Bird eggs are one of nature’s many masterpieces both in appearance and function. They come in a wide variety of shapes and sizes. Shape-wise, it’s easy to stereotype eggs as all looking like chicken eggs. But hummingbirds, for example, lay eggs the shape of Tic-Tacs. Many owls lay eggs that look like golf balls. And other birds lay eggs at are pear-shaped. Scientists are still unraveling the mystery behind why different birds have different shaped eggs. The latest research suggests that birds that spend more time flying have more elongated eggs, while those that don’t lay rounder eggs. There are, of course, exceptions to this because king penguins lay eggs that are somewhat pear-shaped, but they don’t fly at all. They’re still researching.
The largest eggs are laid by ostriches – they are about 6 inches long and can weigh up to four pounds! It is no surprise that the smallest eggs are laid by hummingbirds; these eggs only weigh as much as a paperclip and are roughly a half inch long (but there are also many species of hummingbirds, some larger than others, so egg size also varies). Egg shells also vary in thickness. The award for the thickest egg goes to the cassowary of New Guinea and Australia, which are about ¼ inch thick!
Eggs also have different colors and patterns. The red-winged tinamou of South America, for example, lays monochromatic glossy eggs that vary from purple to yellowish green. Robins lay beautiful blue eggs. Other eggs have spots or speckles or streaks or lines like an abstract work of art, like that of the great bowerbird. In some cases, these markings work as camouflage to deter predators. Shore birds, for example, lay speckled eggs that blend in with pebbles or sand.
All bird eggs are made of calcium carbonate. Interestingly, but not surprisingly, this is the same material mollusks build their shells from! Bird eggs are also porous. This leads to a question that had never occurred to me until investigating eggs: how does a developing chick breathe? As it turns out, there is a small pocket of air in the egg. The chicks breathe this air and exhale carbon dioxide, which can then escape from those pores! The pores also allow moisture in. This protects the baby bird and the inside of the egg from drying out. If you think about it, eggs are kind of brilliant. They offer the developing chick shelter, food, air, moisture – everything it needs!