Tuesday, 20 October 2015

Straw-colored fruit bats: Ecosystem service providers and record-breaking flyers


When searching for food, African straw-colored fruit bats cover greater distances than any other bat species studied to dateDate:October 14, 2015Source:Max-Planck-Gesellschaft

African straw-coloured fruit bats fulfil important ecosystem functions by dispersing seeds and pollen during their flights. Researchers from the Max Planck Institute for Ornithology in Radolfzell together with colleagues from Ghana fitted African straw-coloured fruit bats (Eidolon helvum) with GPS-loggers to reveal the routes flown by the animals. Travel distances differed substantially according to season: during the dry season they covered up to 180 kilometres per night, while distances flown in the wet season was just one-third of this or less. This could be related to variations in population size during these periods. While the observed colony only consisted of a few thousand individuals during the wet season, in the dry season its population increased to over 100,000 bats. The more bats there are, the greater the competition food, and the further the animals have to fly to find sufficient food supplies.

Every evening as night falls in Accra, a colony of African straw-coloured fruit comes to life. "At first, just a few animals become agitated. Then more and more of them follow suit and a gigantic natural spectacle unfolds," enthuses Jakob Fahr, who headed the study. "You can almost set your watch by them."

The animals spend the days hanging upside down in the crowns of old mahogany trees. As soon as the sun sets, the time for resting is over and the entire colony embarks on its search for food: "When the fruit bats take off, the sky darkens" says Fahr. Every evening during the dry season, around 150,000 animals with a wingspan of up to 80 centimetres head off in all directions. They search for fruit and nectar before returning to their day roosts the following morning.

Straw-coloured fruit bats are among the most common bat species found on the African continent. These mammals live in colonies and exhibit pronounced migratory behaviour -- presumably due to the seasonal variations in food availability: depending on the dry or wet season, they gather in groups of up to several hundred thousand individuals -- as is the case in the Accra colony. At the beginning of the wet season, most bats leave Accra and migrate to northern savannas, leaving just a few thousand individuals behind.

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