Estimating wood thrush (hylocichla mustelina) annual reproductive success over a 34-year period (1974-2008)

Date
2010-05
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University of Delaware
Abstract
Apparent nest survival is commonly calculated to report avian reproductive success, however other metrics such as annual reproductive success (ARS) have been proposed in its place. I calculated apparent nest survival and measures of ARS to determine their value to avian reproductive studies using Wood Thrush (Hylocichla mustelina) reproductive data collected at the University of Delaware Ecology Woods (UDW) over a 34-year period (1974-2008). I also examined the affect of Brown-headed Cowbird (Molothrus ater) brood parasitism on the reproductive success of this Wood Thrush population over the same time period. I compared apparent nest survival to two measures of annual reproductive success: the annual number of successful broods per female and the annual number of fledglings produced per female. Apparent nest survival was able to predict successful broods per female and fledglings produced per female, which indicated that apparent nest survival approximates measures of ARS. Because apparent nest survival can approximate ARS, calculating ARS is not necessary for all avian reproductive studies. Because successful broods per female and fledglings produced per female require an individually marked population to be calculated, attempting such calculations would not be practical if marking each individual is unrealistic or simply not necessary. ARS should however be estimated for existing long-term avian reproductive studies because doing so can provide demographic data and further insight into the factors limiting populations. Linear regression analysis revealed that measures of cowbird success (percent nests parasitized and number of cowbird eggs laid per nest) were able to predict Wood Thrush production. If cowbird parasitism is causing reduced Wood Thrush reproductive success, parasitism may be aggravating declines in this species. Future studies should quantify the effect of parasitism on Wood Thrush production and investigate the ability of parasitism to cause complete nest failure in Wood Thrush at the UDW.
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