Context. Guanacos, the only native ungulates inhabiting Patagonian arid lands, are perceived by local people as a threat to livestock production and, consequently, uncontrolled hunting and harassment are widespread across the region. In 2005, a traditional sheep ranch (RSP) was converted into a wildlife reserve, offering the opportunity to assess changes in guanaco tolerance to motorised vehicles after harassment ceased.

Aims. The aims of the present study were to address factors influencing guanaco flight response on RSP, to assess inter-annual variation in flight responses after management changed and to compare guanaco response to cars among the RSP population, neighbouring ranches with traditional management and a southern population (C2B) that has had effective protection since the early 1970s.

Methods. Field surveys using available roads at RSP were conducted during a 4-year period to assess inter-annual changes in guanaco flight probability. Current estimates of flight probability at RSP were then compared with point estimates obtained from neighbouring ranches and the C2B population.

Results. We found that flight probability at RSP decreased as groups were located farther from the transect line and groups with at least one juvenile were more likely to flee than were adult-only groups. Flight probability decreased progressively during the study and significant differences with initial conditions emerged during the fourth year of monitoring. The current flight response observed at RSP is consistent with an intermediate state between neighbouring ranches and C2B population.

Key conclusion. Our results support the hypothesis that guanacos can become rapidly habituated to vehicles if harassment ceases and subsequent traffic acts as a neutral stimulus for enough time.

Implications. Finally, we discuss how our results may be helpful for other recently created reserves and ecotourism oriented projects.