Bluebird moms inadvertently fuel wars between species
Extra hormones delivered to sons in tough times have far-reaching consequences
![Male bluebird feeds female](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2015/02/sm_male_feed_female.jpg?fit=860%2C460&ssl=1)
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