Perception Channels: tactile ; chemical
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
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
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).
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 )
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 )
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
Wetlands: swamp
Other Habitat Features: riparian
The hammerhead bat has a life expectancy of up to 30 years (Kulzer, 1990).
Average lifespan
Status: wild: 30 years.
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
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).
Known Predators:
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
The hammer-headed bat (Hypsignathus monstrosus), also known as hammer-headed fruit bat, Hammerhead Bat, and big-lipped bat, is a megabat widely distributed in West and Central Africa. It is the only member of the genus Hypsignathus, which is part of the tribe Epomophorini along with four other genera. It is the largest bat in continental Africa, with wingspans approaching 1 m (3.3 ft), and males almost twice as heavy as females. Males and females also greatly differ in appearance, making it the most sexually dimorphic bat species in the world. These differences include several adaptations that help males produce and amplify vocalizations: the males' larynges (vocal cords) are about three times as large as those of females, and they have large resonating chambers on their faces. Females appear more like a typical megabat, with foxlike faces.
The hammer-headed bat is frugivorous, consuming a variety of fruits such as figs, bananas, and mangoes, though a few instances of carnivory have been noted. Females tend to travel a consistent route to find predictable fruits, whereas males travel more to find the highest quality fruit. It forages at night, sleeping during the day in tree roosts. Individuals may roost alone or in small groups. Unlike many other bat species that segregate based on sex, males and females will roost together during the day. It has two mating seasons each year during the dry seasons. It is believed to be the only bat species with a classical lek mating system, wherein males gather on a "lek", which in this case is a long and thin stretch of land, such as along a river. There, they produce loud, honking vocalizations to attract females. Females visit the lek and select a male to mate with; the most successful 6% of males are involved in 79% of matings. Offspring are born five or six months later, typically a singleton, though twins have been documented. Its predators are not well-known, but may include hawks. Adults are commonly affected by parasites such as flies and mites.
The hammer-headed bat is sometimes considered a pest due to its frugivorous diet and its extremely loud honking noises at night. In Nigeria and the Democratic Republic of the Congo, it is consumed as bushmeat. It has been investigated as a potential reservoir of the Ebola virus, with several testing positive for antibodies against the virus. It is not considered a species of conservation concern due to its large range and presumably large population size.
Hypsignathus
Position of Hypsignathus within Pteropodidae[2]The hammer-headed bat was described as a new species in 1861 by American scientist Harrison Allen. Allen placed the species into a newly-created genus, Hypsignathus.[3] The holotype had been collected by French-American zoologist Paul Du Chaillu[3] in Gabon.[4] The genus name Hypsignathus comes from the Ancient Greek húpsos, meaning "high", and gnáthos, meaning "jaw". T. S. Palmer speculated that Allen chose the name Hypsignathus to allude to the "deeply arched mouth" of the species.[5] The species name monstrosus is Latin for "having the qualities of a monster".[6]
A 2011 study found that Hypsignathus was the most basal member of the tribe Epomophorini, which also includes Epomops, Micropteropus, Epomophorus, and Nanonycteris.[2] Initially, Allen identified the hammer-headed bat as a member of the subfamily Pteropodinae of the megabats.[3] However, in 1997, Epomophorini was recognized as part of the subfamily Epomophorinae.[7] Some taxonomists do not recognize Epomophorinae as a valid subfamily and include its taxa, including the Epomophorini, within Rousettinae.[8][9]
The hammer-headed bat is the largest bat in mainland Africa.[10] Males have wingspans up to 90.1 cm (2.96 ft),[11] and all individuals have forearm lengths exceeding 112 mm (4.4 in).[10] It has pronounced sexual dimorphism, more so than any other bat species in the world,[10] with males up to twice as heavy as females. The average weight of males is 420 g (15 oz), compared to 234 g (8.3 oz) for females.[11] Other differences between the sexes relate to their social system, in which males produce loud, honking vocalizations. Therefore, males have greatly enlarged larynges, about three times the size of females',[12] extending through most of the thoracic cavity, and measuring half the length of the spine. The larynx is so large, it displaces other organs, including the heart, lungs, and gastrointestinal tract.[12] Males also have resonating chambers to increase the volume of sound production. These chambers are pharyngeal air sacs connected to a large sinus in the humped snout.[10] These numerous adaptations caused scientists Herbert Lang and James Chapin to remark, "In no other mammal is everything so entirely subordinated to the organs of voice".[13]
