What NZ bats can teach us about old-fashioned romance

In a dating age dominated by the quick convenience of hook-up apps, New Zealand's only native land mammals have a thing or two to teach us about good old-fashioned romance.

In yet another fascinating finding about New Zealand's native bats - and yes, we do have them - the tiny species have shown females can size up a potential mate just from his ability to serenade her.

A new study reveals how lesser short-tailed bats rely on singing as a primary method of courtship - and the complex signals given out by males allow females to assess the physiological suitability of a mate.

The lesser short-tailed bat exists today in two sub-species - one considered nationally endangered and the other declining - but the greater short-tailed bat hasn't been seen since 1967 and is probably now extinct.

Capable of tucking away their wings so they can walk on their elbows and scuttle across the forest floor where they chase weta and forage for grubs, Mystacina tuberculata are also unique for being one of only two bat species that engage in what's called lek breeding - a term derived from the Swedish word for play.

Scientists have been amazed to watch how males find a suitable tree cavity, sing a tune - and sometimes pee on themselves to smell good.

Once a bat had lured a passing female and mated, they left the spot and another male came in - making the tree cavities something of a time-share apartment split between blokes.

These shared bachelor pads are generally spread out around trees that the bat populations rest in during the day.

In the new study, former University of Auckland researcher Dr Cory Toth and colleague Stuart Parsons of Australia's Queensland University of Technology recorded and analysed the tunes of 16 "lekking" males. They identified four distinct notes the male bats used as part of their efforts to attract a female - upsweeps, downsweeps, trills and tones.

These sounds were either uttered as single notes or combined into one of 51 distinct syllables.

On average, each male produced 29 syllables.

Four distinct syllables - a combination of trills, upsweep-trills, trill-downsweeps, or upsweep-trill-downsweeps - were especially popular and were used 69 per cent of the time.

Further, the males studied each had their own distinct, individual way of producing each of the four most popular syllables.

The males seldom fell silent during the course of the six hours they spent on average in the singing roosts.

Based on the researchers' calculations, a male could produce up to 100,000 syllables a night.

"Lesser short-tailed bats potentially have one of the highest sustained song outputs for either birds or bats that researchers know of," Toth said.

The length of the second most popular syllable that male bats produced - the trill-downsweep combination - was thought to contain very specific clues about the body size of the serenading males.

Larger males were found to utter significantly shorter trill-downsweeps, while those on the smaller side produce longer ones.

"The length of the trill-downsweep combination provides females with the opportunity to appraise male size by auditory clues alone," Parsons said.

"Our results suggest the singing displays of male lesser short-tailed bats are signals that provide useful, honest cues of male characteristics and identity to females, and are as complex as the songs of many bird species."

Although amazing, Toth said the discovery that male songs effectively encode information on male morphology and individual identity weren't not really surprising at all.

"As lek breeders, males do not use territory quality or resources to entice females to mate with them, and so it's useful for females to identify males by their songs alone and assess male characteristics," he said.

"Mystacina also have relatively long breeding seasons, and so individuality may help females track male performance across time, helping them make a decision on whom to mate with."

Toth and colleagues have learned much about the bats' behaviour over recent years - that they were lek breeders was only discovered in 2015 - but scientists had only scratched the surface.

"There are many more questions worth examining," he said.

"What specific parts of male songs are females selecting for when they choose mates?

"How are timeshare roosts formed, and how often do those males interact?"

All of it was important to find out - now more than ever - as rat plagues were rapidly sending the threatened species towards extinction.