May 25, 2016
Not all ducks are created equal.
In female Wood Ducks, variation in individual quality is what matters for
breeding success and survival, according to the results of a new long-term study
being published in The Auk: Ornithological Advances.
Drawing on 11 years of data on
almost 500 ducks, Robert Kennamer of the University of Georgia's Savannah River
Ecology Laboratory and Gary Hepp and Bradley Alexander of Auburn University
found a positive relationship between annual survival and nesting
success—females that were better at raising their offspring were also better at
surviving. This contradicts an established theory predicting the existence of a
tradeoff between current reproductive effort and future success.
"Theory predicts that
current reproductive effort will negatively affect survival and future
reproduction," says Hepp. "In our long-term study of Wood Ducks,
however, females that nested successfully were not less likely to survive and
nest successfully again the following year compared to females that had nested
unsuccessfully." This suggests that there's a high degree of variation
between individuals, with healthier, higher-quality females living longer and
producing more offspring.
The study was carried out at the
Department of Energy's Savannah River Site in South Carolina. "Federal
legislation promoting the conservation and protection of the environment
provided the initial funding for Wood Duck population monitoring beginning in
1981 in an area of the SRS potentially impacted by thermal water releases from
the restart of a nuclear production reactor," according to Kennamer.
"When that resulted in a wealth of interesting data, we secured support
for continuing the project much longer than first anticipated."
The researchers suggest that
future studies should examine the factors that influence individual variation
in migratory birds and explore their impacts on the successful management of
these species. Birth and death rates and what causes them to vary are key to
increasing population sizes, guiding the decisions of wildlife managers and
conservationists, and this study highlights how much we still have left to
learn about how they work.
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