Meet the hammer-headed bat: the flying mammal with the head of a puppy

Most bat species have little rodent-like faces but the hammer-headed bat (Hypsignathus monstrosus) is in a league of its own. The odd-looking flying mammal has a super elongated face that has many who see pictures of it on social media question its very existence. Yet despite its larger-than-life appearance, the hammer-headed bat is very much real.

Credit: SARAH H. OLSON.

The hammer-headed bat, also known as hammer-headed fruit bat and big-lipped bat, is a megabat species whose range is distributed across the tropical forests of central Africa. It prefers lowland moist forests, riverine forests, and swamp forests, as well as mangroves and palm forests where it roosts in the trees.

With a huge wingspan of up to 38 inches (97 cm), the hammerhead is Africa’s largest bat. Its average body length, however, is a much more modest 10 inches (25 cm). Males are significantly larger than females. In fact, it is the males that grow the large head with enlarged rostrum, larynx, and lips that make the species so recognizable, while the females look like other fruit bats.

Unlike other bat species that segregate based on sex, male and female hammer-headed bats will together in groups from as small as four to as large as twenty-five.

Males and females have different foraging strategies, with females using trap-lining, in which they travel an established route with predictable food sources even if that food may be of lower quality. Males employ a far riskier strategy, traveling up to 6 miles (10 km) in search of particularly good food patches. When the bats find the food they like, they may nibble at the tree a bit before picking some fruit and carrying it away to another site for consumption.

Their breeding season lasts one to three months. These bats exhibit classical lek mating, meaning many male suitors will congregate at a site and engage in competitive displays and courtship rituals, known as lekking, to entice visiting females. To woo females surveying for prospective mates, the males make a peculiar calling sound.

Credit: SARAH H. OLSON.

“I’m simply awestruck by hammer-headed fruit bats (Hypsignathus monstrosus). Close-up any given feature, eye, fur, nose, ear, wing, or foot, is extraordinary. In hand, whiskers appear in patterns seemingly unique to each individual, and the nasal and lip folds of the adult males, like the one shown, provide a sculptural finish to the overall moose-head look. As we handle them to collect samples, they show distinct behaviors ranging from docile to teeth masher, hence the thick leather gloves. Functionally, as the largest fruit bats in Africa (males weigh in around one pound), they are flying seed dispersal machines, critical to equatorial forest health,” wrote Sarah Olson, an associate director of wildlife health at the Wildlife Conservation Society (WCS), in a 2018 blog post.

Credit: SARAH H. OLSON.

Olson and colleagues have been studying these rather elusive bats for several years in order to better understand their ecology and behavior. Perhaps this may prove vitally important too in the future, considering all the hardship from the pandemic still fresh in everyone’s mind.

The hammer-headed bat is only one of three species of African fruit bats that can become asymptomatically infected with the dreaded Ebola virus, although scientists have yet to establish if the species is an incidental host or a reservoir of the virus.

“Aside from threats to human health, this deadly virus is linked to massive declines in populations of western lowland gorillas in Congo and Gabon. Our job as scientists is to find a way to prevent Ebola outbreaks and help conserve these bats for future generations, one bat at a time,” said Olson.

This article was originally published in June, 2021.

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