Nature Bulletin No. 455-A   April 29, 1972
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

****:BIRD'S EGGS THEIR SIZE, SHAPE AND COLOR

There is usually a time, especially in his youth, when a man seems to 
have the instinct and habits of a pack rat or a crow. A boy is liable to 
collect anything from "lucky" pebbles or marbles to picture cards, 
stamps, cigar box lids or butterflies. There was a time, 50 years ago and 
more, when many boys and men, too -- collected birds' eggs. In search 
of nests they roamed the woods thickets, meadows and swamps.

Of course, we lads acquired a fund of nature lore. It took sharp eyes, 
patience and knowledge of their habits to discover a meadowlark's nest 
hidden beneath a clump of grass, or the tiny lichen-covered nest of a 
hummingbird. But many boys and men took every egg from a nest and 
those were sad days for the birds. There was brisk trading of eggs 
between collectors, not only locally but throughout the country, and this 
hobby was so popular that there were several magazines devoted to it. 
Fortunately, now and for many years there have been stringent federal 
and state laws forbidding such practices.

Bird's eggs are extremely variable in every respect. The elephant birds 
of Madagascar, now extinct, laid eggs about 14 inches long with a 
capacity of about 2 gallons. In contrast, a hummingbird's egg looks like 
a small bean. Domestic chickens, when pullets, often lay very small 
eggs at first and the last eggs laid by old hens are apt to be unusually 
small. There are eggs with shells so thin and fragile that they are almost 
transparent but the sculptured porcelain shell of an ostrich egg, about 6 
inches long, almost as much in diameter and weighing nearly 3 pounds, 
has to be opened with a hammer and chisel.

The eggs of birds vary in color from pure white to almost black. Those 
of the tinamous, South American game birds, have solid metallic colors 
and a finish like that of a new automobile. Most birds that nest in dark 
holes, like the kingfisher and the woodpeckers, lay plain white eggs; 
whereas those of the kill deer, whip-poor-will, plovers and terns, laid in 
exposed places with no protecting nest, are colored like the soil or 
gravel and are very difficult to find. The majority of birds that build 
protective nests lay eggs having a ground color of some delicate tint 
with spots, streaks or scrawls of darker pigment such as purple, brown 
or black and, often, this forms a kind of wreathe around the larger end. 
Robins and bluebirds have blue eggs but those of some other thrushes 
are spotted with darker color.

Birds' eggs are not even uniform in shape. Most of the 8600 or more 
species lay eggs shaped about like our familiar "hen fruit" but those of 
the owls and the Old World bee-eaters are nearly round, and many birds 
have eggs much longer than they are wide. The auk or murre nests on 
bare rock ledges of sea cliffs and lays an extremely pointed egg which, 
if accidentally kicked, will roll a circle instead of over the edge. Plovers 
and sandpipers also lay pointed eggs. Arranged on the ground, with the 
points inward, they occupy less space and, although rather large, can be 
more easily covered by the brooding mother.

Some of the penguins, albatrosses and other sea birds that nest in 
accessible places lay only one egg. The California Condor, nearly 
extinct, lay but one and that was true of the extinct passenger pigeon 
and the great auk. Wild ducks and game birds such as quail and 
pheasants, which have numerous enemies, lay 15 or more in a clutch. 
Most songbirds lay from 3 to 5, although hole-nesters like chickadees 
may lay 8 or more; tropical species seem to lay fewer eggs than their 
northern relatives; hawks and owls lay more eggs when their prey is 
plentiful; but nobody ever saw a square one.