Greater sage-grouse population dynamics and probability of persistence

Publication Type:

Report

Authors:

Garton, Edward O.; Wells, Adam G.; Baumgardt, Jeremy A.; Connelly, John W.

Source:

Issue Final Report to Pew Charitable Trusts, p.90 (2015)

Call Number:

U15GAR01IDUS

URL:

http://www.pewtrusts.org/~/media/Assets/2015/04/Garton-et-al-2015-Greater-SageGrouse-Population-Dynamics-and-Persistence-31815.pdf

Keywords:

Centrocercus urophasianus, Greater Sage-Grouse

Abstract:

The authors updated their earlier comprehensive analysis of Greater Sage-Grouse (Centrocercus urophasianus) population dynamics and probability of persistence from 1965 to 2007 throughout the species range by accumulating and analyzing additional counts of males from 2008 to 2013. A total of 89,749 counts were conducted by biologists and volunteers at 10,060 leks from 1965 through 2013 in 11 states occupied by Greater Sage-Grouse. In spite of survey effort increasing substantially (12.6%) between 2007 and 2013, the reconstructed estimate for minimum number of breeding males in the population, using standard approximations for missing values from Colorado, fell by 56%, from 109,990 breeding males in 2007 to 48,641 breeding males in 2013. The best model of annual rates of change of populations estimated across the Sage-Grouse Management Zones was a stochastic density dependent Gompertz model with 1-year time lags and declining carrying capacities through time. Weighted mean estimates of carrying capacity for the minimum number of males counted at leks for the entire range-wide distribution, excepting Colorado, were 40,505 (SE 6,444) in 2013 declining to 19,517 (SE 3,269) in 30 years and 8,154 (SE 1,704) in 100 years. Starting with the estimated abundance of males counted at leks in 2007, a simple effort to evaluate the validity of future forecasts of abundance was conducted by forecasting abundance in 2013 from Gompertz density dependent models with 1-year time lag and declining carrying capacity models of 6 of the 7 management zone populations. Estimated mean abundance in 2013 predicted 97.8% of the variation in true abundance in management zones. Concerted efforts across both public and private land ownerships intended to benefit Greater Sage-Grouse show little current evidence of success, but more will be required to stabilize these declining populations and ensure their continued persistence in the face of ongoing development and habitat modification in the broad sagebrush region of western North America.