Hammer-Headed Bat

## Description

The Hammer-headed bat is a large fruit bat found in Africa. Males and females greatly differ in appearance which makes 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. Males overall have boxy heads with enormous lips, while the females, with their narrower snouts, have more foxlike faces. Males and females both have dark brown fur, with a paler mantle (sides and back of neck). They have 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.

## Distribution

Hammer-headed bats are found 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. They inhabit lowland rainforest, swamp forest, riverine forests, mangroves, and mosaics of forest and grassland.

## Behavior

Hammer-headed bats are nocturnal creatures and sleep during the day in tree roosts. They may roost alone or in small groups and unlike many other bat species that segregate based on sex, male and female Hammer-headed bats will roost together in small groups of around four individuals. Occasionally, groups of up to twenty-five have also been documented. 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. During most of the day, bats sleep with their noses covered by their wings. Members of the same group show little interaction with each other: they do not "squabble", vocalize, or groom each other. Instead, at sunset, they groom themselves then set off independently to forage. 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 of 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. Upon finding suitable fruit, Hammer-headed bats may eat at the tree or pick the fruit and carry it away to another site for consumption. They chew the fruit, swallowing the juice and soft pulp, before spitting out the rest.

## Diet

Hammer-headed bats are frugivores. Figs make up much of their diet, but mangos, bananas, and guavas may also be consumed.

## Reproduction

Hammer-headed bats are polygynous meaning that males mate with more than one female. Their breeding season lasts 1-3 months and occurs from June to August and from December to February. These bats exhibit classical lek mating and are perhaps the only bats with such. Males gather in a particular region, known as a lek and there they establish "display territories". These leks are usually formed along streams or riverbeds and consist of 20-135 males. Each male claims a display territory of about 10 m (33 ft) in diameter, in which he honks repeatedly and flaps his wings while hanging from a branch. Males display for around four hours before foraging, with peaks in lekking activity in the early evening and before dawn. Females will fly through the lek, selecting a male by landing on a branch next to him and the chosen male emits a "staccato buzz" call. After mating, the female immediately departs, and the male resumes displaying. However, some populations of Hammer-headed bats in West Africa do not use leks. Instead, they have a harem system. Females may become pregnant up to twice per year, giving birth to one offspring at a time, though twins have been reported. The gestation period lasts around 5 or 6 months. Newborns weigh approximately 40 g (1.4 oz) at birth. Males do not assist females in caring for offspring. Females reach reproductive maturity faster than males; they can reproduce at six months and reach adult size by nine months of age. In contrast, males become reproductively mature when they are eighteen months old.

## Population

### Population threats

The biggest threat to Hammer-headed bats is habitat destruction. They are also persecuted as pests due to their frugivorous diet and their extremely loud honking noises at night. In Nigeria and the Democratic Republic of the Congo, these bats are hunted and consumed as bushmeat.

### Population number

According to IUCN, the Hammer-headed bat is locally common and widespread throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List.

### Ecological niche

Due to their frugivorous diet Hammer-headed bats are important seeds dispersers in their ecosystem and they also serve as a food source for some birds of prey.

## Fun Facts

The Hammer-headed bat is the largest bat in mainland Africa.

The tongue of the Hammer-headed bat is large and powerful, with an expanded, tridentate tip. The tongue has backward-facing papillae which help to extract juice from fruits.

There have been anecdotes of the Hammer-headed bats killing and eating chickens, or consuming scraps of meat from bird carcasses left by humans. However, they are completely frugivores.

During the mating season male Hammer-headed bats have to try hard in order to attract females; they typically display for around 4 hours and produce 60-120 honks per minute.