Sounds Wild


Download Episode: Eggs (MP3 file 1,409 kB)



On a summer day on Round Island, a colony of murres is busy tending their eggs. Murres are seabirds related to puffins, and they spend most of their lives on the water. When it's mating season, they group up in large colonies, pair up, and lay eggs. The colonies are on cliffs, ideally cliffs inaccessible to land predators like foxes. Murres don't build nests, but lay their eggs on rock ledges. The eggs are not shaped like familiar chicken eggs; they're long and pointed at one end. The shape prevents them from rolling off the edge of the ledge. A rolled murre egg circles around on its pointed end.

Bird eggs come in a variety of shapes. Hummingbirds' eggs are elliptical, tiny symmetrical ovals just a half-inch long. Owl eggs are much rounder than most birds' eggs.

Some birds, like murres, lay just a single egg, while other birds like grouse and ptarmigan can lay more than a dozen eggs when they nest. The reason a chicken can lay an egg a day for months at a time is because they are what's called "indeterminate layers." They're trying to accumulate a clutch of eggs in the nest, ideally about a dozen to fifteen. If the eggs are taken every day, they just keep on laying. Other birds are "determinate layers," and will lay only a certain number of eggs no matter what. If an egg is broken, or taken, it's not replaced.