Tag Archives: fruit bat

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.

Researchers translate bat language. Turns out, they argue a lot

A new algorithm has analyzed fruit bat squeaks, and it came to the conclusion that they discuss with each other much like you and I do.

A baby Egyptian fruit bat. Image credits: Dawson / Wiki Commons.

The new study was conducted by Prof. Yossi Yovel of the Department of Zoology at the Tel Aviv University in Israel. He recorded the sounds emitted by 22 Egyptian fruit bats over the course of 75 days, creating a database of 15,000 vocalizations.

“When you enter a bat cave, you hear a lot of ‘gibberish,’ a cacophony of aggressive bat noise — but is this merely ‘shouting’ or is there information amid the noise?” said Prof. Yovel. “Previous research presumed that most bat communication was based on screaming and shouting. We wanted to know how much information was actually conveyed — and we wanted to see if we could, in fact, extract that information.”

The first thing they found was that the sounds aren’t random – it isn’t just a mixed up cacophony, there are discernible patterns for bat sound making. Researchers managed to group about 60% of all sounds into four categories, the rest of the 40% being yet unclear.

Most of the 60% are arguments. Most commonly, bats argue about food – this was the most common type of sounds. But bats also argue about their position in the sleeping cluster. Another type of argument was bats protesting that other bats got too close to them. Lastly, the fourth category represented┬ámales making unwanted mating advances – nature’s love spam. The success of the study surprised even the researchers themselves, who weren’t expecting to come across such a trove of valuable information. The researchers emphasized that aside from humans, only a handful of other species are known to┬áaddress individuals rather than making broad communication sounds.

“We generated a massive amount of data — dozens of calls over three months,” said Prof. Yovel. “We have found that bats fight over sleeping positions, over mating, over food or just for the sake of fighting. To our surprise, we were able to differentiate between all of these contexts in complete darkness, and we are confident bats themselves are able to identify even more information and with greater accuracy — they are, after all, an extremely social species that live with the same neighbors for dozens of years.”

Aside from helping us understand bats in a different light, the study could shed some light on communication itself. This type of study is becoming more popular and interesting with the development of machine learning. Complex algorithms can identify the patterns and split the sounds into groups which biologists can then interpret.

“Studying how much information is conveyed in animal communication is important if you’re interested in the evolution of human language,” said Prof. Yovel. “Specifically, one big unknown in the world of animal communication is their grasp on semanticity — i.e., when you hear the word ‘apple’ you immediately imagine a round, red fruit. We found, in our research, that bat calls contain information about the identities of the caller and the addressee, which implies that there is a recognition factor. We were also able to discern the purpose and the context of the conversation, as well as the possible outcome of the ‘discussion.'”

Continuing this study, they now want to figure out if this communication is something instinctive and bats are born with it, or if it is learned in a cultural fashion.

Journal Reference: Yosef Prat, Mor Taub, Yossi Yovel. Everyday bat vocalizations contain information about emitter, addressee, context, and behavior. Scientific Reports, 2016; 6: 39419 DOI: 10.1038/srep39419