Bulldog bats

(Noctilionidae)

Class Mammalia

Order Chiroptera

Suborder Microchiroptera

Family Noctilionidae

Thumbnail description
Noctilionids get their common name from their distinctive full and pendant lips and cheek pouches, which makes them look much like a bulldog; their legs are long and their feet and claws are large; give off a pungent, fishy odor

Size
Large bats ranging 2.1–3.6 in (54–92 mm) in forearm length and weighing 0.6–7.8 oz (18–78 g)

Number of genera, species
1 genus; 2 species

Habitat
Tropical lowland areas near water

Conservation status
Overall not threatened, though regional populations may be at risk

Distribution
Neotropical

Evolution and systematics

The systematic affinities of the family Noctilionidae were debated for many years. Recent analyses of large molecular and morphological datasets provide strong evidence that these bats are closely allied with the other exclusively neotropical bat families, Mormoopidae and Phyllostomidae, and with the endemic New Zealand family, Mystacinidae, that together form the superfamily Noctilionoidea.

Analyses of molecular variation among populations of the two noctilionid species and their close relatives, the mormoopids, suggest that the evolution of a fish-eating lifestyle in Noctilio leporinus is relatively recent, within three million years. These data also suggest the possibility that Noctilio albiventris is actually composed of two, distinct lineages that diverged from each other approximately one to three million years ago. Additional data are needed to evaluate fully this possibility.

Fossils of an extinct species of Noctilio are now known from the late Miocene in the Amazon Basin.

Physical characteristics

The muzzle and elongate feet and legs of bulldog bats are their most distinctive features. The nose and muzzle are simple, but a projecting nose-pad, enlarged and swollen lips, pronounced cheek pouches, and folds of skin on the lower lip give these bats a bulldog-like appearance. The ears are separate, long, and narrow, with a lobed tragus. The tail emerges dor-sally from the tail membrane about one-third of its length from the body. The calcar, or heel extension, of these bats is long and bony. Both species have long legs with well-developed feet and claws, but the modification of the claws and feet into large, razor-sharp, and hydrodynamically efficient gaffing mechanisms in Noctilio leporinus is truly astounding.

Bulldog bats are fairly large, with short pelage ranging in color from bright orange to orange-brown and gray-brown. Fur color was previously thought to represent differences between sexes, with males being orange and females brown. It is now understood that color is quite variable within each species. A white line, which may or may not be distinct, runs

down the center of the back from the shoulder region to the rump. Wing and tail membranes are brown.

Total body lengths range 2.2–5.1 in (57–132 mm), forearm lengths 2.1–3.6 in (54–92 mm), and weights range 0.6–7.8 oz (18–78 g). Males are significantly larger than females in both species.

Both species have well-developed teeth typical of most insectivorous bats. The dental formula is: I2/1 C1/1 P1/2 M3/3.

Distribution

Bulldog bats are found throughout much of the Neotropics, from southern Mexico to northern Argentina and southeastern Brazil, and in the Antilles.

Habitat

Bulldog bats are found in a variety of habitats, most commonly in moist, tropical lowland areas that are close to water. They have been recorded roosting in hollow trees and sea caves.

Behavior

Information on behavior is limited to general observations on roosting and activity patterns. Few studies of social or mating behaviors have been conducted. The two species differ in activity patterns throughout the night, but are similar in their choice of roosts (hollow trees, caves, and human-made structures), reproductive biology, and general foraging behavior, though N. leporinus preys mainly on fish, and N. albiventris primarily on insects.

Feeding ecology and diet

Noctilio leporinus is best known for its remarkable set of adaptations to piscivory. Only one other bat species worldwide is known to prey on fish: Myotis vivesi (Vespertilionidae). N. albiventris is primarily insectivorous, and N. leporinus also includes a large proportion of insects in the diet. Both species use their large cheek pouches to store partially chewed food, possibly allowing them to continue foraging without having to stop to consume their prey fully, as in most bats.

Bulldog bats use constant frequency and frequencymodulated echolocation to detect prey at the surface of the water and in flight. The rear feet are dragged through the water and used to gaff prey at the surface. The stiff, elongate calcars are used to elevate the tail membrane above the surface of the water, minimizing drag. Prey are sometimes transferred to the tail membrane and then to the mouth during flight.

