Every wolf howls with its own “voice”and that’s how researchers are identifying non-radio-collared pack members.

Photo credit Angela Dassow

Identifying individual gray wolves by use of radio-tracking has been used for many years. Because wolves are rarely seen this is one of the main ways biologists have used to monitor them. The collars are used to monitor gray wolves, are also known as radio telemetry. They weigh around a pound, and have a transmitter on them that emits a signal on a specified frequency or channel. A biologist uses a special receiver and an antenna dialed to the specific channel signal being transmitted by a collar to locate the wolf. But this method for monitoring wolves has its drawbacks. Wolves can be injured in the process of capturing to fit them with a collar. There is another method and it’s very promising not to mention less invasive for the wolf. It’s been studied in Wisconsin’s central forests and the researchers are working to finely tune Acoustic Monitoring.

Every wolf howls with its own “voice.”

Angela Dassow

Biologists learn a great deal through use of radio-collaring

Some radio collars will emit different types of signals, if the wolf is active, the beeps might become more rapid. Most collars are equipped with a mortality signal, the one signal biologists hate to hear. It only comes on when the collar has not moved for several hours, and means the wolf is no longer wearing the collar or the wolf has died.

How do biologists catch a wolf and fit them with a radio collar?

This is where it can get tricky because biologists use cable foot snares to catch and restrain the wolf. This method can be invasive as well causing injury at times. The restraint is a long cable type rope with a grappling hook attached at the end. Once the wolf takes the bait, the foot hold trap is sprung, as the wolf moves the grappling hook wraps around bushes to hold the wolf in place. The idea behind the grappling hook is that the wolf is “gently caught” because it allows him/her to move. But can this method of trapping cause injury to the wolf?

A U.S. Fish and Wildlife Service employee fastens a radio collar onto a sedated female gray wolf. Lori Iverson/USFWS, CC BY

USGS performed a study “Evaluating Trapping Techniques to Reduce Potential for Injury to Mexican Wolves.” The following is some of the results.

“There was considerable variation in the severity of injuries sustained from the use of different foot snare models when they were tested on coyotes. Onderka and others (1990) tested two types of foot snares,
one of which produced injuries similar to that of an unpadded foothold trap, with the other model causing injuries similar
to a padded foothold trap.”

These methods for catching wolves in order to fit them for radio collars are being evaluated all the time for improvement and safety. That’s because there’s so much data and research gathered from the collars, and how it helps to mitigate human and wolf conflicts. But is it safe for the wolf? For instance, once the wolf is caught in the trap, they are given a knock out drug. Even though the wolf is knocked out, temporarily paralyzed, they are awake. The wolf can see and hear everything that is being done to them. Biologists try to do the least amount of harm to the captured wolf by working as safely and as quick as they can. They take blood and hair samples and weight the wolf, and they put on a blinder to protect their eyes, as well doing temperature checks. While knocked out the wolf cannot regulate their body temperature and the biologists have ice packs on hand to help keep them cool. Biologists put on the collar and finally administer the wake up drug. Trained biologists make sure they don’t keep the wolf knocked out very long and check them for any injuries sustained by the leg hold snare before releasing them back into the wild.

As I’ve stated this method of monitoring individual wolves has been used for many years, and it does help biologists learn more about this species. But is there another way to monitor individual wolves that is less invasive? As it turns out the answer is yes there is another less invasive method for monitoring individual wolves. An article in The Conversation, dated July 13, 2018, “Scientist at work: Identifying individual gray wolves by their howls” explains how scientists are studying individual wolves by their howls. The following is from one of the researchers Angela Dassow, Assistant Professor of Biology, Carthage College.

The traditional way to track wolves involves setting traps, sedating and then radio-collaring individual animals. While effective, this approach is time intensive and expensive, and entails risks for the animals.

I was fortunate to participate in this entire process firsthand as an undergraduate student. During the summer trapping seasons, I became familiar with each of the wolves in the central forest region of Wisconsin. This experience led to several conversations with the wildlife biologists in the area about whether wolf howls could be used to help identifying non-radio-collared pack members.”

This question remained a fun thought experiment for many years. Now as a biology professor who specializes in bioacoustics, I’ve been able to turn that thought experiment into a full research question: Can we use acoustic features to identify individual wolves in the wild?Angela Dassow, Assistant Professor of Biology, Carthage College.

Listen to a lone wolf howl.

Angela Dassow and Cara Hull survey a road in central Wisconsin for signs of wolves. Caitlin McCombe, CC BY-ND

“In 2013, behavioral ecologist Holly Root-Gutteridge and her colleagues successfully demonstrated that they could identify individual wolves in captivity using acoustic features. Their research provided evidence that it made sense to test whether vocal identification in wild animals is possible.”

“So with the support of the Summer Undergraduate Research Experience at Carthage College, volunteers from the Timber Wolf Information Network, and wildlife managers at Sandhill Wildlife Area in Babcock, Wisconsin, my undergraduate students Cara Hull and Caitlin McCombe and I began to record wolves in the wild.”

“It would be an understatement to say fieldwork can be challenging. On any given day, there can be daunting weather fluctuations. Biting insects, especially mosquitoes and deer flies, are abundant in wolf habitat. We had to constantly check ourselves for ticks. And then of course comes the actual fieldwork.”

Here’s what they discovered…

“We were able to isolate 21 howls from two adult wolves over two evenings. For each howl, we made six types of frequency measurements and two types of duration measurements. Frequency is how high or low the pitch of the howl sounds and duration is the length of time the howl lasted.”

“For wild gray wolves, we found that the maximum frequency – that is, the highest sound an animal produced – and the frequency at the end of the howl were the two variables that were most individualistic. For captive wolves, it was different. The lowest frequency an individual produced – what in acoustics is called their fundamental frequency – and the loudness of its calls were the factors that best differentiated among the captive individuals.” You can read Angela Dassow’s full article in The Conversation.

This method is promising and definitely less invasive than radio collaring. While radio-collaring could still work in some cases, vocal identification is a less invasive alternative for monitoring individuals because they eliminate any possibility of accidentally injuring an animal in a trap. The researchers will need to gather a database of positively identified individual wolves. The researchers say they can use remote monitoring stations to record howls, thus reducing the amount of time spent conducting nightly surveys. Acoustic monitoring could potentially track all the wolves in multiple packs whereas radio-collaring is typically used to track a single member in select packs according to the researchers.

You can read Angela Dassow’s full article in The Conversation.

Professor Angela Dassow received her B.S. degrees in wildlife ecology and entomology from the University of Wisconsin-Madison in 2003. After spending several years as the head preparator and assistant curator of herpetology at a natural history museum, she joined Prof. Michael Coen’s lab and earned her M.S. in zoology in 2010 and Ph.D. in zoology in 2014. She joined the Carthage faculty in 2015.

Prof. Dassow’s research focuses on computational analyses of animal vocalizations, exploring correlates with human linguistic phenomena at the phonetic, morphological, and syntactic levels. This work has centered on understanding the vocal communication systems of wild and captive white-handed gibbons (Hylobates lar); however, she has examined other species as well, ranging across a variety of taxa including cetaceans, bats, canids, and song birds. By combining aspects of ecology, linguistics, computer science, and information theory, we are able to gain new insights into the communicative abilities of white-handed gibbons and demonstrate previously unrecognized complexity and structure in their vocal communication system.

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