Abstract
Biologists use a variety of methods to estimate productivity and resource selection of birds. The effectiveness and suitability of each method depends on the study's objectives, but is also influenced by many important traits, including detection probability, disturbance of focal birds and sampling frequency. We reviewed 504 greater sage‐grouse Centrocercus urophasianus papers published from 1990 to 2019 to document the most common brood survey methods used by investigators and summarized if and how they used brood survey data to estimate brood survival and detection probability. Of the 504 papers, 16.1% (n = 81) had useful information relevant to the review. The most common methods included daytime visual surveys (46.9%; n = 38), daytime flush surveys (33.3%; n = 27), nocturnal spotlight surveys (19.8%; n = 16), radio‐tagged chicks (16.0%; n = 13), wing surveys (9.9%; n = 8), brood routes (4.9%; n = 4) and pointing dogs (4.9%; n = 4). Fifty‐nine of the 81 papers used >1 method, only 2 of the 81 papers measured or reported detection probability, and none reported the level of disturbance caused by the method. Studies varied widely regarding the age of the brood when brood fate was confirmed (x̄ = 44.4 days post‐hatch, range 14–84 days). The frequency of brood sampling visits also varied greatly among studies (range = 1.19–3.85 surveys/brood/week) and this variation complicates comparison in fecundity and survival estimates across studies. Furthermore, 35 papers used >1 maternal behavior as purported indicators of brood fate, but none of them documented how accurate their indicators were. Future studies could reduce variance in estimates of sage‐grouse fecundity and brood survival by employing empirical methods to estimate detection probability, standardizing brood sampling methods and conducting trials to document the effects of hen or brood capture, handling and flushing on brood survival estimates. Moreover, the accuracy of commonly used indicators of brood fate, including maternal behaviors, flocking behavior and distance moved after flush needs verification.
Highlights
Life history determines the vital rates of plant and animal populations and, measuring vital rates is essential for both basic and applied sciences
81 papers were useful for the review because they included brood survey methods used to estimate ≥1 vital rate associated with broods or chicks (Table 1): 47 journal articles, 31 graduate theses or dissertations and 3 book chapters
Among the 81 papers, the authors used field survey methods to: document brood habitat selection or space-use (54.3%; n = 44), estimate chick or brood success (43.2%; n = 35), estimate chick or brood survival (29.6%; n = 24), estimate an index of hen productivity and address life history questions related to hen productivity (7.4%; n = 6)
Summary
Life history determines the vital rates of plant and animal populations and, measuring vital rates is essential for both basic and applied sciences. Chick survival has a large influence on population growth rates in sage-grouse (Wisdom and Mills 1997, Taylor et al 2012) and, estimating chick survival, brood survival, and the factors that affect them (e.g. resource selection) will help guide conservation and management decisions (Dahlgren et al 2006, Atamian et al 2010, Guttery et al 2013, Coates et al 2017). The methods used to estimate chick and brood survival in sage-grouse and the habitat factors that affect those parameters are the same as those used for other gamebirds (Summers et al 2004, Steen and Haugvold 2009, Sands and Pope 2010, Dahlgren et al 2012, Orange et al 2016, Blomberg et al 2019) These methods (daytime visual and flush surveys, radio-tagging, nighttime spotlight surveys, pointing dog surveys and wing surveys; Dahlgren et al 2010a, Riley 2019) can potentially influence accuracy, precision and comparability among studies. To help guide future research and monitoring efforts on gamebirds, we conducted a thorough review of the methods used in past sage-grouse papers whose objectives were to estimate vital rates and habitat relationships related to sage-grouse chicks and broods
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