Survival of Greater Sage‐Grouse broods: survey method affects disturbance and age‐specific detection probability

Abstract

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.

Effects of large‐scale disturbance on animal space use: Functional responses by greater sage‐grouse after megafire

“…We monitored the movements of all females, conducted flush surveys at 42 days posthatch (Riley et al, 2021 ; Riley & Conway, 2020 ) for females that hatched successful nests, and considered the brood successful if a female had at least one chick during the survey. We used PTT location data from females with successful broods to assess space use during the brood‐rearing period ( n = 67 females with successful broods from 2015 to 2020).…”

Estimating survival and adoption rates of dependent juveniles

“…A common goal of basic and applied research is to identify vital rates important to fitness and the persistence of populations. Understanding how a species' life history has evolved can assist investigators when predicting how populations will respond to changing environments (Cooch et al, 2001 ; Doherty et al, 2004 ; Rotella et al, 2012 ). In a given species, some life‐history traits evolve to be robust to environmental variation (Boyce et al, 2006 ; Pfister, 1998 ), whereas other traits evolve to be plastic in the face of environmental variation (Koons et al, 2009 ).…”

“…For long‐lived species with slow generation times, variation in adult survival is generally minimal compared with the variation in reproduction (Rotella et al, 2012 ). If finite population growth rate for phenotypes is a reasonable surrogate for fitness, population matrix models allow researchers to explore hypotheses about selective pressure on life‐history strategies (Caswell, 2006 ).…”

“…Estimation of juvenile survival has been hampered by three main constraints (1) chicks are too small to uniquely mark without affecting survival (Davis et al, 2016;Gregg & Crawford, 2009); (2) chicks cannot be detected with a probability of one (Gibson et al, 2016;Riley & Conway, 2020;Riley et al, 2021); (3) brood amalgamation makes it impossible to follow unmarked or marked chicks through space and time, even when the identity of the attending parent is known (Dahlgren et al, 2010). Marking chicks requires capturing them and often, performing surgery to implant or attach the transmitter with sutures, resulting in uncertainty about whether death in the first days of life was due to the handling process or environmental factors (Burkepile et al, 2002;Dahlgren et al, 2010;Davis et al, 2016;Gregg & Crawford, 2009).…”