狼群捕食影响家畜体重的增长

A recent study by University of Montana faculty¹ and graduate students found that wolf predation of cattle contributes to lower weight gain in calves² on western Montana ranches⁴. This leads to an economic loss at sale several times higher than the direct reimbursement⁵（退还，赔偿） ranchers receive for a cow killed by wolves. The study found that wolves living on the landscape with cattle have no effect on herd⁶ weight, but once a ranch³ has a confirmed wolf kill, average calf⁷ weight decreases relative to if that ranch had not experienced a wolf depredation⁸.   "Ranchers have been saying for years that wolves cause weight loss in cattle, but nobody ever had done any research on the topic," said Derek Kellenberg, a co-author on the study and UM associate professor and chair of the Department of Economics.   Kellenberg worked with UM Associate Professor Mark Hebblewhite from the Wildlife Biology Program and graduate students Joseph Ramler and Carolyn Sime. The Montana Department of Fish, Wildlife and Parks also cooperated on the study, which analyzed⁹ data from ranches in western Montana, including 15 years of records on ranch husbandry（饲养，耕种）, satellite-generated climatological data, spatial¹⁰ data on wolf pack locations and confirmed depredations¹¹ on 18 ranches.   The study quantifies the economic impact of weight loss after a confirmed wolf kill for an average ranch consisting of 264 head of calves. It finds that a decrease of 22 pounds in the average weight of calves across the herd implies a $6,679 loss at sale for an affected¹² ranch.   "When you compare that to the direct reimbursement of the cow that was killed -- about $900 on average -- these indirect costs are about seven-and-a-half times the direct cost of depredation," Kellenberg said.   The study notes that while the economic impact of lower herd weights caused by wolf depredation is not insignificant¹³ to ranchers, other ranch-specific husbandry practices and climatological and environmental variables such as annual precipitation, average temperature and snowfall explain a much larger proportion of variance¹⁴ in calf weight over the years than do wolf affects. In fact, these other factors explain the vast majority of the accounted-for variation in annual calf weights.   The study started as a senior thesis by then-undergraduate student Ramler, collecting data from public cattle auction¹⁵ records. When he decided#p#分页标题#e#¹⁶ to pursue a master's in economics from UM, the group started collecting and analyzing¹⁷ data from a survey of individual western Montana ranchers.   Kellenberg hopes the study will help inform policymakers and ranchers as they work on issues related to wolf management.   "This study helps quantify some of the indirect costs that have not previously¹⁸ been accounted for," he said.