Wolf howl identification technology excites experts

22 July 2013 
By Michelle Warwicker BBC Nature

Which wolf is which? Experts may soon be able to monitor individual wild wolves by just their howls

Individual wild wolves can be recognised by just their howls with 100% accuracy, a study has shown.

The team from Nottingham Trent University, UK, developed a computer program to analyse the vocal signatures of eastern grey wolves.

Wolves roam huge home ranges, making it difficult for conservationists to track them visually.
But the technology could provide a way for experts to monitor individual wolves by sound alone.
"Wolves howl a lot in the wild," said PhD student Holly Root-Gutteridge, who led the research.
"Now we can be sure... exactly which wolf it is that's howling."

Watch rare footage of a coastal wolf fishing
See pups make an unusual appearance

The team's findings are published in the journal Bioacoustics.

Singing wolves
 
Wolves use their distinctive calls to protect territory from rivals and to call to other pack members. "They enjoy it as a group activity," said Ms Root-Gutteridge, "When you get a chorus howl going they all join in."

The team's computer program is unique because it analyses both volume (or amplitude) and pitch (or frequency) of wolf howls, whereas previously scientists had only examined the animals' pitch.
"Think of [pitch] as the note the wolf is singing," explained Ms Root-Gutteridge. "What we've added now is the amplitude - or volume - which is basically how loud it's singing at different times."
"It's a bit like language: If you put the stress in different places you form a different sound."

The scientists put their new tool to the test by studying dozens of archive recordings of wild eastern grey wolf howls, living mainly in Algonquin park, Canada, and collected by the British Library in London.

Their success rate was 100% when recognising individual wolves from their solo howls. And they achieved an accuracy of 97% when identifying wolves calling together in a "chorus howl".
Ms Root-Gutteridge said that the technology is in the last stages of development but she hopes it can be used by conservationists in the wild in the near future.

Howling facts

• A wolf howl can resonate over six miles.
• The low pitch and long duration of a howl is well suited for long distance communication in forest and across tundra.
• A lone wolf howls to attract the attention of its pack, while communal howling can act as a warning to rival packs to stay away.
• Wolves may simply howl to join in with other wolves.
• Wolves are able to recognise each other through the unique features of an individual's call.

• Watch wolves howling

"In scientific terms this is really exciting, because it means that if we hear a howl on one night we can tell if it is or isn't the same wolf that you hear on subsequent nights," she said.

Similar technology has been tested on captive wolf howls but this study is the first time such accurate results have been achieved from recordings taken from the wild, where varying conditions make recognition considerably more difficult.

Previously, an accuracy rate of 76% had been achieved by scientists using audio sampling to identify wild wolves.

"The two biggest challenges are getting 'clean' recordings... and sometimes the wolves just don't want to howl," said Ms Root-Gutteridge.

Experts have successfully used acoustic sampling to monitor other wild animals such as bats and marine mammals. Last week, scientists in Puerto Rico revealed audio technology that can recognise rainforest animals by the sounds they make.

Ms Root-Gutteridge speculated that her team's new vocal "extraction code" could be used in acoustic studies for "[other] wolves; coyotes; dogs. Anything that howls really."

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