Prairie Grouse Population Trends and their Historical Drivers in the Nebraska Sandhills

Authors

Danielle BergerFollow

First Advisor

Dr. Larkin A. Powell

Second Advisor

Dr. John P. Carroll

Date of this Version

2020

Citation

Berger, D. J. 2020. Prairie grouse population trends and their historical drivers in the Nebraska Sandhills. Thesis, University of Nebraska - Lincoln, USA.

Abstract

The Nebraska Game and Parks Commission (NGPC) has monitored greater prairie-chickens (Tympanuchus cupido pinnatus) and plains sharp-tailed grouse populations (Tympanuchus phasianellus jamesi), collectively known as prairie grouse, since the 1950s using spring breeding ground counts. My research modeled long-term, species-specific spatial and temporal trends of prairie grouse abundance and potential environmental drivers in the Sandhills of Nebraska using NGPC’s historical monitoring data. Prairie-chicken populations have increased since the 1950s while sharp-tailed grouse populations have remained stable or slightly declined. These population trends arise in the context of a dynamic landscape. I created indices representing raptor predation and hunting pressure, cropland, hay and CRP acreage, cattle stocking rate, drought and winter severity, landscape-level factors known to influence prairie grouse populations via mechanisms supported in the literature. I used a Ricker population process model in a Bayesian state-space framework to explore the relationship between species-specific breeding ground count data and environmental covariates with a one-year time lag. I incorporated indicator variable selection into the model to determine which covariates most strongly influence population trends. The most competitive greater prairie-chicken model included negative density dependence (β = -0.003, SD = 0.000, BCI = -0.004 - -0.003) and a positive effect of increased precipitation during the previous spring (β = 0.046, SD = 0.021, BCI = 0.005 - 0.089) on population growth rates. The sharp-tailed grouse model that received the most support included negative density dependence (β = -0.005, SD = 0.001, BCI = -0.007 - -0.003) and a negative effect of increasing cropland acres (β = -0.084, SD = 0,041, BCI = -0.168 - -0.005). The effect of grazing was also strongly supported for both species. Although prairie-chickens and sharp-tailed grouse have traditionally been managed as a single species because of their similar resource needs, my findings suggest that prairie grouse conservation measures may be more successful if they are tailored to individual species. My study provides a framework for wildlife managers to use existing count-based monitoring records and free, publicly available environmental data to explore population drivers in addition to abundance trends.