Dr. Jeffrey L. Beck

Ecosystem Science and Management

Influence of Fall Harvest on Trends in Sage-Grouse Populations

Postdoctoral Research Associate: Jon Dinkins, PhD

The potential for negative effects on population growth from harvesting greater sage-grouse (Centrocercus urophasianus; hereafter “sage-grouse”) have been of concern to many groups in light of long-term population declines. These concerns have been amplified with the possibility of sage-grouse being listing as threatened or endangered under the Endangered Species Act of 1973. The 2010 U.S. Fish and Wildlife Service (USFWS) listing decision only provided general information about the influence of harvest on sage-grouse populations, but this listing decision did indicate that the highest harvest occurred in the 1970s, when over 200,000 grouse were harvested in 9 of 10 years, and has declined since, with an average annual harvest of approximately 31,000 birds from 2000 to 2007. The 2010 listing decision further indicated uncertainty about whether harvest is compensatory or additive to sage-grouse populations. Since the 1990s, the general trend for harvesting sage-grouse in the western United States has been to hold hunts later in September to avoid over harvesting females with broods before brood break-up, reduce bag limits, and shorten seasons. Many states now only issue permits to sage-grouse hunters through a limited entry draw process. Wings from hunter-harvested birds provide state agencies with useful information to calculate sex and age ratios for grouse populations, which are used to index population productivity through chick to adult (and yearling) female ratios. Our objectives are to evaluate the influence of fall harvest on population structure and trend as follows:

1. Effects of Harvest on Population Growth in Greater Sage-Grouse: Evaluation of the relationship of fall harvest level on spring lek attendance with reliable data (i.e., past 10–20 years). We will simultaneously compare annual weather (drought), seasonal weather (e.g., monthly precipitation, temperature, etc.), human disturbance (fragmentation), wildfire, and hunting to lek counts. This will allow for a comparison of relative effects.
2. Response of Greater Sage-Grouse Population Structure to Different Harvest Strategies: Do different harvest management strategies create different sex ratios for sage-grouse populations? Is season length or season timing (i.e., dates of season) associated with sex ratio of sage-grouse? It is generally thought that fewer brood hens will be taken by hunters during later hunting seasons. We will assess sex ratios from hunter surveys and wings from harvested birds collected in wing barrels to assess whether early hunting season dates mean proportionally more females and juveniles are harvested than males.
3. Response of Sage-Grouse Population Growth to Anthropogenic and Environmental Stressors under Different Harvest Scenarios: We will take what is learned from the past 10–20 years of harvest and lek data and simulate long-term population trends as a function of the effect of hunters under multiple 'hunting scenarios' while simultaneously evaluating anthropogenic development and drought. The 'hunting scenarios' may include (1) existing data from USFWS on harvest (categorized as high effort), (2) extrapolated hunter take/effort from 1995–end of study, (3) simulate 1970’s–80’s hunting years with current lower hunter effort, and (4) any other reasonably hypothesized category of potential hunting effort.