Roads have no effect on guanaco habitat selection at a Patagonian site with limited poaching

Abstract

Roads affect flora and fauna across the world. Large mammals are particularly vulnerable to road effects because their large home ranges lead to a higher probability of contact with road networks. Disturbance associated with roads can alter the probability of habitat use by making suitable habitat near roads inaccessible or underused. Many studies and monitoring programs for large mammals such as guanaco (Lama guanicoe) in South America, however, rely on counts made from roads to estimate population abundance and distribution. These counts implicitly assume that animal responses to roads are negligible, an assumption almost universally unstudied. We used density surface models with aerial survey data to evaluate the effects of unpaved roads on guanaco habitat selection, at the scale of the species' home range, in a Patagonian site with limited poaching. Contrary to expectations and regardless of disturbance level associated with roads, guanacos did not avoid roads at site (0.36 km2) or patch (2.4 km2) scales during any season. We posit two non-exclusive hypotheses to explain our results: (1) disturbance levels of roads are below thresholds of guanaco response, and (2) guanacos in our study area tolerated motorized vehicles due to limited harassment by poachers from roads. Our results, considered with opposite findings of strong road effects on guanaco at a landscape and regional scales, highlight the need to assess whether road surveys lead to biased estimates of ungulate abundance and distribution under different environmental conditions, human activities and scales of interest. Where long-term monitoring of large mammal populations relies on road surveys, aerial or other non-road surveys could be strategically conducted to determine whether counts from roads provide reliable estimates.