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Bluebirds & Fire

February 23, 2015

Bluebird mothers control their sons’ ability to compete for habitat in post-fire habitat.




A female western bluebird outside a nest cavity. (© Alex Badyaev)

Female birds and forest fires. I’m Bob Hirshon and this is Science Update.

After forest fires, bluebirds in the western U.S. compete over scarce nest cavities inside dead trees. Mountain bluebirds settle in first, followed by western bluebirds. Now, University of Arizona biologist Renée Duckworth reports in the journal Science that female western bluebirds become aggressive as their own nest sites become crowded. Levels of hormones like testosterone increase, and are deposited in their eggs. This results in more competitive sons.

RENÉE DUCKWORTH (University of Arizona):

Females from crowded populations are more likely to produce aggressive sons that leave and colonize new populations.


Their aggressive offspring are better able to take over the mountain bluebird nest sites. Duckworth and her team report that these maternal effects probably give the birds an evolutionary advantage in the face of competition. I’m Bob Hirshon, for AAAS, the science society.