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Songbird Population Trends Have Their Ups and Downs

Photo of Following a sharp decline in abundance related to West Nile Virus, western scrub-jays in California are showing recovery. Gary Woods. Following a sharp decline in abundance related to West Nile Virus, western scrub-jays in California are showing recovery. Gary Woods. Snapshot : Population trends and information on whether species are increasing or decreasing are crucial to managing and conserving species. Using 27 years of bird census data, Forest Service researchers found that abundance was quite variable. Even healthy populations have their good years and bad years, but remain stable in the long term. Of those species that showed significant changes, more species increased than decreased. A few species bear watching, including western scrub jays, which decreased following the appearance of West Nile Virus in California.

Principal Investigators(s) :
Purcell, Kathryn L. 
Research Location : San Joaquin Experimental Range, Madera County, Calif.
Research Station : Pacific Southwest Research Station (PSW)
Year : 2016
Highlight ID : 1117

Summary

Forest Service researchers examined population trends for 35 oak woodland bird species using 27 years of data on bird abundance collected at the San Joaquin Experimental Range in the Sierra foothills of California. Abundance of most species varied greatly during the study period, showing that species can persist despite having good and bad years. Overall, 12 species increased at the experimental range and five species decreased. For the species that increased, this is good news, except for the increase of the invasive European starling (Sturnus vulgaris). The five species that decreased included western scrub-jay (Aphelocoma californica), Blue-gray gnatcatcher, western bluebird (Sialia Mexicana), western meadowlark (Sturnella neglecta) and Bullock's oriole (Icterus bullockii). Of these, blue-gray gnatcatcher, western meadowlark and Bullock's oriole present cause for concern, and our results suggest the need for further research into the causes of their declines. Beginning in 2003, western scrub-jays showed a sharp decline that was likely related to West Nile Virus, but population levels began to recover in 2008 as birds with genetic resistance to the disease survived and became dominant.

Forest Service Partners

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  • Point Blue

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