| Abstract/Description or Keywords |
Songbirds breeding in riparian habitat within valleys where hydroelectric power generation regulates water levels may suffer increased nest mortality or reduced survival if rising water levels flood active nests or reduce food availability. We have studied yellow warblers (Dendroica petechia) breeding in three types of riparian habitat adjacent to the Upper Arrow Reservoir near Revelstoke, BC since 2004. Previous work showed that variation in dam operations in 2005 and 2006 did not have a significant on the breeding success of yellow warblers. In this study we assessed whether differences in the timing of inundation and maximum water level at full pool in 2005 and 2006 influenced the return of breeding adults in the following year. We found that despite large differences in dam operations in the two years adult return rates in 2006 and 2007 did not differ. Return rates combine both a measure of survival and breeding dispersal but no birds were observed to move between the three study sites within Revelstoke Reach. This study therefore suggests that differences in dam operations in 2005 and 2006, (years with low and high water levels at maximum pool, respectively), did not have a significant impact on adult survival. Differences in how nestlings were banded in 2005 and 2006 made it impossible to evaluate whether dam operations influenced juvenile survival. However, our failure to detect any returning juveniles from the 2006 cohort warrant further work on the impact of dam operations on juvenile survival. We also found that the return rates of male and female yellow warblers did not differ significantly (overall rate of return was 44%). Return rates were however approximately three times higher at Machete Island, the site containing continuous willow habitat bordering mature cottonwoods, than either Drimmie Creek a site with fragmented willow habitat, or Illacillawaet, a restored riparian site. This supports previous work that concluded continuous willow habitat bordering mature cottonwoods constitutes high quality habitat for this riparian dependent songbird. |
