Hypsignathus monstrosus is found in the forested regions of central Africa. It has been recorded from Senegal to northern Angola (Langevin and Barclay, 1990; Koopman, 1975).
Hammerhead bats are found at elevations less than 1800 m. They prefer riverine forests, swamps, mangroves, and palm forests. (MacNamara et al., 1979; Langevin and Barclay, 1990)
H. monstrosus is the largest bat found in Africa, with males being significantly larger than females. Males range in mass from 228 g to 450 g, averaging 377 g. Females are about half the size, weighing from 218 to 377 g, and averaging 275 g. Males range in length from 220 to 280 mm, with an average of 250 mm. Females measure 195 to 225 mm, averaging 210 mm. Males have a wingspan of 686 to 970 mm, and females have an average wingspan of 840 mm.
The species is sexually dimorphic in facial features as well as in size. Males have an enlarged rostrum and larynx, and a large, square head. They can also be distinguished by their huge, pendulous lips, flaps around a warty snout, a bald, split chin and cheek pouches. To human eyes, these bats are really ugly, prehaps accounting for their species name, "monstrosus." Females also have a square-shaped head, but their muzzle is fox-shaped and lacks the unique lip, snout, and chin characteristics of the male.
The ears are rounded at the base and the tail is very short. There is a claw on the second finger and this bat has large, flexible thumbs.
The pelage is slate-brown and there is a white collar of fur that stretches from shoulder to shoulder. The face and wing membranes are dark brown and the ears are dark brown with white tufts at the base.
(Langevin and Barclay, 1990; Kulzer, 1990; Macnamara et al., 1979)
H. monstrosus has a lek or arena mating system. The bats gather at night along a stream or river bed where males line up on tree branches in a long, narrow strip. They space themselves evenly in 10 m intervals and advertise themselves to females. An assemblage could contain from 25 to 132 bats.
Males attract females with loud vocalizations, including guttoral honking and croaking. They also use wing flapping. The bizzare head shape of the males of this species probably aids them in making favorable vocalization. Females fly through the arena to assess the males, then choose a mate and sit beside him on the branch.
Males emit a high buzz call when chosen and copulation begins. The duration of copulation is only 30-60 seconds and the pair leave independent of each other to forage. There are two mating sessions per night, one around 9:00 PM and the next at 4:00 AM. The early evening session is when most copulations occur and the later session is mainly for male agonistic behavior as they establish what territory in the strip will be theirs to display (Langevin and Barclay, 1990).
The species is highly polygynous. Nowak (1999) reports that only 6 percent of the males in a population accounted for 79 percent of matings. The successful males tended to be clumped together in the assemlage of males, indicating the importance of territory within the strip.
Data on when hammerhead bats breed vary. Some studies suggest that the peak of births occurs August to September during the middle of the rainy season and then another at the end of the rainy season, from October to December (Wolton et al., 1982). Others suggest the breeding peaks are at six month intervals and that are synchronized with the two dry seasons (Bradbury, 1977). In captivity, females maintain the same cycle they exhibit in the wild, breeding during June to August, and again in December to January (Nowak, 1999).
Females typically produce one offspring at a time, although twins have been seen. Newborn hammerhead bats weigh about 40 g (Nowak, 1999). Gestation length has not been reported for this species, nor has time until weaning. other Pteropodids vary greatly in these parameters, so it is difficult to speculate on this species based trends within the family.
The male H. monstrosus reaches sexual maturity at approximately 18 months and does not develop sexually dimorphic facial features until 12 months. Females are sexually mature at 6 months and full size at 12 months (Bradbury, 1977).
Parental care has not been reported for this species, but is likely to be the responsibility solely of females. Females provide milk, protection, grooming, and other essentials to the young in highly polygynous species. In some species, females carry their young with them while they fly around, and in others females park their young in roosts while they forage. There are no reports regarding what H. monstrosus does with its young.
The hammerhead bat has a life expectancy of up to 30 years (Kulzer, 1990).
This species is nocturnal. The most studied behavior of hammerhead bats is the lek mating system (see Reproduction, above). H. monstrosus is social, roosting during the day in groups of up to 25, but with an average roosting group size of 4-5 individuals. Each individual spaces itself 10-15 cm from others, the only exception being a mother and her offspring. These bats roost in mixed age and sex assemblages, and they may change roosts daily (Langevin and Barclay ,1990).
MacNamara et al. (1979) suggest that individuals space themselves out during situations of stress.
As noted in other sections of this account, males and females have different foraging strategies, with males ranging farther for higher quality food than females.
Figs make up most of the H. monstrosus diet, but this bat may also include the juice and soft pulp of mangos, bananas and guavas. Van Deusan (1968) reports H. monstrosus showing some carnivorous behavior by attacking chickens to drink their blood and scavenging for meat.
Males and females use different foraging strategies. The females rely on established, dependable food resources of moderate quality. The males prefer to search out high quality food patches, flying up to 10 km to find the best food (Bradbury ,1981). This difference may reflect different metabolic needs, based on the difference in size between males and females.
To avoid predation, the hammerhead bat roosts high in forest canopy (20-30m), in groups of up to 25 individuals. During the day, they are inactive and rely on camouflage to hide them from predators (Kulzer, 1990).
Although humans and birds of prey may take some of these bats, parasites seem to be the main threat to their health. These have their own specific hepatoparasite, Hepatocystis carpenteri (Langevin and Barclay, 1990).
Although hammerhead bats are frugivorous, they consume mainly the juice and occasionally the pulp of their meal. Because of this, they are not very good seed distributors. However, given their size, they make a pretty good meal for a bird of prey and may affect prey populations, dependingupon their availability (Langevin and Barclay, 1900).
There have been no reports of the affect of this bat on humans. However, humans do hunt these animals, as noted under Predation, above, so they do provide food.
This species has been reported to kill chickens (see Food Habits, above).
This species has no special conservation status.
Julia Boland (author), Humboldt State University, Brian Arbogast (editor), Humboldt State University.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
flesh of dead animals.
uses smells or other chemicals to communicate
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
an animal that mainly eats fruit
An animal that eats mainly plants or parts of plants.
fertilization takes place within the female's body
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
generally wanders from place to place, usually within a well-defined range.
having more than one female as a mate at one time
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
Bradbury, J. 1977. Lek mating behavior in the hammer-headed bat. Zeit. fur Tierpsychol, 45: 225-255.
Kulzer, E. 1990. Bats. Grzimek's Encyclopedia of Mammals: 536-631.
Langevin, P., R. Barclay. 1990. Hypsignathus monstrosus. Mammalian Species, 357: 1-4.
MacNamara, M., S. Doherty, A. Schacter. 1980. The management and breeding of hammerhead bats at the New York Zoological Park. International Zoo Yearbook, 20: 260-264.
Nowak, R. 1999. Walker's mammals of the world, Sixth edition. Baltimore and London: The Johns Hopkins University Press.
Van Deusen, H. 1968. Carnivorous habits of *Hypsignathus monstrosus*. Journal of Mammalogy, 49: 335-336.
Wolton, R., P. Arak, H. Godfray, R. Wilson. 1982. Ecological and behavioural studies of the Megachiroptera at Mount Nimba, Liberia, with notes on Microchiroptera. Mammalia, 46: 419-448.