Juvenile and Adult Survival of Swainson's Thrush (Catharus Ustulatus) in Coastal California: Annual Estimates Using Capture-Recapture Analyses
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[edit] Author(s)
- Gardali, T.
- Barton, D. C.
- White, J. D.
- Geupel, G. R.
[edit] Journal
Auk 120.4 (2003): 1188-94.
[edit] Keywords
marked animals population productivity demography dispersal rainfall dynamics forest vireos models
[edit] Abstract
We estimated annual rates of survival for juvenile and adult Swainson's Thrushes (Catharus ustulatus) using capture-recapture analyses from 22 years of mist-netting data in coastal California (n = 2,651 individual captures). Our apparent survival estimate was 56% for adults and 25% for juveniles. We are the first to estimate an annual juvenile survival rate for a Neotropical migrant using capture-recapture probability estimates. Like most estimates of annual survival, we could not distinguish between dispersal away from our study area (which is likely high for juveniles) and mortality. Hence, survival is underestimated. However, our juvenile survival estimate did not include the period from fledging to independence, a time when mortality can be high. Many researchers have assumed juvenile survival to be half that of adult survival in population models (e.g. source-sink). Our juvenile to adult survival ratio was 45% (95% CI = 27 to 65%). We caution researchers from simply assuming that juvenile survival approximates half of adult survival when modeling populations and suggest using a range of values. Using a range of values is prudent because of the potential for annual variation, site-specific variation, and especially because estimates are imprecise or completely lacking. Received 10 April 2003, accepted 6 June 2003.
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