Sac-winged bats, sheath-tailed bats, and ghost bats

(Emballonuridae)

Class: Mammalia

Order: Chiroptera

Suborder: Microchiroptera

Family: Emballonuridae

Thumbnail description
Small, insect-feeding bats with mostly brown or gray fur and relatively large eyes; many emballonurid bats roost at almost vertical substrates with the folded forearms supporting the body

Size
Head and body length: 1.4–6.3 in (36–160 mm); forearm: 1.4–3.9 in (36–100 mm); weight:0.1–3.5 oz (3–100 g)

Number of genera, species
12 genera, 47 species

Habitat
Daytime roosts in well-lit portions of hollow trees, buttress cavities, rock shelters, or caves. Foraging habitats in evergreen forests, semideciduous forests, or savannas

Conservation status
Critically Endangered: 2 species; Endangered: 2 species; Vulnerable: 10 species; Lower Risk/Near Threatened: 7 species

Distribution
In tropical and subtropical regions from Mexico to Argentina in the New World. In the Old World in Africa, Madagascar, the Indian subcontinent, and Southeast Asia to Australasia

Evolution and systematics

Emballonurid bats are first recorded in Europe from the middle Eocene to early Miocene, in Africa from early Miocene to Recent, in South and Central America from Pleistocene to Recent, and in other areas of their geographical range from Recent. Two subfamilies are distinguished: Taphozoinae and Emballonurinae. Some authors consider the genera Diclidurus and Cyttarops as a separate subfamily Diclidurinae.

Physical characteristics

Emballonurid bats are small bats with relatively large eyes. The ears have a tragus and, in some species, the ears are connected. Males of some New World species (sac-winged bats) have a sac-like organ in the frontal wing membrane that contains a strong smelling liquid. Females have only rudiments of this organ and it is not known if females use it in a behavioral context. Position and size of these sacs vary among species. The ghost bats, genus Diclidurus, have a sac-like organ in the wing-tail membrane. These bats are also an exception within the whole family as they have white fur. Within the genus Taphozous, some members possess a gland at the chest. In general, emballonurid bats have grayish to brown fur. The tail emerges free through the tail membrane and projects above its dorsal surface.

Distribution

The family Emballonuridae occurs both in the New World and in the Old World. There are 18 species in the New World with a distribution range from southern Mexico to northern Argentina. The 29 species of the Old World inhabit Africa, the Indian subcontinent, and Southeast Asia to Australasia. Most species are restricted to the lowland regions. The species diversity of emballonurid bats increases towards the equator.

Habitat

Emballonurid bats inhabit humid rainforests, seasonal semi-deciduous forests, and savannas. Most species roost in well-lit places like entries to caves and temples, at the outside of buildings, or in hollow trees and buttress cavities of large trees.

Behavior

Colonies of some emballonurid species are easily found because these bats emit social calls audible to humans. The roosting posture of emballonurid bats is characteristic as they support their body from the surface by the thumbs of the folded wings.

The social behavior of the greater sac-winged bat can be observed easily from some distance. The mating system has been described as harem-polygynous, but recent studies using molecular genetic techniques proved that harem males father only 30% of the offspring within their harems. However, harem holders have on average a higher reproductive success than non-harem males and, therefore, males benefit from defending a group of females. The courtship of male S. bilineata includes visual, acoustic, and olfactory displays. Besides a large number of social calls that have been described for this species, males emit songs that can last for up to an hour and that include many different syllables. Songs of male S. bilineata are partly in the audible range of humans. In addition to singing, males also perform hovering flights during which fragrances are fanned towards roosting females. Males possess specialized holding sacs in the front wing membrane in which the fragrances are stored. The scents emanating from wing sacs of emballonunrid bats smell differently in different species. Histological studies proved that holding sacs of male S. bilineata and other emballonurid bats do not contain any glandular tissues. Male S. bilineata actively fill fragrances into the wing sacs each afternoon during a stereotyped behavioral sequence. During the first phase, which has been interpreted as cleaning, males swallow their urine and lick the holding sacs intensively. After approximately 10–20 minutes of cleaning, males rest for a few minutes and then switch to a second phase. During the second phase, males press their chin onto the penis and deposit a small droplet at their chin. Afterwards, males smear this droplet into one of the holding sacs with a sideward movement of the head. This secretion probably originates from the preputial glands. Additional droplets of the gular gland are also added to the holding sacs. When transferring genital and gular secretions to the holding sacs, males alternate between the two sacs, thus refilling almost equal amounts of fragrances into both wing sacs. The second phase of perfume-blending can last up to 20–30 minutes. It is unknown if other emballonurid species with wing sacs in the male sex show a similar behavior.

