Study: Wolf attacks impact calf weight
Calves don’t have trouble gaining weight in the vicinity of wolves unless one of the predators kills a member of their herd, according to an economic study.
There’s no evidence that calf weights are lower when a ranch property overlaps with the range of a wolf pack, according to University of Montana researchers.
“Once there was a confirmed wolf kill, however, there was an effect,” said Derek Kellenberg, an economics professor at the university and one of the study’s authors.
The study, “Crying Wolf?,” examined data about climate, forage conditions, wolves and other factors across 18 Montana ranches between 1995 and 2010.
The findings fail to substantiate the theory that the presence of wolves has a statistically significant impact on calf weight. Forage quality, rainfall and snowpack are much more important, the study said.
Calves that graze on a ranch property with a confirmed wolf kill, on the other hand, end up weighing about 3.5 percent, or 22 pounds, less than other calves, the study said.
“The wolf effect is relatively small but it is there for ranches that have confirmed wolf kills,” Kellenberg said.
It’s possible that a wolf kill may cause the cattle herd to “bunch up” or remain in areas they perceive as safe, reducing their access to quality forage, he said.
Cattle may spend more time scanning the horizon for wolves and less time eating, he said. Stressed cows may also produce less milk for their calves.
Kellenberg said these were just possibilities and were not tested in the study.
Wolf kills cost ranchers about $6,700 on average in calf weight, not counting the dead animals, the study said.
In these situations, ranchers are not merely “crying wolf” — the indirect losses would be in the hundreds of thousands of dollars for the Montana ranching industry alone, the study said.
“Oftentimes, we don’t fully understand the economic cost of that,” Kellenberg said.
Even so, the effect of weather variations outweighed the impact of wolf kills, as did the number of days calves spent on pasture, he said.
The study determined whether wolves were present on ranch properties based on sightings by state wildlife officials, as well as tracks and scat, he said.
Researchers controlled for such ranch-specific effects on weight as cattle breed, Kellenberg said.
Ranchers who used “range riders” to monitor for predators didn’t see a substantial improvement in calf weights, he said.
However, the study only came across a handful of ranchers who used this practice, which may have affected the results, Kellenberg said.
Hormone implants did increase cattle weights, but the researchers nonetheless saw a decline in this practice over time, likely for marketing reasons, he said.
The study backs up the observations of ranchers who believe “wolves have an impact aside from just the kill,” said Ryan Goodman, communications manager for the Montana Stockgrowers Association.
“We are encouraged to see the University of Montana do that kind of work,” he said.
The association, which helped pay for the study, hopes the findings will lead to further research on the physiological response that wolves provoke among cattle, Goodman said.
Steve Pedery, conservation director of the Oregon Wild environmental group, said the money used for the study “might have been better spent on assisting ranchers in implementing preventative measures to avoid conflict between the livestock and wildlife.”