BEIJING, June 20 (Xinhuanet) -- Female and male Nazca booby chicks -- a Galapagos Island seabird -- are ready to fight to the death as soon as they hatch because of elevated levels of testosterone and other male hormones, according to a new study.

    "The older of two Nazca booby hatchlings unconditionally attacks and ejects the younger from the nest within days of hatching," said David J. Anderson, professor of biology at Wake Forest University.

    Because the parents of this species find it hard to raise more than one, by killing the younger sibling, the older chick stands a better chance of surviving.

    Surviving chicks also frequently seek out nestlings in their colony, and during those visits they often bite and push around the defenseless youngsters, the researchers found.

    Blood samples were taken from chicks within 24 hours of hatching. In 15 nests with two eggs, blood samples were taken from both hatchlings. Samples were also taken from 15 hatchlings in one-egg nests. Some Nazca booby nestlings experience a one-two hormonal punch, raising their aggression hormones even higher when they actually have a nest mate. The nestlings that fight siblings become bigger bullies as adults than the Nazca booby nestlings who never fight.

    "The hormones that are part of this epic battle early in life seem to permanently change some aspects of their social personality," Anderson said.

    Nazca booby chicks have aggression-related hormone levels three times as high as their less aggressive cousins, the blue-footed boobies. Blue-footed boobies do not have the same lethal fights right after hatching and do not go on to bully their fellow birds as adults.

    (Agencies)