Background: Biodiversity offsets provide a mechanism to compensate for unavoidable damages from new energy development as the U. S. increases its domestic production. Proponents argue that offsets provide a partial solution for funding conservation while opponents contend the practice is flawed because offsets are negotiated without the science necessary to backup resulting decisions. Missing in negotiations is a biologically-based currency for estimating sufficiency of offsets and a framework for applying proceeds to maximize conservation benefits. Methodology/Principal Findings: Here we quantify a common currency for offsets for greater sage-grouse (Centrocercus urophasianus) by estimating number of impacted birds at 4 levels of development commonly permitted. Impacts were indiscernible at 1-12 wells per 32.2 km(2). Above this threshold lek losses were 2-5 times greater inside than outside of development and bird abundance at remaining leks declined by -32 to -77%. Findings reiterated the importance of time-lags as evidenced by greater impacts 4 years after initial development. Clustering well locations enabled a few small leks to remain active inside of developments. Conclusions/Significance: Documented impacts relative to development intensity can be used to forecast biological tradeoffs of newly proposed or ongoing developments, and when drilling is approved, anticipated bird declines form the biological currency for negotiating offsets. Monetary costs for offsets will be determined by true conservation cost to mitigate risks such as sagebrush tillage to other populations of equal or greater number. If this information is blended with landscape level conservation planning, the mitigation hierarchy can be improved by steering planned developments away from conservation priorities, ensuring compensatory mitigation projects deliver a higher return for conservation that equate to an equal number of birds in the highest priority areas, provide on-site mitigation recommendations, and provide a biologically based cost for mitigating unavoidable impacts.
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