Never let go of your branch before grabbing another

by Amelaïd Houmadi and Kitty Brayne

They're among the biggest flying mammals in the world, found on two small islands in the Comoros archipelago in the Indian Ocean, and nowhere else in the world. In the Comorian language they are sometimes called m’lamanga which means mango-eater (but also have two other names: n’tréméla or ndéma), but it was from the explorer Dr Livingstone that they got their name with which they are known to the rest of the world. I'm talking about Livingstone's fruit bats, and at the moment it's my job to study them with the ECDD project in Anjouan.

They're fascinating animals. When they soar across the forested ravines, you could almost imagine they were pterodactyls – their wingspan can reach up to 1.4 metres! They're social creatures who spend most of the day hanging from a branch in large communal roosts. The bats' behaviour up in the trees has inspired two Comorian sayings: “Never let go of your branch before grabbing another”, and “Don't worry about me if I sleep upside down, worry if your husband has a mistress”.

Livingstone's fruit bats feed on the fruit, flowers and nectar of forest trees, and so potentially play an important role in forest regeneration, pollinating flowers and spreading seeds. As they are assumed to be dependent on intact forest, they will likely be an indicator species of forest health.

In the 1990s, it was thought there were only around 200 individuals left, prompting Bristol Zoo and Jersey Wildlife Preservation Trust (now Durrell) to organise missions to collect individuals for captive breeding programmes. Since then, more roosts were discovered and the current population estimate stands at 1,200 individuals, but they are still highly threatened as their forest habitat is under considerable pressure due to a rapidly growing human population with a shortage of fertile land for agriculture.

We've just completed a pilot study to test different research methods for a study of all 17 roosts in Anjouan. Our aims are to obtain a current population estimate for the island, compare roost counts with those done over 5 years ago, and assess changes in land use surrounding the roost sites.

It's hard work. The roosts are a long way from Mutsamudu, the capital of the island where the project is based. It takes two hours on a winding road to get to the closest village, and after buying supplies for the day we attack the mountain. Don't forget to bring water! With the sun and the heat, we're quickly soaked with sweat and it's nearly a two hour climb to get to the roosts. But the birdsong all around and the beautiful scenery keeps us going. For the last bit of the climb, we're no longer on a path, but scrambling through the forest, hanging on to lianas and shrubs so as not to fall.

Finally we’re greeted by the sight (and sound) of over forty fruit bats spread across a couple of trees. For this pilot study, we're monitoring the comings and goings of the bats over the whole day, to test when the best time to count them is to get the best estimate of the roost population. Also, we're surveying the surrounding habitat and state of the forest to compare between sites.

As this is just a pilot, we can't yet make any conclusions, but the initial signs are not great. The owners of the land where the roosts are found told us that they've noticed the number of bats using the roosts has decreased, and my colleague Ishaka who worked on previous studies of this roost has noticed that the surrounding habitat has changed; it’s alarming to see crops such as bananas planted under roosts were there was no plantation during previous studies.

The full study starts in December when the rainy season is in full swing. We’ll let you know how it goes!