Feeding ecology and diet

Emballonurid bats are aerial insectivorous bats that can be easily observed hunting for insects in a slow butterflylike flight. Larger emballonurid species, like the genus Taphozous, have a more pronounced, powerful flight. Emballonurids are among the first bats to start foraging in the evening. During periods of bad weather, some species may even start foraging in the afternoon. Occasionally, some species also glean insects from leaves. The diet of neotropical emballonurids consists mostly of small insects, primarily beetles and flies. In S. bilineata, colony members forage in an area where only they have access to. When insect abundance is declining, the whole colony moves to a different foraging site. Within foraging areas, single individuals forage in beats of 32.8–98.4 ft (10–30 m). The proboscis bat, Rhynchonycteris naso, hunts insects above or close to water surfaces. Ghost bats, genus Diclidurus, forage above the canopy. The Old World members are similar in their diet to the New World members. The tomb bats, genus Taphozous, forage more in open spaces.

Reproductive biology

Bats of the family Emballonuridae usually give birth to a single offspring per year. Exceptions to this rule may be small species like the proboscis bat that reproduce twice each year. Most emballonurid bats show a seasonal pattern of reproduction with females giving birth to their offspring at the beginning of the rainy season. Sperm storage or delayed embryonic development occurs in some Old World members within the family Emballonuridae. The mating system varies by species.

Emballonurid bats exhibit a variety of different mating systems. Similar to other mammalian groups, polygynous mating patterns are most common. However, exceptions are for example the monogamous mating system of Cormura brevirostris and possibly also of the greater dog-faced bat, Peropteryx kappleri, and some members of the genus Taphozous. The proboscis bat is considered to have a promiscuous mating pattern. Among emballonurid bats, the greater sac-winged bat, Saccopteryx bilineata, is the best studied species.

Conservation status

The IUCN Chiroptera Specialist group lists two species as Critically Endangered (Coleura seychellensis, which is endemic to the Seychelles, and Taphozous troughtoni, of which only six specimen have ever been collected), two species as Endangered (Balantiopteryx infusca is threatened by habitat destruction and Emballonura semicaudata by development and cyclone damage), and 10 species as Vulnerable. In tropical regions, forest specialists seem to face an uncertain future if habitat destruction and forest fragmentation continues. Opportunistic species like Rhynchonycteris naso, Saccopteryx bilineata, or some species within the genus Taphozous may even live around buildings when humans do not distrub them.

Significance to humans

None known.

Species accounts

Resources

Eisenberg, J. F. Mammals of the Neotropics 1. The Northern Neotropics. Chicago and London: The University of Chicago Press, 1989.

Eisenberg, J. F., and K. H. Redford. Mammals of the Neotropics 3. The Central Neotropics. Chicago and London: The University of Chicago Press, 1999.

Emmons, L. H. Neotropical Rainforest Mammals—A Field Guide. Chicago and London: The University of Chicago Press, 1990.

Hutson, A. M., S. P. Mickleburgh, and P. A. Racey. Global Status Survey and Conservation Plan—Microchiropteran Bats. IUCN/SSC Chiroptera Specialist Group. Gland, Switzerland, and Cambridge, UK: IUCN Publications, 2001.

Kingdon, J. East African Mammals. Chicago and London: The University of Chicago Press, 1984.

Reid, F. A. A Field Guide to the Mammals of Central America and Southeast Mexico. New York and Oxford: Oxford University Press, 1997.

Nowak, R. M. Walker's Mammals of the World. 5th ed. Baltimore and London: The Johns Hopkins University Press, 1991.

Voigt C. C., G. Heckel, and O. von Helversen. "Conflicts and Strategies in the Mating System of the Sac-winged Bat." In Functional and Evolutionary Ecology of Bats, edited by G. F. McCracken, A. Zubaid, and T. H. Kunz. Oxford: Oxford University Press, 2003.

Bradbury, J. W., and L. Emmons. "Social Organization of some Trinidad bats. I. Emballonuridae." Zeitschrift für Tierpsychologie 36 (1974): 137.

Bradbury, J. W., and S. L. Vehrencamp. "Social Organization and Foraging in Emballonurid Bats. I. Field Studies." Behavioural Ecology and Sociobiology 1 (1976): 337. ——. "Social Organization and Foraging in Emballonurid Bats. III. Mating Systems." Behavioural Ecology and Sociobiology 2 (1977): 1.

Heckel, G., C. C. Voigt, F. Mayer, and O. von Helversen. "Extra-harem Paternity in the White-lined Bat Saccopteryx bilineata." Behaviour 136 (1999): 1173.

Voigt, C. C. "Individual Variation of Perfume-blending in Male Sac-winged Bats." Animal Behaviour 63 (2002): 907.

Voigt, C. C., and O. von Helversen. "Storage and Display of Odor by Male Saccopteryx bilineata (Chiroptera; Emballonuridae)." Behavioral Ecology and Sociobiology 47 (1999): 29.

[Article by: Christian C. Voigt, PhD]