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).
Biogeographic Regions: ethiopian (Native )
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)
Range mass: 218-228 to 377-450 g.
Average mass: 275-377 g.
Range length: 195-220 to 225-280 mm.
Average length: 210-250 mm.
Range wingspan: 686 (males) to 970 (males) mm.
Average wingspan: 840 (females) mm.
Sexual Dimorphism: male larger
Other Physical Features: endothermic ; bilateral symmetry
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)
Range elevation: 1800 (high) m.
Habitat Regions: tropical
Terrestrial Biomes: forest
Other Habitat Features: riparian
Habitat and Ecology
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.
Animal Foods: blood; carrion
Plant Foods: fruit
Primary Diet: herbivore (Frugivore )
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).
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).
- humans (Homo sapiens)
- birds of prey (Falconiformes and Strigiformes)
This list may not be complete but is based on published studies.
Life History and Behavior
Perception Channels: tactile ; chemical
The hammerhead bat has a life expectancy of up to 30 years (Kulzer, 1990).
Status: wild: 30 years.
Lifespan, longevity, and ageing
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.
Mating System: polygynous
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).
Breeding season: Breeding probably occurs in late summer and early in winter.
Range number of offspring: 1 to 2.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous
Average birth mass: 40 g.
Average number of offspring: 1.3.
Average age at sexual or reproductive maturity (male)
Sex: male: 420 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 180 days.
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.
Parental Investment: female parental care
This species has no special conservation status.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: least concern
IUCN Red List Assessment
Red List Category
Red List Criteria
- 2004Least Concern
- 1996Lower Risk/least concern(Baillie and Groombridge 1996)
Relevance to Humans and Ecosystems
This species has been reported to kill chickens (see Food Habits, above).
Negative Impacts: crop pest
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.
Positive Impacts: food
The hammer-headed bat (Hypsignathus monstrosus), also known as the big-lipped bat, is a megabat widely distributed in equatorial Africa. This large bat is found in riverine forests, mangroves, swamps, and palm forests at elevations less than 1,800 metres (5,900 ft).
The hammer-headed bat is a member of the family Pteropodidae. Pteropodidae is divided into two subfamilies, Macroglossinae which contains six genera, and Pteropodinae containing thirty-six genera including Hypsignathus. The family Pteropodidae is found within the suborder, Megachiroptera. This group is commonly referred to as the megabats or flying foxes.
The hammer-headed bat is the largest bat in Africa with a wingspan of 686 to 970 mm (27.0 to 38.2 in) and a total length of 195 to 285 mm (7.7 to 11.2 in). Males, ranging from 228 to 450 g (8.0 to 15.9 oz), are significantly larger than females, which range from 218 to 377 g (7.7 to 13.3 oz).
Pelage is grey-brown to slaty-brown with a whitish collar of fur extending from shoulder to shoulder. The flight membranes are brown and the ears are dark brown with a tuft of white fur at the base. The face is dark brown with a few long, stiff whiskers around the mouth.
The skull may be diagnosed by specific dental features. The second premolar and molars are markedly lobed. This feature is specific for this genus, and no other African fruit bats have this characteristic.
There is extreme sexual dimorphism in this species. The male possesses an enormous head for producing loud honking calls. The enlarged rostrum, larynx and lips allow these sounds to be extremely resonant. The larynx is one half the length of the vertebral column and fills out most of the thoracic cavity. It is nearly three times larger in males than females. The male also has a hairless split chin and warty rostrum with wrinkled skin around it. Females have a much more fox-like appearance similar to most fruit bats.
Ecology and behavior
Hammer-headed bats are frugivores. Figs make up much of their diet, but they may also include mangos, bananas and guavas. There are some complications inherent in a fruit diet such as insufficient protein intake. It is suggested that fruit bats compensate for this by possessing a proportionally longer intestine compared to insectivorous species. This enhances their ability to absorb protein. They also have very rapid digestive systems allowing these bats to assimilate high amounts of fruit to ensure that adequate protein is absorbed. It is also suggested that by eating a wide variety of fruits with varying protein contents, fruit bats are able to maintain an entirely frugivorous diet.
