Hummingbirds get some energy the easy way: passively

When it comes to energy metabolism, hummingbirds are the heavyweight champions of vertebrates. Pound for pound, the thumb-sized birds have higher energy demands than elephants.

For this reason, scientists have long studied hummingbirds to study energy balance. Till now researchers believed that the birds expend energy moving sugar molecules from the gut to the bloodstream. Wildlife ecologist Todd McWhorter has shown that that is not always the case.

Nutrient absorption occurs in the small intestine, after the stomach has digested food. In an energy-intensive process, cells lining the intestine actively move nutrients to the bloodstream.

But at the same time, McWhorter found, more than half of sugar molecules can also slip between the cell layer of the intestine and move straight into the bloodstream, using no energy at all.

The findings may change current thinking on how nutrients are absorbed in other vertebrates.