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Publication Date

Spring 2016


To better understand what is affecting bird populations, it is necessary to examine abundance of bird species in specific locations, and to make comparisons that may reveal possible ecological factors for observed trends. It may be helpful to compare population trends of Neotropical migrants and permanent residents, and species in different guilds. I examined a 23 year data set (1993 to 2015) from a constant effort mist-netting project conducted on the North Coast of California, using Monitoring Avian Productivity and Survivorship (MAPS) protocol. I analyzed capture rates per net hour as an index of abundance for 3 of the most commonly captured migratory song bird species and a common resident; namely, the Swainson’s Thrush, Wilson’s Warbler, Orange-crowned Warbler, and Song Sparrow. Using my index of abundance I found a decreasing trend in abundance for Swainson’s Thrush adults and hatch years (young known to have hatched in the calendar year), as well as for hatch year Song Sparrows. In addition, productivity remained steady throughout the study. Lastly, Swainson’s Thrush adult abundance in one year (t+1) was positively correlated with hatch year abundance the previous year (t). Wilson’s Warblers exhibited a negative correlation between adult abundance (t+1) and hatch year abundance (t). Analyses of data from the Wright Wildlife Refuge has not been published, spurring the need for my examination of passerine abundance and productivity in a relatively unchanged forest community.