The Mad Birds of Nazca – a seabird living on the Galapagos Island – appeared ready to kill his siblings in their first massacre. Biologists at the University of Wake Forest and their colleagues have found the link between this murderous behavior and high testosterone levels as well as the ratio of other male hormones in newly hatched birds.
The research will be published online in the June 18 issue of PLoS ONE.
According to Wake Forest biology professor David J. Anderson and head of the project, a high proportion of male hormones (also called androgens) increases aggression in young birds, whether male or female, making them available. Ready to fight to the death as soon as they hatch.
Much of the fieldwork was done by Martina Müller when she was a graduate student at Wake Forest University.
“The two mad birds of Nazca hatched before their unconditional decisive battle and then dumped the newborn just days after birth,” Anderson said. Since the madmen of Nazca have to raise more than one child, it will be very difficult, so the bigger chicks have to defeat the smaller one to increase their chances of survival.
High hormone levels also cause young birds that survive a fight to engage in bullying behaviors as adults, the study found. They often search flocks for young birds, then bite and intimidate those who cannot defend themselves during their visit.
Scientists took blood samples from young Mad Nazca birds within 24 hours of the outbreak. Of the 15 nests containing 2 eggs, the two young birds were collected blood. They also took blood samples from 15 young birds belonging to nests with a single egg. Next, researchers at the University of Maryland performed a hormonal test in the blood. For comparison, they did the same with the mad bird with blue feet – a close relative of the mad bird Nazca.
Researchers suspect that young Mad Nazca birds have elevated levels of aggression hormones during sensitive stages of their development, when their time-consuming growth patterns are susceptible to damage.
Some young Nazca birds have an even higher percentage of hormones associated with an aggressive nature when they have siblings. Those who have to fight with their siblings will become more ferocious bullies as adults than the Mad Birds of Nazca who never had to fight when they hatched.
“The hormonal involvement and the early battles seem to have changed some of their social characteristics,” Anderson said.
Young mad birds of Nazca have three times more hormones associated with an aggressive nature than their less aggressive siblings – mad birds with blue feet. Blue-legged boobies do not have life and death battles after hatching, nor do they become mature bullies.
