Wolf kills of deer fawns near human infrastructure more dependent on deer movement than building density, study finds

The Greater Voyageurs Ecosystem (GVE) is an ecosystem in Northern Minnesota in which many studies of wolves have been done. That research continues today. The ecosystem boundary was set nut by any geologic or hydrologic landscape features, but in order to bound the study area and therefore the research efforts. Very few wolf packs live completely within the boundaries of Voyageurs National Park, which is set in the southern part of the GVE, and individuals in those park packs often wander outside the boundaries of the park throughout the year. When the study of wolves in the park began in the park, it was quickly understood that, in order to start to understand the factors that affect wolves, and how wolves work in the landscape, and in a boreal forest, the study area would need to be larger than the park and look at the full territories of the wolves that utilize the park. The size of the GVE, and its various land management techniques, also allow researchers to study how those differences impact wolves throughout the southern boreal ecosystem.

Sean Johnson-Bice from the University of Manitoba presented his study on wolves at the Great Lakes Wolf Symposium this year. This study was one that was done in Greater Voyageurs Ecosystem in Northern Minnesota. He wanted to determine whether wolves changed the frequency with which they preyed on fawns based on proximity to human habitation.

He and his research associates published a paper last year in The Journal of Ecological Applications regarding this study. They studied the cumulative effects of several different types of human activity had on kill sites of deer fawns. 

“Results of that study showed that wolves are predominantly killing and hunting deer fawns disproportionately within recently logged areas,” he told the more than 120 people assembled at the symposium. “We also found that kill sites and hunting locations were generally close to linear features such as roads and trails.”

He said it was also found that fawn deer kill sites occur closer to human infrastructure than he had originally predicted. Generally, large carnivores are thought to avoid human infrastructure such as homes and buildings overall, even in rural communities. That said, Bice wanted to dig deeper into deer fawn kill sites near those structures.

His study looked at two resort towns in the study area. He overlayed a map of where kill sites were predicted and a map of actual kill sites. He found special clusters of kill sites around the town of Ash River. While this showed wolves killing deer fawns more often near those human infrastructure sites, it did not answer the question why, how they are killing fawns exactly, or what other effects human infrastructure may have on wolf predation behavior in general.

Bice said he could, however, draw some general conclusions. Previous research has shown that large carnivores tend to be more nocturnal when hunting near human infrastructure. They also tended to spend less time at the kill site under these conditions in previous studies. This means that they may also increase their kill rate in order to consume the needed amount of resources, moving on to another kill rather than consuming one completely. This is done, obviously, to minimize risk of contact with humans near that infrastructure.

He wanted to know whether wolves were making any of those adjustments in predation behavior near the towns in his study. The first question was whether wolves disproportionately hunted deer fawns at night near human infrastructure. The second question was whether they disproportionately killed deer fawns at night near human infrastructure. He predicted that they were, in fact, adjusting their behaviors to reduce interactions with people by hunting at night.

Next, Bice said, he wanted to evaluate whether wolves adjusted their handling time of fawn carcasses near human infrastructure. He also wanted to look at whether there was a difference in handling time, or time spent at a kill site, based on whether deer fawns were killed at night or during the day. He said the next step was to try to discern if these patterns were different from breeding wolves to subordinate wolves.

Results

Contrary to what Bice thought the study might find, the study showed that wolves did not shift their predation on deer fawns to be more nocturnal near buildings. Subordinate wolves, he said, showed no real pattern. Breeding wolves, however, tended to hunt farther away from buildings at night. 

The study also looked at building density, and whether that was a factor. In areas with high building density, Bice said, subordinate wolves did tend to hunt more nocturnally. Breeding wolves, he said, did not exhibit much of a pattern at all.

When it came to kill site patterns, Bice and his team looked at 663 fawn kill sites. Approximately 75% of those kills occurred between sunrise and sunset. It peaked in the early morning until about midday, and again in the early evening. However, his data did show a shift toward more fawns being killed at night when they were closer to human infrastructure. 

When subordinate wolves are near buildings, there is a higher probability that they will kill a fawn at night. As they get farther away, they are more apt to kill deer fawns during the day. Breeding wolves showed a somewhat opposite pattern, he said. That said, the increase in fawns killed near human infrastructure at night was likely attributable to subordinate wolves.

Bice said that his prediction that wolves would decrease their handling time of deer fawn carcasses when they got closer to buildings. However, he said, that was not necessarily true. He found that handling time tended to increase with proximity to buildings, but decreased as kill sites got farther away from buildings. There was also a large discrepancy of handling times between breeding wolves and subordinate wolves. He also found that handling time was not dependent on whether the kill was during the day or at night. He said he wanted to learn more about that portion of his research. 

While he expected to see more building-proximity variation in predation behavior, he also said that, with fawns being more active during the day, availability may dictate kill sites more than building density. Wolves may also be keying in on the behavior of the doe to figure out where the fawns were located. They found a strong overlap here in their data, meaning this was very likely the driver of fawn predation.

Beckie Gaskill may be reached via email at [email protected].