Quirks & Quarks

The secret to flight in birds and bats is not just wings, it's guts

Birds and bats share a commonality in their microbiome that may mean they carry lighter loads.

Birds and bats share commonality in their microbiome that may mean they carry lighter loads

The gut microbiome of this fruit bat was examined as part of a study. (Holly Lutz)

The gut microbiome of birds and bats may have evolved to enable both species to fly more efficiently.

A project that began as a study of gut microbiome patterns in vertebrates accidentally turned up something interesting about bats and birds.

The hamerkop is a wading bird found throughout Africa. (Holly Lutz)

Biologist Holly Lutz and her colleagues set out to look at the gut microbiome of flying animals. They hypothesized that the gut microbiome would be different from non-avian species, possibly to accommodate flight in some way.

Collecting lots of poop

For Lutz, this meant collecting and analyzing hundreds of fecal samples from bats and birds from a range of ecosystems. This involved rooting through forests, caves and cliffsides in the name of gathering about 400 samples of bird poop, and about 450 samples of bat poop. From these samples, she was able make gut microbiome comparisons across various species.

Holly Lutz on her way to collect hundreds of samples of bird and bat poop. (Holly Lutz)

This showed a few things. One is that bats and birds have strangely similar gut microbiomes, which is a surprise. And the other is that neither rely on their gut microbiome anywhere near as much as non-avian animals do.

Humans and many other animals rely on a rich and diverse gut microbiome for a range of things, including efficient digestion and maintaining gut health.

Lutz thinks that for flying animals, a heavy gut full of bacteria could makes flight more difficult. Also, having to keep that bacteria fed is expensive energetically. 

Noack's roundleaf bat is found in tropical Africa. (Holly Lutz)

Adaptations for flight

Instead of relying on a gut microbiome to help break down food, bats and birds have evolved in other ways to extract nutrients from food much faster. Both also produce digestive enzymes not produced by other animals. They also have a shorter gastrointestinal tract which allows for a faster movement of food through the gut.

The conclusion from this study is what Lutz calls a paradigm shift. Previous thinking suggests that bats should have similar gut microbiomes to their fellow mammals, but they don't. They conclude that the link between birds and bats in terms of gut microbiome is not their ancestry, but more to do with their lifestyle — an example of convergent evolution.

The splendid glossy starling was also included in the study. (Holly Lutz)

Written and produced by Mark Crawley

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