Generally fruit is picked and taken to a nearby tree where it is chewed, the juice squeezed out and the pulp discarded. Since they often do not consume the pulp, these bats are not considered to be good seed distributors. Males may forage long distances (up to 10 km or 6 mi) to locate the highest quality food. Females rely on established feeding routes that offer a constant supply of lower quality food. This may reflect different metabolic requirements based on body size differences.
Large bats often experience difficulties with overheating during flight. The limited thermoregulatory capabilities of flying bats appears to be one factor closely associated with why flight activity primarily occurs during cooler nocturnal temperatures. It has been found that hammer-headed bats are able to tolerate higher ambient temperatures during flight than other bats. This ability is associated with this bat’s high thermal conductance (Cf) which is defined as the total heat loss less the heat loss due to evaporation divided by body temperature less the ambient temperature (Cf = [H1 – He]/[Tb – Ta]). However, they are especially sensitive to ambient temperatures below 11 °C (52 °F) and a decrease in flight coordination is seen. Due to the large surface area of the wing, convective heat loss to cool air may be significant enough to chill flight muscles preventing the precise coordination essential for flight.
These bats are nocturnal, roosting during the day in the forest canopy. They rely on camouflage to hide them from predators. Specific species of trees are not selected for roosting, however some roosts may be used for long periods of time. Roosts are generally 20–30 metres (70–100 ft) from the ground.
The main predators of this species are humans and nocturnal and diurnal birds of prey. However, infection by parasites is often the most significant problem for the hammer-headed bat. Adults are often infected with mites and the hepatoparasite, Hepatocystis carpenteri.
Reproduction and mortality
Little is known about reproduction in hammer-headed bats. In some populations breeding is thought to take place semi-annually during the dry seasons. The timing of the dry season varies depending on the locality, but in general there are two breeding seasons, one from June to August and the other from December to February. However, in other populations, breeding is not restricted to dry seasons and occurs during all months of the year.
This species is often cited as a classic model of lek mating. In this type of mating system, males cluster in dense groups at specific locations known as mating arenas. In some populations of hammer-headed bats, males gather along rivers at night and display by rapid wing flapping accompanied by loud vocalizations. An arena may contain from 25 to 132 males. Females fly through the arena assessing the males. Once the female’s choice is made, the female lands on the branch and sits beside the male. Once chosen, the male emits a buzzing call and copulation ensues.
However, some populations of hammer-headed bats do not use the lek mating strategy. Males actively display but are not found clustering in groups. This species is highly polygamous. Some estimates suggest that as few as six percent of the males in a population account for up to seventy-nine percent of the matings.
Females generally produce one offspring at a time. Neither gestation nor time until weaning have been reported for this species. Females mature more quickly than males and are sexually mature after six months. They continue to grow and reach adult size at nine months. Males do not reach sexual maturity until approximately eighteen months of age and they do not obtain their unique facial morphology until twelve months. Compared with other bats, this bat is rather long-lived with an average life expectancy of thirty years in the wild.
Interactions with humans
H. monstrosus has no special conservation status. In 2004, the IUCN Red List of Threatened Species listed this species as LC (least concern) on the basis of its widespread distribution and lack of threats to its habitat.
Due to this bat’s diet of fruit, it may be considered a crop pest. It has also been observed to attack live chickens. This observation was reported once and cannot be considered a regular occurrence. Humans hunt this large bat and consume it as bushmeat.
The hammer-headed bat is one of three species of African fruit bat claimed to be asymptomatically infected with the Ebola virus. It is not known whether these species are incidental hosts or a reservoir of Ebolavirus infection for humans and other terrestrial mammals.
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