Summary of findings, Holloran Upper Green River basin sage grouse study

STUDY BACKGROUND

The study considered sage grouse populations in the Pinedale Anticline and Jonah gas fields in Western Wyoming, as well as sage grouse in adjacent areas where development was not occuring. Of the 313 square miles of the Pinedale Anticline field, only 7.3 square miles (approximately 2 percent) remain unleased for oil and gas development.
The author’s findings suggest that “current development stipulations are inadequate to maintain greater sage-grouse breeding populations in natural gas fields” (page 57).

Impacts to Breeding Males

Populations of breeding males on leks (sage grouse mating sites) in areas subjected to full-field natural gas development in the Pinedale Anticline and Jonah fields declined by an average of 51 percent from the year prior to development to 2004, compared to only a 3 percent decline at undisturbed leks.
Males at three leks surrounded by natural gas development declined by 89%; two of the three leks were abandoned entirely within 3 to 4 years of initiation of gas drilling.
Active drilling within 3.1 miles of a sage grouse lek reduced the number of breeding males that used the lek.
After drilling and construction had been completed, the presence of producing gas wells within 1.9 miles of a lek site reduced the number of breeding males using the lek.
As road traffic increased, the number of breeding males on affected leks decreased.
As well densities increased, the number of breeding males on affected leks decreased.
Well densities of 1 or more wells per square mile reduced the number of males at affected leks.

Impacts to Nesting Females

Some 64% of sage grouse nested within 3.1 miles of a lek site.
Females showed strong fidelity to their nesting areas, and continued to nest in affected areas even after roads and wells were developed nearby. Older females remained in affected areas, while yearling females departed from gas fields.
Overall, females strongly avoided nesting in areas of high well density.
There was a 21 percent decline in the population of nesting females relative to undisturbed females over the 5 years of the study.
Females nesting in developed areas had a significantly lower survival rate than female grouse in undeveloped areas. Although nest success rates were higher in developed areas, this increase was not sufficient to overcome the lowered female survival rates, resulting in an overall 21 percent decline in sage grouse population growth in developed gas fields relative to undeveloped areas.
The study predicted that sage grouse populations would become extinct in the Pinedale Anticline and Jonah Fields within 19 years if current population trends continue. (Both of these fields are in the early stages of development. As impacts to sage grouse habitat become progressively worse with the planned increase in gas drilling, the population declines could become steeper in the future).
Population reductions likely result from a combination of dispersal away from gas fields and increased mortality rates for birds affected by development.