The Nazca booby, a Galápagos Island seabird, emerges from its shell ready to kill its brother or sister. Wake Forest University biologists and their colleagues have linked the murderous behavior to high levels of testosterone and other male hormones found in the hatchlings.

Being a devoted husband and father is not enough to keep an avian marriage together for the Nazca booby, a long-lived seabird found in the Galapagos Islands off the coast of Ecuador.