzzle when laid forward. Membranes are blackish; plagiopatagium is broadly attached to foot at level of base of toes. Baculum has long axistilted upward so that distal end lies closer to dorsal surface than proximal end. Skull is large (greatest skull length 19-2-21-5 mm); sagittal crest pronounced, continuous, and extended posteriorly as inion; rostrum elevated and broad. Auditory bullae very small and narrow, exposing more than one-half of overlying cochleae; bullae attenuated anteriorly. Mandible angled strongly upward posteriorly; angular process projects almost horizontally; upper tooth row is anteriorly convergent; talonid of M, roughly equal in length to trigonid; two or three lower incisors present; lower incisors are crowed. Dental formulais11/2-3,C1/1,P1/2,M 3/3 (x2) = 28-30. Chromosomal complement has 2n = 44 and FN = 52, with two large, one medium-sized, and two small metacentric pairs of chromosomes, a graded series of 16 medium-sized to small acrocentric, a medium-sized submetacentric X-chromosome, and a small acrocentric Y-chromosome.

Habitat. Wide variety of tropical forest habitats, such as lowland, pre-montane and montane evergreen rainforest, moist montane pine-oak forest, and lowland tropical deciduousforests, at elevations of 100-2300 m (commoner below 1300 m).

Food and Feeding. Insectivorous, foraging within forested areas and over water. Morphology suggests it captures insects exclusively in flight. No specific data on diet.

Breeding. In April, a pregnant female with one embryo (22 mm in crown-rump length) was caught in Honduras, and in the same month, a lactating female was caught in Chiapas, southern Mexico. Post-lactating females were collected in July in Costa Rica.

Activity patterns. Nocturnal, emerging shortly after sunset. Data of radio-tagged bats in Belize indicate that only short flights are made at 18:00-00:00 h. In Belize, the species was found sheltering in hollow of Swartzia cubensis tree ( Fabaceae). Echolocation calls are very short, broadband, and multiharmonic; peak harmonic is the fundamental. Call means are: maximum frequency 61-6 kHz, minimum frequency 27-4 kHz, peak frequency 36-3 kHz, bandwidth 34-6 kHz, and call duration 3-2 milliseconds.

Movements, Home range and Social organization. No information.

Status and Conservation. Classified as Near Threatened on The IUCN Red List. Although still widely distributed,it is locally uncommon, dependent upon highly fragile habitats, and is in significant decline (but at a rate of less than 30% over 15 years) due to human population density and habitat conversion.

Bibliography. Engstrom & Wilson (1981), Engstrom et al. (1987), Fenton et al. (2001), Gir6n et al. (2010), Martin & Schmidly (1982), O'Farrell & Miller (1999), Pine (1966), Pine et al. (1971), Simmons (2005), Solari (2018j), Van Gelder (1959), Wilson (1991).