Reproductive biology

Field studies suggest that females of both species give birth to a single young each year, with the majority of mating in November and December and births occurring in April through June. However, pregnancy and births have been recorded outside of these seasons in different parts of their ranges and a secondary reproductive peak has been recorded for Noctilio leporinus in Cuba. Young are able to fly at about one month of age. Males and females seem to attend the young during their first month of life, suggesting extensive biparental care. A single male typically lives with a harem of females in a polygynous organization. Mating behaviors are unknown, but a warty out-pocket of skin on the scrotum in males, and scent-producing glands associated with it, may be involved.

Conservation status

Populations seem to be stable, although bulldog bats will be negatively affected by water contamination and habitat destruction. Noctilio leporinus has been proposed as an indicator species for water quality because of the likelihood that contaminants will accumulate in their tissues through predation on aquatic insects and fish.

Significance to humans

Bulldog bats eat insects that may be considered pests by humans.

Species accounts

List of Species

Greater bulldog bat

Noctilio leporinus

taxonomy

Noctilio leporinus (Linnaeus, 1758), Suriname. Three subspecies are recognized.

other common names

English: Fishing bat, bulldog bat.

physical characteristics

Head and body length 4.6–5 in (119–127 mm); forearm length longer than 2.9 in (75 mm); hindfoot length >0.9 in (>25 mm); combined foot and tibia length: >1.9 in (>50 mm); wingspan 19.6 in (500 mm); tail length 0.9–1.1 in (25–28 mm); ear length 1.10–1.16 in (28–29.5 mm); weighing more than 1.7 oz (50 g). Vary in size geographically, with larger individuals in the northern and southern parts of the range, and smaller individuals in the Amazon Basin. Males are larger than females; they can be distinguished from their smaller congeners, lesser bulldog bats, by their larger size and more highly modified feet.

distribution

Found from Sinaloa and Veracruz in Mexico south to northern Argentina. They are also found throughout many of the Antillean islands.

habitat

Restricted to moist, lowland, and coastal areas within their range, including major river basins, coastal embayments, and lakes.

behavior

Colonies of up to several hundred individuals have been found roosting in hollow trees and sea caves. They have been found roosting in association with several other species of bats. They are active throughout the night; groups of five to 15 animals emerge to forage together. Time of roost emergence may be influenced by temperature.

feeding ecology and diet

Famous for their fish-eating habits. Aquatic and flying insects also comprise a large portion of the diet and they have been known to eat shrimp and crabs. They have several notable adaptations to their piscivorous lifestyle, including their greatly enlarged feet and claws, elongated calcar, robust and sharp teeth, and specializations of the stomach that allow them to ingest very large prey, including fish up to 4.7 in (120 mm) long. The bats fly low over water bodies while foraging and emit echolocation pulses, which allow them to detect tiny surface disturbances. They then use their long, sharp claws to drag through the water and gaff their prey.

reproductive biology

Information on reproduction is mainly available from Central American and Antillean sites and breeding season may vary regionally. Mating seems to coincide with wet seasons, when insects and fish are most abundant; it typically begins in November and December, with births occurring from April through June. A second mating season has been suggested in parts of the range, with mating occurring in the summer and births from October–December. Males and females may contribute to caring for offspring. Young begin to emerge from roosts and fly at about one month of age. A captive lived to 11 years and six months old. This species is probably polygynous.

conservation status

Currently abundant throughout their range.

significance to humans

Control insect populations and may act as indicator species of water contaminant levels.

Lesser bulldog bat

Noctilio albiventris

taxonomy

Noctilio albiventris Desmarest, 1818, Bahia, Brazil. Formerly known as Noctilio labialis, four subspecies are recognized.

other common names

None known.

physical characteristics

Head and body length 2.5–2.6 in (65–68 mm); forearm length 2.7 in (70 mm); foot length <0.7 in (<20 mm); combined foot and tibia length <1.5 in (<40 mm); tail length 0.5–0.6 in (13–16 mm); ear length 0.8–0.9 in (22–24 mm); wingspan 11.2–14.9 in (285–380 mm). Males are significantly larger than females in body measurements and in the development of the sagittal crest. Distinguished from greater bulldog bats by their smaller size and less extravagantly modified feet.

distribution

Occurs from Honduras and western Guatemala in the north to Argentina, Paraguay, and coastal Brazil in the south.

habitat

Forage over rivers, streams, and wetlands in wet, tropical forests up to an altitude of 3,610 ft (1,100 m).

