This Bird Takes Sibling Rivalry to Extremes

Sibling rivalry can be pretty intense among humans but it rarely rises to the level seen in seabirds called Nazca boobies, NPR reports in a look at two extremes of avian sibling relationships.

• Wake Forest University researcher David Anderson, who has studied Nazca boobies in the eastern Pacific for decades, says he often saw nests with one little chick and one big chick—and the smaller one always disappeared from the nest, often to be found dead nearby. He says the species isn't great at hatching eggs, so a second one is often laid as an insurance policy a few days after the first. But if both hatch, the larger chick will literally kick the smaller one out of the nest and its mother will not retrieve it. "It's common for sibling competition to happen in a nest of bird babies," Anderson tells NPR. "It is relatively rare for them to actually attack each other."

• At the other extreme, acorn woodpeckers, found in the western US, live in tight-knit family groups, with siblings often raising their offspring together. Ecologist Natasha Hagemeyer tells NPR that she observed one group of five sisters teaming up to fight off other birds that wanted to occupy newly available breeding areas. The fights, she says, "involve birds chasing each other, screaming, displaying and also grappling in midair, to the point where sometimes they will hit the ground and still be fighting." She says all five birds in the woodpecker sisterhood ended up with territories where they could start breeding.

(More birds stories.)