Experimental effects of hiking on breeding Mexican spotted owls

On the Colorado Plateau, some environments occupied by Mexican Spotted Owls (Strix occidentalis lucida) receive a great deal of recreational use. To assess the effects of hikers on breeding owls, we quantified changes in the activity budgets of owls at nests in response to a controlled amount of hiking in canyons of southern Utah in 1997 and 1998. We examined differences in the duration and frequency of eight behaviors as well as in the type and frequency of owl vocalizations between hiking and control treatments. In general, activity budgets of owls did not change markedly when hikers were near nests, although during hiking treatments, females decreased the amount of time they handled prey by 57% and decreased the amount of time they performed daytime maintenance behaviors by 30%. Further, hikers caused both females and males to increase the frequency of contact vocalizations by 58% and 534%, respectively. The order in which we applied treatments at nests (control-hiking or hiking-control) also influenced owl responses to hiking treatments, suggesting that observers near nests may have affected owl behavior. We concluded that the cumulative effects of high levels of short-duration recreational hiking near nests may be detrimental to Mexican Spotted Owls. Given current levels of visitation rates to most remote canyons occupied by owls, however, owl populations on the Colorado Plateau are not likely threatened by hiking. Notable exceptions are those canyons that receive use by ≥50 hikers per day. We recommend monitoring of owl occupancy, nest success, and hiking intensity in these high-use canyons.