behavior

Available evidence suggests that there are two activity peaks in a night, one soon after dusk and another after midnight. Foraging occurs in small groups over bodies of water. Roosts are occupied by small to large groups of bats; they can be found roosting with Molossus species.

feeding ecology and diet

Primarily insectivorous. Analyses of stomach contents and feces suggest that they eat a wide variety of insects, some of which are taken from the water. In some areas, individuals have been found with fish scales, pollen, and fruit seeds in their stomachs as well. They forage in groups of eight to 15.

reproductive biology

Most likely polygynous. Females give birth to one young per year. Breeding season may vary regionally, but available evidence suggests that breeding occurs once yearly. Pregnant females have been recorded primarily from February through May. A captive infant was nursed for nearly three months.

conservation status

Currently abundant throughout their range.

significance to humans

Control populations of potential insect pests.

Resources

Books

Hill, John E., and James D. Smith. Bats, A Natural History. London: British Museum of Natural History, 1984.

Koopman, Karl F. "Chiroptera: Systematics." In Handbook of Zoology, Volume VIII, Mammalia, edited by J. Niethammer, H. Schliemann, and D. Starck. Berlin: Walter de Gruyter, 1994.

McKenna, Malcolm C., and Susan K. Bell, eds. Classification of Mammals Above the Species Level. New York: Columbia University Press, 1997.

Nowak, Ronald M. Walker's Bats of the World. Baltimore: Johns Hopkins University Press, 1994.

Simmons, Nancy B., and Jonathan H. Geisler. "Phylogenetic Relationships of Icaronycteris, Archaeonycteris, Hassianycteris, and Palaeochiropteryx to Extant Bat Lineages, with Comments on the Evolution of Echolocation and Foraging Strategies in Microchiroptera." Bulletin of the American Museum of Natural History, Number 235. New York: American Museum of Natural History, 1998.

Periodicals

Altenbach, J. Scott. "Prey Capture by the Fishing Bats Noctilio leporinus and Myotis vivesi." Journal of Mammalogy 70 (1989): 421–424.

Brooke, Anne P. "Diet of the Fishing Bat, Noctilio leporinus (Chiroptera: Noctilionidae)." Journal of Mammalogy 75 (1994): 212–218.

Czaplewski, Nicholas J. "Opossums (Didelphidae) and Bats (Noctilionidae and Molossidae) from the Late Miocene of the Amazon Basin." Journal of Mammalogy 77 (1996): 84–94.

Fenton, M. B., et al. "Activity Patterns and Roost Selection by Noctilio albiventris (Chiroptera: Noctilionidae) in Costa Rica." Journal of Mammalogy 74 (1993): 607–613.

Fish, Frank E., Brad R. Blood, and Brian D. Clark. "Hydrodynamics of the Feet of Fish-catching Bats: Influence of the Water Surface on Drag and Morphological Design." The Journal of Experimental Zoology 258 (1991): 164–173.

Hood, Craig, S., and Jay Pitocchelli. "Noctilio albiventris." Mammalian Species 197 (1983): 1–5.

Hood, Craig S., and J. Knox Jones, Jr. "Noctilio leporinus." Mammalian Species 216 (1984): 1–7.

Lewis-Oritt, Nicole, Ronald A. Van Den Bussche, and Robert J. Baker. "Molecular Evidence for Evolution of Piscivory in Noctilio (Chiroptera: Noctilionidae)." Journal of Mammalogy 82 (2001): 748–759.

Mendez, L., and S. T. Alvarez-Castañeda. "Comparative Analysis of Heavy Metals in Two Species of Ichthyophagous Bats Myotis vivesi and Noctilio leporinus." Environmental Contamination and Toxicology 65 (2000): 51–54.

Roverud, Roald C., and Mark A. Chappell. "Energetic and Thermoregulatory Aspects of Clustering Behavior in the Neotropical Bat Noctilio albiventris." Physiological Zoology 64 (1991): 1527–1541.

Van Den Bussche, Ronald A., and Steven R. Hoofer. "Further Evidence for Inclusion of the New Zealand Short-tailed Bat (Mystacina tuberculata) within Noctilionoidea." Journal of Mammalogy 81 (2000): 865–874.

Van Den Bussche, Ronald A., Steven R. Hoofer, and Nancy B. Simmons. "Phylogenetic Relationships of Mormoopid Bats Using Mitochondrial Gene Sequences and Morphology." Journal of Mammalogy 83 (2002): 40–48.

Tanya Dewey