Featured Image: Gray wolves are often radio-collared for wolf pack censuses, but using other methods could reduce the need for live-capture. (This image by Campbell William and the U.S. Fish and Wildlife Service is marked with Public Domain Mark 1.0.)
Source Article: Barber-Meyer, S. M. (2022). Can non-invasive methods replace radiocollar-based winter counts in a 50-year wolf study? Lessons learned from a three-winter trial. Wildlife Research. https://doi.org/10.1071/wr22001
Protecting the fiercest of canines
Wolves are striking symbols of the wilderness. Many people listen for their distinctive howls and watch the forests for a flash of gray fur and pointed ears. Despite having a historic range across most of the United States, wolf populations were greatly reduced during the early 20th century due to habitat and prey loss, as well as hunting campaigns. They have made a comeback in recent years, but most US populations are still listed as endangered under the Endangered Species Act. Because of this, many protected areas have programs to keep a close eye on wolf populations through annual censuses called wolf counts.
Wolf counts have historically been conducted by live-capture and radio-collaring methods, which allow researchers to track wolves as they move. For example, a long-term study in the Superior National Forest (SNF) in northeastern Minnesota has used aerial radiotelemetry since the late 1960s. With this process, researchers radio-collar a small number of wolves and use their reported locations to find them during helicopter flights. When the radio-collared individuals are found, the pilots can count the number of other wolves in the pack.
This method has been invaluable in maintaining accurate wolf censuses, which assist lawmakers and land managers in taking steps to protect the most vulnerable wolf populations. However, live-capture methods such as radio-collaring can cause stress to the animals, and occasionally injury to both wolves and biologists. Therefore, recent studies have investigated the use of non-invasive methods — techniques which do not involve live-capture of wolves — to replace or supplement radio-collaring methods.
How do non-invasive methods stack up?
To test whether non-invasive methods could potentially replace live-capture methods, scientists conducted another study in the SNF. They considered five non-invasive methods: aerial snow-tracking, ground snow-tracking, camera-trapping, genetic surveys, and reports from community scientists. In all cases, the researchers wanted to figure out each pack’s size and territory range. The effectiveness of these options was compared to the success of traditional radiotelemetry, with some methods being more informative than others.
Ground snow-tracking was the most useful of the five options, though it also took the most human effort. Two groups of two researchers each traveled through the study site on-foot and using trucks and snowmobiles. They looked for wolves or wolf signs (including tracks, scat, or sites where prey was killed). When possible, they estimated the number of wolves in the pack that left the signs, and followed tracks to locate packs for more accurate counts.
Camera-trapping also provided detailed information on pack counts and territory ranges. It required much less field effort, but required more data analysis than any other method. Over the three-winter study period, motion-activated cameras collected over 4000 images suspected to contain wolves, which all had to be inspected by researchers. These photos were most useful when they included a wolf which could be identified (by its markings, an injury, or a radio-collar), because this allowed the scientists to match the photographed wolves to a pack, and therefore estimate the pack’s range using photographs from multiple locations.
The third non-invasive method, aerial snow-tracking, is similar to aerial radiotelemetry. In both cases, helicopter flights are conducted over the study area, looking for wolves or signs of wolves. The difference between the two methods is that with radiotelemetry, researchers know the locations of the radio-collared wolves and use this information to guide the flight path. Overall, aerial snow-tracking provided information on wolves which were not radio-collared or which were located in areas not accessible to other methods. However, wolf sightings were infrequent, and therefore hard to rely on for determining wolf territories.
This project also used wolf reports from community scientists to back up information from other methods. Genetic information was also extracted from wolf scat. With enough good-quality genetic samples, researchers can use this information to identify individual wolves, allowing them to estimate how many wolves are traveling together. In other words, researchers could conduct pack counts without ever seeing the actual wolves! However, not enough samples were collected in this study to be used this way.
Multiple methods are superior in Superior National Forest
Information collected using non-invasive options during the SNF study was an insufficient alternative to radio-collaring. However, when researchers combined the data collected from both radio-collaring and non-invasive methods, they found that using both methods at once was better than using either alone. The pack counts were more precise than those in previous years, which only used radio-collaring. In addition, using non-invasive methods meant that trapping wolves for radio-collaring only had to be done every other year, instead of annually, which reduces the chance of injury for both wolves and researchers. As technology advances, methods of counting large animals will continue to be developed, which will aid researchers in monitoring wolf populations to help ensure the health and prosperity of one of the world’s favorite canines.