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Abstract

Sagebrush ecosystems across western North America have declined in productivity and biodiversity with significant declines in sagebrush obligate birds. Mechanical methods to reduce sagebrush canopy cover and encourage herbaceous undergrowth have been implemented to restore sagebrush ecosystems. How these treatments affect sagebrush obligate birds has not been documented. In this study, we hypothesized that nesting success would decline in mechanically treated (mowed and dixie harrowed) plots immediately and for two years after treatment. Twelve 6-ha plots within the South Parlin Common Allotment in the Gunnison Basin, Colorado were established in 2005. Four replicates of untreated (control), mowed and disked (dixie harrow) plots were sampled in 2005 (pre-treatment) and in 2006 and 2007. We located nests using the systematic walk and incidental flush method. We revisited nests every three to five days to determine nest fate. We located 142 nests of nine species in 90 nest searches and expended over 600 man hours. Mayfield nest success (proportion of nests that successfully hatch at least one young) and clutch size were similar among treatments. Nest success of artificial nests also was similar among treatments. Predation was the leading cause of nest failure accounting for 71 to 77 percent of all nest failures and small mammals were implicated in 76 percent of the depredations. Least chipmunks may have been the principle predator of sagebrush bird nests in our study. Small scale mechanical treatments to restore sagebrush apparently do not negatively affect sagebrush birds within two years post-treatment, but longer duration studies and larger sample sizes are required to better assess the impact of treatments on sagebrush avifauna.

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