Wolves make roadways safer, generating large economic returns to predator conservation

Abstract

Recent studies uncover cascading ecological effects resulting from removing and reintroducing predators into a landscape, but little is known about effects on human lives and property. We quantify the effects of restoring wolf populations by evaluating their influence on deer-vehicle collisions (DVCs) in Wisconsin. We show that, for the average county, wolf entry reduced DVCs by 24%, yielding an economic benefit that is 63 times greater than the costs of verified wolf predation on livestock. Most of the reduction is due to a behavioral response of deer to wolves rather than through a deer population decline from wolf predation. This finding supports ecological research emphasizing the role of predators in creating a "landscape of fear." It suggests wolves control economic damages from overabundant deer in ways that human deer hunters cannot.

Keywords: deer–vehicle collision; economic impact; gray wolf (Canis lupus); trophic cascade; white-tailed deer (Odocoileus virginianus).

Fig. 1.

Wolf packs spread across Wisconsin between 1980 and 2010. Wolf packs are concentrated in the forested areas in the northern and central parts of the state. The rest of the state is predominantly nonforested agricultural or urban areas.

Fig. 2.

Trends in wolf abundance, deer abundance, and roadway collisions. (A) Winter wolf population per 100 km² of deer range. Deer range is defined as permanent cover at least 4 ha in size in 1993, the only year available. (B) Prehunt deer population per km² of deer range. (C) Vehicle collisions caused by deer. (D) Vehicle collisions not caused by deer. (E) Percent of vehicle collisions caused by deer before and after wolves enter a county, 1988 to 2010. (F) Percent of vehicle collisions caused by deer regressed on indicator variables for years since wolf recolonization, county, and year, 1988 to 2010. SEs clustered at the county level. (E and F) Data exclude three counties with wolf exit at some point during the period.

Fig. 3.

Wolf presence reduces the frequency of DVCs through changes in deer abundance and behavior. (A) The “net effect” occurs through changes in both mechanisms. (B) The “behavioral effect” occurs through changes in deer behavior only. Subtracting B from A provides the “population effect,” which occurs through changes in deer abundance only. (A and B) Model 2 excludes three counties with wolf exit at some point during the period. Model 3 excludes 13 counties that never have wolf presence (nonwolf counties) on the boundary of counties that have wolf presence for at least 1 y during the study period (wolf counties). SEs clustered at the county level.