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Swooping bats have big muscles


The more energetic a bat is as it hunts for food, the heavier its muscles are (Image: Science, Paul Bates)

Bats that hunt for food by swooping and turning have heavier muscles than bats that fly in straight lines, according to Australian researchers.

They say the link between the mass of flight muscles and the way bats forage for food could be used to help conserve endangered species worldwide.

Aeronautical engineer and bat enthusiast Bob Bullen, and field biologist Dr Norm McKenzie publish their research in the current issue of the Australian Journal of Zoology.

They looked at 29 of 35 species of bats in Western Australia.

But Bullen says the findings could be applied to all types of bats and would help conservationists worldwide mathematically define the needs of vulnerable species, especially habitat size.

"It is the first time we have been able to work out the engine size and fuel needs of bats so to speak," he says.

"We have your low-energy two-cylinder variety that toddle about, the general six-cylinders that go fast and then you have your high-energy powerful eight-cylinders."

The team weighed the chest, shoulder, back and upper arm muscles used in flight of non-pregnant or non-lactating bats and found flight muscle mass to be between 9% and 23% of the bats' total mass.

These muscles control the four basic wing functions, providing lift and thrust as the bats beat their wings: the downstroke, upstroke, flexing-extending at the shoulder and flexing-extending at the elbow.

The researcher learned that flight muscles mass directly relates to one of three foraging styles: low energy, general and high energy.

Arnold Schwarzeneggers of the bat world

High-energy foragers have a muscle-mass up to 60% greater than the average for bats. They used highly agile flight including tight turns at speed to catch insect prey.

Some high-energy foragers, like the dusky leafnosed bat or dusky horseshoe-bat (Hipposideros ater), can also hover for a few seconds using exaggerated wing motions to create lift.

Most bats fall into the general class and were larger, medium-speed flyers with moderate agility in the air to catch insects or slow-flying surface-foragers.

These include the western falsistrelle or western false pipistrelle (Falsistrellus mackenziei), named after co-author Norm McKenzie, and the white striped freetail or white striped mastiff bat (Tadarida australis).

Low-energy foragers have the lowest flight-muscle mass, the least energetic mode of flight and mainly foraged using steady-level flight. These include the northern freetail or northern mastiff bat (Chaerephon jobensis) and ghost bat (Macroderma gigas).

Tags: environment, biology, zoology