Life on an engergetic knife edge could render bats endangered

Nectar-feeding bats burn sugar faster than any other mammal on Earth - and three times faster than even top-class athletes - ecologists have discovered.

Glossophaga soricina with pollen from tree Palo Verde National Park, Costa Rica. Picture credit & copyright: "Dr. Christian Voigt"

The findings, they say, illustrate that because they live life on an energetic knife edge, these bats are very vulnerable to any changes in their environment that interrupt their fuel supply for even a short period.

Working with a captive breeding colony in Germany, Dr Christian Voigt of the Leibniz Institute for Zoo and Wildlife Research in Berlin and Professor John Speakman of the University of Aberdeen fed long-tongued bats (Glossophaga soricina) sugar labelled with non-radioactive carbon-13 and then measured the amount of carbon-13 in the bats’ exhaled breath.

Professor Speakman said: “We found that nectar-feeding bats made use of the sugar they were drinking for their metabolism within minutes after drinking it, and after less than half an hour they were fuelling 100% their metabolism from this source. For comparison, the highest rates reported in humans are for athletes who can fuel up to 30% of their metabolism directly from power drinks.”

The reason for this, say the researchers, is that they feed on floral nectars that contain simple sugars such as sucrose, glucose and fructose, but which are produced in only very small amounts by flowering plants. These sugars are rapidly absorbed and digested, and by metabolising them directly - rather than converting them to fat or glycogen and then using them up later - the bats get the maximum energy they can from the sugars.

“All animals need energy to power their metabolism. Ultimately this energy comes from food, but usually only a small fraction of the energy being used comes directly from the food. Normally, most of the food is converted into storage and this is drawn on later to fuel metabolism. Small nectar-feeding bats have among the highest metabolic costs among mammals, and mostly eat a diet low in fat and protein but rich in sugars. Metabolising these sugars immediately they are consumed saves the costs of converting them to and from storage,” said Professor Speakman.