Males overall have boxy heads with enormous lips, while the females, with their narrower snouts, have more foxlike faces.[12] Males and females both have dark brown fur, with a paler mantle (sides and back of neck). It has patches of white fur at the base of the ears, though sometimes indistinct. The fur is long and smooth, though somewhat woolly in texture on the mantle. The ears are triangular and blackish-brown, and the eyes are very large.[10] The dental formula is 2.1.2.12.1.3.2 for a total of 28 teeth; very occasionally, individuals have been found with an additional upper premolar on each side of the mouth, for a total of 30 teeth. The skull is larger and more robust than any other megabat in Africa, with a pronounced, massive snout. The tongue is large and powerful, with an expanded, tridentate tip. The tongue has backwards-facing papillae used to extract juice from fruits.[10]
The wings are characterized by low aspect ratio, meaning that it has a smaller wingspan relative to the wing area. The wing loading is considered exceptionally high, meaning that it has a large body weight relative to the wing area. The wings are blackish brown in color.[10] The thumb is approximately 128–137 mm (5.0–5.4 in) long.[12] The wings attach to the hindlimbs at the second toe. It lacks a tail.[10]
Instead of the typical mammalian karyotype where females have two X chromosomes and males have one each of X and Y, males have a single X chromosome and no Y chromosome, known as X0 sex-determination system.[10] Thus, females have 36 chromosomes (34 autosomes and two sex chromosomes), and males have 35 chromosomes (34 autosomes but only one sex chromosome).[14] This is seen in a few other bat genera, including Epomophorus and Epomops.[15][16]
Hammer-headed bats are frugivores. Figs make up much of their diet, but mangos, bananas and guavas may also be consumed. 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.[12]
Males and females rely on different strategies for foraging. Females use trap-lining, in which they travel an established route with dependable and predictable food sources, even if the food is lower quality. Males, in contrast, search for areas rich with food, traveling up to 10 km (6.2 mi) to reach particularly good food patches.[12] Upon finding suitable fruit, the hammer-headed bat may eat at the tree or pick the fruit and carry it away to another site for consumption. It chews the fruit, swallowing the juice and soft pulp, before spitting out the rest.[12] The guano (feces) typically contains seeds from ingested fruits, indicating that it may be an important seed disperser.[10]
Van Deusan (1968) reports H. monstrosus showing some carnivorous behavior by attacking chickens to drink their blood and scavenging for meat.[17]
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 the first breeding season is from June to August and the second is from December to February. Females may become pregnant up to twice per year, giving birth after five or six months gestation[10] to one offspring at a time,[12] though twins have been reported.[13] Newborns weigh approximately 40 g (1.4 oz) at birth.[13] Females reach sexual maturity faster than males, and can reproduce at six months. Females reach adult size by nine months of age. In contrast, males are not sexually mature until eighteen months. Males and females are similar in size for their first year of life.[12]
This species is often cited as an example of classical lek mating,[18] and is perhaps the only bat species with such.[19] The classical lek is defined by four criteria:[10]
Males form these leks along streams or riverbeds during the mating season, which lasts 1–3 months.[12] Leks consist of 20–135 males in an area about 40 m (130 ft) wide and 400–1,600 m (1,300–5,200 ft) long.[10] Each male claims a display territory of about 10 m (33 ft) in diameter,[11] in which he honks repeatedly and flaps his wings while hanging from a branch.[12] Typically, 60–120 honks are produced per minute.[18] Males display for around four hours before foraging, with peaks in lekking activity in the early evening and before dawn. The early evening peak is when the majority of copulation occurs. Females will fly through the lek, selecting a male by landing on a branch next to him. The chosen male emits a "staccato buzz" call, followed immediately by copulation, which lasts 30–60 seconds.[12] After copulation, the female immediately departs, and the male resumes displaying.[10] The males at the center of the lek have the most success, and are responsible for the majority of matings:[12] the top 6% of males have 79% of the total matings.[10] In the before-dawn peak in activity, copulation is less frequent, and males spend time jockeying with each other for the best display territory. As the mating season progresses, the importance of the before-dawn peak lessens.[12]
However, some populations of hammer-headed bats in West Africa do not use leks. Instead, they have a harem system.[20]
During the day, the hammer-headed bat roosts in trees, typically 20–30 m (66–98 ft) above the ground in the forest canopy. Various trees are used for roosting, with no preference for a particular species. It has low fidelity to its roost and will move to a new roost after 5–9 days.[10] It relies on camouflage to hide from predators.[12] It displays a mix of solitary and social behavior. Individuals of both sexes are frequently found roosting alone, though they may roost in small groups of around four individuals. Occasionally, groups of up to twenty-five have been documented. Groups are of mixed sex and age, unlike other bat species which segregate based on sex. While roosting, individuals in a group are approximately 10–15 cm (3.9–5.9 in) apart, with males on the periphery and females nearer the center.[10] During most of the day, individuals sleep with their noses covered by their wings.[18] Members of the same group show little interaction with each other: they do not "squabble", vocalize, or groom each other. Instead, at sunset, individuals groom themselves then set off independently to forage.[10]
