July 3, 2007
Contact: Steven Hall
Sage Grouse Studies Available from University of Montana Researcher
Dr. Dave Naugle and other researchers from the University of Montana have released the results of three peer-reviewed studies on sage grouse and energy development in the Powder River Basin. The research included funding from the Bureau of Land Management, the State of Wyoming and the oil and gas industry.
"On the heels of Wyoming’s Sage Grouse Summit in Casper last week, the results of these peer-reviewed studies will help inform management decisions in Wyoming in the months and years to come," BLM Wyoming State Director Bob Bennett said. "The BLM encourages anyone interested in sage grouse to familiarize themselves with this important research."
The studies focus on sage grouse lek attendance and sage grouse and winter habitat use in coalbed natural gas development. The third study addresses West Nile Virus in sage grouse populations. The studies can be found at the Univeristy of Montana website: www.forestry.umt.edu/personnel/faculty/dnaugle/publications.htm. The studies will appear in future editions of the Journal of Wildlife Management and the Journal of Avian Diseases.
Findings of Dr. Naugle and other researchers within the PRB include:
Male lek-count data show the region-wide sage-grouse population declined by 84% from 1988-2005. In 1990-1995, severe population declines occurred prior to the onset of energy development. After the onset of CBNG in 1997, the pace of development increased rapidly. From 2001-2005, lek-count indices in CBNG fields declined by 82%, at a rate of 35% per year, whereas indices outside CBNG declined by 12%, at a rate of 3% per year.
Among leks of known status in 2004-2005, only 38% remained active within CBNG fields, compared to 86% of leks adjacent to or outside CBNG fields. The mean number of males per active lek was similar for leks in CBNG and outside CBNG in 2001, but averaged 45% (range 33-55%) lower for leks in CBNG from 2002-2005.
Findings show that CBNG development is having negative effects on sage-grouse populations over and above those of habitat loss caused by wildfire, sagebrush control, or conversion of sagebrush to pasture or cropland. Moreover, the extent of CBNG development explained lek inactivity better than power lines, pre-existing roads, or West Nile virus mortality.
Research findings show a lag effect, with leks predicted to disappear, on average, within 4 years of CBNG development. Intensive monitoring also allowed researchers to estimate the precise timing of lek disappearance relative to CBNG development. Regardless of other stressors, lek complexes did not go inactive until after CBNG development came into the landscape.
The current density of CBNG development (80-160 acre spacing) is 3-6 times greater than the level that sage-grouse can tolerate. Leks typically remained active when well spacing was = 500 acres (1.3 wells per section).
After controlling for habitat quality, research shows that sage-grouse in winter avoid sites that have been developed for CBNG. The birds are 1.3 times less likely to use otherwise suitable habitat once it’s been developed. Sage-grouse select for sagebrush flats but avoid rugged terrain and coniferous habitats.
Avoidance of CBNG in winter and the high likelihood of lek loss in spring threaten to severely impact populations along the Montana/Wyoming border where models classify only 13% of area as high quality winter habitat. Options are limited for these populations of non-migratory birds because they rely on the same landscapes to breed, raise broods, and survive the winter.
Undeveloped winter habitat is more abundant south and east of the city of Buffalo, Wyoming, than north along the border of Montana. Sagebrush here provides winter habitat for birds that nest as far north as 24 miles where winter habitat is poor. Unfortunately, the migratory nature of this population means that separate nesting and wintering grounds need to be conserved if this population is to persist.
West Nile virus (WNV) mortalities in radio-marked sage-grouse each year since 2003 (2-25% per yr) show that disease is a new and permanent stressor to sage-grouse populations. Mortality from WNV may have population-level impacts because female survival plays a vital role in population growth. Mortality events from WNV in 8 of 11 states since 2003 support the need to conserve the sage-grouse across their remaining range to spread the risk of impacts from disease.