During drought, sagebrush plants produce fewer stems, leaves, and flowering shoots, resulting in a smaller canopy coverage. Drought can reduce perennial grass and forb production and result in smaller insect populations. Both forbs and insects are of dietary importance to sage-grouse during brood rearing. During dry years, sage-grouse shift to wet meadow areas earlier in the summer and may switch to a sagebrush diet earlier in the year. Reduced forbs and insects and higher amounts of sagebrush in chick diets have been linked to lower chick survival.
Across the range of the bird, populations have cycled in relation to precipitation, with sage-grouse populations declining with below-average precipitation. However, other climate variables also influence sage-grouse populations, including the timing of precipitation and temperatures. Declines in the minimum spring population estimate also coincided with drought conditions in the late-2000s. For example, spring precipitation in 2007 was 60 percent of average, and the minimum spring population estimate in 2008 dropped 37 percent from approximately 24,900 birds in 2007 to 15,800 birds in 2008.
In Oregon, the effects of drought can be inferred from demographic parameters (age structure, sex ratios, nest success, and chicks per hen ratios) determined from plumage characteristics of wings voluntarily submitted by hunters who harvested sage-grouse. In 2014, production (as measured by the percent juveniles in the harvest) was 31 percent, lower than the 21 year average (1993-2013, 48 percent). The number of chicks per hen was 0.7. This represents a decrease from the 2013 production value of 2.0 chicks per hen and the long-term (1993-2014) average of 1.5. This is despite the fact that nest success improved in 2014, with an estimated apparent nest success of 51 percent. The low production and proportion of chicks in the harvest could be related to sub-optimal forage conditions resulting from on-going dry climatic conditions and presumable higher chick mortality. A similarly low chick per hen ratio occurred during a drought year in 2007 (0.6) and was followed by a 37 percent decline in the 2008 minimum spring population estimate. Thus, the 2014 low production is expected to result in a lower spring population in 2015.
Additional Resources
- Blomberg, E.J., D. Gibson, M.T. Atamian, and J.S. Sedinger. 2014. Individual and environmental effects on egg allocations of female Greater Sage-Grouse. Auk 131:507-523.
- Blomberg, E.J., J.S. Sedinger, M.T. Atamian, and D.V. Nonne. 2012. Characteristics of climate and landscape disturbance influence the dynamics of Greater Sage-Grouse populations. Ecosphere 3:55.
- Drut, M.S., W.H. Pyle, and J.A. Crawford. 1994. Diets and food selection of sage grouse chicks in Oregon. Journal of Range Management:90-93.
- Fischer, R.A., K.P. Reese, and J.W. Connelly. 1996. Influence of vegetal moisture content and nest fate on timing of female sage grouse migration. Condor:868-872.
- Johnson, D.H., M.J. Holloran, J.W. Connelly, S.E. Hanser, C.L. Amundson, and S.T. Knick. 2011. Influences of environmental and anthropogenic features on Greater Sage-Grouse populations, 1997-2007. In S.T. Knick and J.W. Connelly (eds.). Greater Sage-Grouse: ecology and conservation of a landscape species and its habitats. Studies in Avian Biology (Vol. 38), University of California Press, Berkeley, CA.
- Miller, R.F., P. Doescher, and T. Purrington. 1991. Dry-wet cycles and sagebrush in the Great Basin. Management in the Sagebrush. Steppe:8.