Survival of greater Sage-Grouse broods: Survey method affects disturbance and age-specific detection probability
Investigators rely on brood surveys to estimate annual fecundity of game birds. However, investigators often do not account for factors that influence brood detection probability nor rarely document how much females and their broods are disturbed (flush rates) during surveys, which could lead to biased survival estimates. We used 45 radio-tagged female Greater Sage-Grouse (Centrocercus urophasianus) with broods to compare detection probabilities and document disturbance among four survey methods to allow future investigators to select the method that best meets their objectives. These methods included daytime flush, daytime visual, nocturnal spotlight, and fecal surveys at nocturnal roost sites, with the latter being a novel method. We used Cormack–Jolly–Seber (CJS) models to compare detection probability and daily survival estimates for visual and fecal surveys of broods 0–47 d post-hatch and a double-survey approach to compare detection probabilities among flush, fecal, and spotlight surveys ~42 d post-hatch when investigators often determine brood fate. From CJS models, detection probability for visual surveys increased with brood age (0.618–0.881), whereas detection probability for fecal surveys did not (0.748). Daily survival probability estimates increased with brood age and differed annually based on fecal surveys (2016: 0.978–1.000 and 2017: 0.839–0.998). We detected age-specific daily survival probability with visual surveys (0.956–0.997), but not annual differences. Based on the double-survey approach, detection probability was high (0.857–1.000) for all methods. We flushed ~310–750% fewer females and broods during fecal and spotlight surveys than during both types of daytime surveys. Our results highlight the need to account for detection probabilities among methods and document disturbance to hens and broods that can help investigators design surveys to minimize impacts to birds. Furthermore, our result suggest that actions to improve brood survival during the first week post-hatch may improve local recruitment.
|Survival of greater Sage-Grouse broods: Survey method affects disturbance and age-specific detection probability
|Ian P. Riley, Courtney J. Conway, B. S. Stevens, S. Roberts
|Journal of Field Ornithology
|USGS Publications Warehouse
|Coop Res Unit Seattle