Corvid survey techniques and the relationship between corvid relative abundance and nest predation
2001
Luginbuhl, John M. | Marzluff, John M. | Bradley, Jeffrey E. | Raphael, Martin G. | Varland, Daniel E.
We conducted a four-year study on the Olympic Peninsula of Washington to assess the relationship between corvid (Gray Jay [Perisoreus canadensis], Steller's Jay [Cyanocitta stelleri], American Crow [Corvus brachyrhynchos] and Common Raven [Corvus corax]) abundance and the risk of nest predation. We assessed risk of predation through the use of artificial mid-canopy nests and assessed corvid abundance using a variety of techniques including point-count surveys, transect surveys, and the broadcast of corvid territorial and predator attraction calls. Point counts of corvid abundance had the strongest correlation with predation on artificial nests containing eggs. The relationship between nest predation rate and corvid abundance was strongest when study plots were used as replicated measures of landscape conditions rather than as independent samples. We suggest using the maximum value for each corvid species attained from several temporally replicated point-count surveys in each study plot. Corvid point-counts should be conducted on days with light winds (<20 kph) and no more than light precipitation. Use of attraction calls is important for gaining a meaningful measure of corvid abundance. Their use may overrepresent corvids at the local plot scale but is important in assessing the landscape scale presence of wide-ranging (American Crows) and often non-vocal (Gray Jays) corvids.
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