News Ecosystems

Bluebird moms inadvertently fuel wars between species

Extra hormones delivered to sons in tough times have far-reaching consequences

Male bluebird feeds female

BREEDING AGGRESSION   Among western bluebirds, harassed mothers tend to give extra hormones to their eggs, a gift that ends up leading to waves of hostile takeovers.

Alex Badyaev

By Susan Milius

- More than 2 years ago

Bluebird wars begin with the power of vexed moms in their nests.

Experiments show that female western bluebirds (Sialia mexicana) harassed by other species competing for nesting cavities tend to lay eggs with abundant testosterone, says evolutionary ecologist Renée Duckworth of the University of Arizona in Tucson.