Balantiopteryx plicata Peters 1867

34. Gray Sac-winged Bat

Balantiopteryx plicata

French: Emballonura de Peters / German: Peters-Sackflügelfledermaus / Spanish: Embalonuro de sacos de Peters

Other common names: Peters's Sac-winged Bat

Taxonomy. Balantiopteryx plicata Peters, 1867,

Puntarenas, Costa Rica.

Two subspecies are recognized.

Subspecies and Distribution.

B. p. plicata Peters, 1867 - from C Sinaloa in Mexico to Nicaragua and NW Costa Rica.

B. p. pallida Burt, 1948 - confined to S Sonora, N Sinaloa, and the S tip of Baja California Sur states in Mexico.

Descriptive notes. Head—body 47—53 mm, tail 13—23 mm, ear 13-15 mm, hindfoot 7-10 mm, forearm 37-5-45-9 mm; weight 5-6 g. Based on forearm length, females (43-1 mm mean) are slightly larger than males (42-1 mm mean). Dorsal fur of the Gray Sac-winged Bat is smoky brown but often yellowish at base of tail membrane; venter is paler, with hairs faintly tipped bufiy brown along belly and flanks. Wings are brown-bordered, with white particularly between foot and fifth finger. Legs and forearms are pinkish. Wing sacs open toward body and do not extend to edges ofwings. Dental formula of the three species of Balantiopteryx is 11/3, C 1/1, P 2/2, M 3/3 (x 2) = 32.

Habitat. Deciduous forests, dry thorn scrub, and less commonly evergreen moist forests from sea level to elevations of c.1500 m.

Food and Feeding. The Gray Sac-winged Bat preys on aerial insects.

Breeding. Gray Sac-winged Bats are bom in May-July in Mexico and lateJune in Costa Rica, well after the start of rainy season. Females give birth to one young, apparently once a year.

Activity patterns. Gray Sac-winged Bats are crepuscular and roost in dim light near entrances of caves, mines, and tunnels; under overhanging large boulders; and in tree hollows and buildings including outdoor, shaded stairwells in close proximity to human foot traffic. Flight emergence begins a little before sunset, and individuals fly above canopies and forage with long, straight sallies and rapid dives to chase aerial insects. Early flight above relatively low, open canopies of deciduous forests can easily be observed. Calls with principle energy in second harmonic, start with 42- kHz narrowband component that drops slightly by 1-1-5 kHz at 39-kHz broadband. Mean call duration is 12 milliseconds. Terminal drop in frequency over a broadband facilitates targeting approaches to flying insects, and relatively long call duration is indicative of foraging in open areas rather than close to vegetation.

Movements, Home range and Social organization. Groups of Gray Sac-winged Bats often gather in night roosts central to foraging areas, including under bridges. Group size is usually greater than 50 individuals, and male—female sex ratio is c.3:1. When approached, Gray Sac-winged Bats lay their ears back, like a dog, and back away deeper into the roost.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Gray Sac-winged Bat has a large distribution and presumably large and relatively stable population, and it occurs in protected areas. Threats include habitat loss and vandalism and fire caused by humans in roost caves.

Bibliography. Arroyo-Cabrales & Jones (1988a), Bradbury & Vehrencamp (1976 a, 1976b), Burt (1948), Hood & Gardner (2008), Ibänez et al. (2002), Lopez-Forment (1976), Reid (2009), Solari et al. (2013), Villa (1967).