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COSEWIC assessment and update status report on the Sage Thrasher Oreoscoptes montanus in Canada

Limiting Factors and Threats

Because of the Sage Thrasher's dependence on the sagebrush environment, almost all of the factors limiting its populations concern the loss, alteration, or degradation of this environment.

Loss of sagebrush habitat to agriculture, strip mining and residential developments has caused great concern for birds dependent on that environment in the United States (Braun et al. 1976).  Huge areas of sagebrush in Washington state have been converted to wheatfields in the past century, especially since the construction of the Grand Coulee Dam (Weber 1980).  Sizeable areas of Alberta Sage Thrasher habitat have been lost to agricultural development of dryland farming areas (Bruce MacGillivray, pers. comm.).

Approximately half of the historic area of sagebrush steppe in the United States has been lost to intensive agriculture, and only half of the remaining portion is in good grazing condition with native understory remaining (West 1996).

There are few data concerning the effects of pesticides on Sage Thrashers.  Aerial application of Malathion (585 gm/ha) in Idaho reduced the insect population available to breeding thrashers, but there were no significant effects on nestling survival (Howe et al. 1996).