The ominous howl of the wolf has long been a source of fear and fascination for mankind. But new research shows they are not so different from people – for every wolf has its own distinct voice. By recording and analysing wolf howls, scientists have discovered a new way of identifying individual animals.
Holly Root-Gutteridge of Nottingham Trent University has developed sound analysis code that can tell which wolf is howling with 100% accuracy. Previously, pitch was used to tell wolves apart, but these only achieved an accuracy rate of 76%. Adding information about volume - or “amplitude” - to the code was key to increasing its accuracy, according to Root-Gutteridge.
“In humans, differentiating between voices of different pitch might allow us to tell the difference between, say, men and women. But by adding more information, we can differentiate more precisely between individuals,” Root-Gutteridge said. The same applies for wolves: the more information analysed, the more accurate the results.
All the better to see you with
The new code could prove very useful for monitoring wolves in the wild. Root-Gutteridge explained that there are currently three main methods for counting and locating wolves. Snow tracking involves waiting for snowfall then studying the footprints wolves leave in the snow. But this method has the disadvantage of being weather dependent.
Fitting wolves with GPS collars allows scientists to know the location of individual wolves via satellite signals. Unfortunately, this is an expensive exercise: “Each collar costs £2000 and you have to catch each individual wolf, tag it and release it back into the wild before you can start gathering data,” Root-Gutteridge explained.
“Another method researchers use is to go into the wild and howl at the wolves, then record their replies,” she added. “While this method is definitely the most fun, the results formerly had big error margins, as it was impossible to tell whether you were hearing the same wolf on different nights.” Now, Root-Gutteridge’s sound analysis code offers a way to reduce these error margins extensively.
What are they howling about?
Wolves howl for a host of different reasons. “Wolves use howling as a territorial defence, to help locate other pack members and also as a social activity: they seem to really enjoy it,” said Root-Gutteridge.
David Mech of the University of Minnesota added that howling seems to serve a “motivation function” in various circumstances. “After awakening, the wolves are logy [sluggish], but after a group howl, they rush off quite motivated,” he said. Mech also observed wolves howling to motivate their fellow pack mates. “I have several times seen a breeding female lure a sleepy mate off to hunt by howling and then return after the male is long on his way,” he said.
Wolves also appear to be very good at locating the origin of a howl. Mech recounted that when he howled at a group of wolves, they came to the spot where he had howled, even though they could not have seen him.
Mech said that in most areas, wolf populations are recovering from being endangered. But this is not the case for all species: populations of Maned, Ethiopian, Red, and Gray wolves are still endangered.
Lucy Tallents, an expert on Ethiopian wolves, was excited about the research. “For Ethiopian wolves, which are subject to pressures like rabies and habitat loss, it is critical to keep track of population sizes,” she said. “The best way of doing this is to count individuals.”
“Acoustic sensing is becoming much more popular in conservation, and it’s easy to see why,“ Tallents added. Methods like radio collaring and ear tags require the wolves to be caught, which carries a small risk of injury and can cause disruption to the pack’s activities. "Being able to identify individuals aurally would be really useful to us, and cause much less disturbance to the wolves themselves.”
The method can never give a definitive count though. “We can only ever detect a minimum number of wolves in a pack: if they are not howling, we won’t know they are there,” Root-Gutteridge said. “But the real revelation here is that we can now identify individual wolves.”
And the possibilities do not end with wolves. “Although the research has not been released yet, I have successfully used the method on other wolf subspecies and other canids.” Root-Gutteridge said. “Whether it’s wild dogs or coyotes; if it howls, we can analyse it.”