Bats hum for sugar too

Researchers report for the first time that some nectar-feeding bats metabolize sugar at the same frantic rate as hummingbirds do.

SUGAR FIX. Long-tongued bats hover like hummingbirds and rapidly convert sugar to energy to maintain their high-powered lifestyle. C. Voigt/Leibniz Inst., Berlin

Like hummingbirds, South American long-tongued bats (Glossophaga soricina) hover at flowers and feed on sugar-rich nectar. While other mammals, including people, convert sugars to glycogen and store it in body tissues for later use, the bats extract energy immediately from almost all the sugars. This “little metabolic trick,” says coauthor John Speakman of the University of Aberdeen in Scotland, was previously seen only in birds, such as the hummingbird, and not mammals.

In their tests, the researchers kept bats on a normal diet of nectar, which contains several sugars, but then abruptly switched to a dose of pure sucrose, fructose, or glucose. By measuring sugar-breakdown products in the animals’ breath, the team determined what percentage of exhaled molecules were from the old diet and what fraction came from the sugar that the bats had just consumed. The results indicated that the mammals began obtaining energy from the pure sugars within minutes of eating them.

In a separate experiment, the team found that a long-tongued bat burns almost 60 percent of its energy reserves each day. If the bat can’t replenish that store, it will have “a window of a couple of days” before it dies of starvation, Speakman says. “It shows how dependent these animals are on the stability of their environment.”

The findings appear online and in the October Functional Ecology.

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