Molecular scatology reveals diet secrets of New Zealand’s long-tailed bat

New Zealand researchers have analysed DNA in the poo of the long-tailed bat, revealing the endangered mammal’s true diet.

It feeds on aquatic insects like mayflies and caddis flies, which means that changes in water quality could threaten its survival.

The long-tailed bat (Chalinolobus tuberculatus) is one of only two bat species native to New Zealand, which are also the country’s only two terrestrial mammals. 

So beloved is the long-tailed bat that it famously won a popular vote for New Zealand Bird of the Year in 2021.

Yet University of Waikato Associate Professor Nicholas Ling says very little is known about the ecology of the microbat, which weighs less than 10 grams.

“It’s half the size of a mouse, it’s completely nocturnal. They fly very fast; about 60 kilometres an hour,” says Ling, who is lead author of the paper published in the New Zealand Journal of Zoology.

It’s these characteristics which make the bat challenging to research, an important task given the species is listed as nationally critical by New Zealand’s Department of Conservation.

Ling says the only way to understand what these bats are eating is by looking at their scats.

Earlier studies have relied on “literally dissecting poo and looking for fragments of wings and legs, and that sort of thing”, he says.

The new research pilots the use of a technique called ‘molecular scatology’. It’s a technical term for analysing environmental DNA in an animal’s poo to determine its diet.

“It worked extremely well,” says Ling.

“The surprising thing from the study was that the results were quite different to what people had found by literally dissecting the scats.”

This is because dissecting poo can only pick up on indigestible parts of an animal’s diet, things like fragments of wings and legs.

By analysing the environmental DNA in the scats and comparing these results to the DNA of individual prey species, scientists can reveal other sources of food which have been chewed and digested.

The analysis shows long-tailed bats are very dependent on aquatic insects like mayflies and caddis flies.

Ling says these types of insects are associated with a really good freshwater quality.

“What we’ve found is what we’ve kind of suspected. People who have looked at the ecology of these animals see that they mostly fly around sources of water like lakes, rivers and streams.”

It’s an important finding for the endangered species. 

Now the worry is if the bat’s food source is associated with good water quality, then modification of landscapes for urban development or agriculture – with flow on effects for water quality – does not bode well for the animal’s future.

The pilot study was a test to see if the molecular scatology approach would work. 

Given the team’s success, they now hope to expand their research to a more extensive study of long-tailed bats, as well as analysing the scats of New Zealand’s other bat species, the short-tailed bat (Mystacina tuberculata). 

The short-tailed bat is also threatened, and it might just be the “world’s laziest”, says Ling. 

“They are quite slow flying, and have relatively small wings […] they do a lot of their feeding actually on the ground. So, they’ll fly relatively short distances from their roosts and then drop down to the ground foraging.”