Maximizing the detection probabilities of dusky grouse for population monitoring

Abstract

Despite its status as a game species in the western USA, rigorous monitoring of dusky grouse Dendragapus obscurus populations is limited. Obtaining an adequate number of observations for effective population monitoring of dusky grouse is challenging due to difficult-to-reach montane habitats, cryptic behaviors, and limited personnel, time, and funds at conservation agencies. While habitat accessibility and survey effort constraints may be outside a manager's control, identifying the most effective protocols to better detect a target species is possible and will improve monitoring programs. Our objectives were to 1) evaluate field-based protocols for maximizing dusky grouse detections and 2) identify survey conditions and timing that maximize the probability of detecting dusky grouse in western Montana. We conducted replicated point-count surveys with and without electronic playback of grouse calls in spring and summer 2019, and spring surveys solely with electronic playback in 2020–2021. We used N-mixture models to compare the probability of detecting dusky grouse in spring versus summer sampling and evaluate the effects of electronic playback of grouse calls, route type (off-trail, trail, and road), weather, background noise, day, and time on probability of detection. Spring sampling yielded substantially more dusky grouse detections than summer sampling. The use of electronic playback of female sooty grouse calls in the spring increased detection probability but dusky grouse chick distress calls during the summer did not improve detection rates. The probability of detecting a dusky grouse was similar across the different route types (off-trail, trail, and road), and maximized on clear days, with little wind and background noise, with surveys occurring 9–162 min post-sunrise during 3–23 May. By examining the effects of different factors on dusky grouse probability of detection, our results provide necessary information for the development of effective protocols for field surveys for population monitoring of dusky grouse.