Its predators are not well-documented, but may include avian species such as the long-tailed hawk.[21] It has a diverse array of parasites, including such ectoparasites as the bat fly (Nycteribiidae) Dipseliopoda arcuata, the spinturnicid mite Ancystropus aethiopicus, the gastronyssid mite Mycteronyssus polli, and the teinocoptid mite Teinocopties auricularis.[10] Internally, it is known to be affected by the liver parasite Hepatocystis carpenteri. Adults commonly host parasites.[12]
The hammer-headed bat is a lowland species, always occurring below 1,800 m (5,900 ft) above sea level.[12] Most records of this species occur in rainforest habitat, including lowland rainforest, swamp forest, riverine forests, and mosaics of forest and grassland. While it has been documented in savanna habitats, these records are rare, and it has been speculated that these individuals are vagrants.[10] It has a wide range in West and Central Africa, including the following countries: Angola, Benin, Burkina Faso, Cameroon, Central African Republic, Republic of the Congo, Democratic Republic of the Congo, Ivory Coast, Equatorial Guinea, Ethiopia, Gabon, Ghana, Guinea, Guinea-Bissau, Kenya, Liberia, Nigeria, Sierra Leone, Sudan, Togo, and Uganda.[1]
As a frugivorous species, the hammer-headed bat is sometimes considered a pest of fruit crops.[22] Its ability to produce extremely loud vocalizations means that some consider it one of Africa's most significant nocturnal pests.[10] Humans hunt this large bat and consume it as bushmeat.[22] It is eaten in Nigeria,[23] as well as seasonally in the Democratic Republic of the Congo.[24]
The hammer-headed bat has been investigated as a potential reservoir of the Ebola virus. Some individuals have tested seropositive for the virus, meaning that they had antibodies against the virus, though the virus itself was not detected. Additionally, nucleic acid sequences associated with the virus have been isolated from its tissues.[25] However, the natural reservoirs of ebolaviruses are still unknown as of 2019.[26][27][28] Megabats like the hammer-headed bat tend to be over-sampled relative to other potential Ebola virus hosts, meaning that they may have an unwarranted amount of research attention, and as of 2015, no bat hunter or researcher is known to be the index case ("patient zero") in an Ebola outbreak.[29]
As of 2016, the hammer-headed bat is evaluated as a least-concern species by the IUCN—its lowest conservation priority. It meets the criteria for this classification because it has a wide geographic range; its population is presumably large; and it is not thought to be experiencing rapid population decline.[1] It is not a common bat species in captivity, though it is kept at the Wrocław Zoo in Poland as of 2020,[30] and was kept at the Bronx Zoo and San Diego Zoo Safari Park in the 1970s and 1980s. In captivity, hammer-headed bats, particularly males, are vulnerable to stress-related illness, especially when moved or placed in new enclosures.[31]
The hammer-headed bat (Hypsignathus monstrosus), also known as hammer-headed fruit bat, Hammerhead Bat, and big-lipped bat, is a megabat widely distributed in West and Central Africa. It is the only member of the genus Hypsignathus, which is part of the tribe Epomophorini along with four other genera. It is the largest bat in continental Africa, with wingspans approaching 1 m (3.3 ft), and males almost twice as heavy as females. Males and females also greatly differ in appearance, making it the most sexually dimorphic bat species in the world. These differences include several adaptations that help males produce and amplify vocalizations: the males' larynges (vocal cords) are about three times as large as those of females, and they have large resonating chambers on their faces. Females appear more like a typical megabat, with foxlike faces.
The hammer-headed bat is frugivorous, consuming a variety of fruits such as figs, bananas, and mangoes, though a few instances of carnivory have been noted. Females tend to travel a consistent route to find predictable fruits, whereas males travel more to find the highest quality fruit. It forages at night, sleeping during the day in tree roosts. Individuals may roost alone or in small groups. Unlike many other bat species that segregate based on sex, males and females will roost together during the day. It has two mating seasons each year during the dry seasons. It is believed to be the only bat species with a classical lek mating system, wherein males gather on a "lek", which in this case is a long and thin stretch of land, such as along a river. There, they produce loud, honking vocalizations to attract females. Females visit the lek and select a male to mate with; the most successful 6% of males are involved in 79% of matings. Offspring are born five or six months later, typically a singleton, though twins have been documented. Its predators are not well-known, but may include hawks. Adults are commonly affected by parasites such as flies and mites.
The hammer-headed bat is sometimes considered a pest due to its frugivorous diet and its extremely loud honking noises at night. In Nigeria and the Democratic Republic of the Congo, it is consumed as bushmeat. It has been investigated as a potential reservoir of the Ebola virus, with several testing positive for antibodies against the virus. It is not considered a species of conservation concern due to its large range and presumably large population size.
