The best chance of observing eggs in North American bird nests occurs during the breeding season, which runs from approximately the middle of March until August.
Birds build nests in a variety of habitats, ranging from ground nests, as used by the common loon, to very tall trees, such as those of the great blue heron. Identification of eggs is made easier when you are familiar with the birds that may reside in a particular area. A nest in a backyard thicket containing cream-colored eggs speckled brown might be that of a northern cardinal, as this bird prefers the concealing tangle of brush and vines.
North American bird eggs come in many colors, markings, sizes, shapes and textures. Even the glossiness of shells varies among different birds' eggs. Egg color can act as camouflage from predators, such as the speckled eggs of the killdeer, which builds a ground nest. Also, as expected, smaller birds produce smaller eggs, and larger birds produce larger eggs. Narrowing down your possibilities for identification is enhanced with some basic knowledge of egg type.
Use a bird identification field guide that includes illustrations and descriptions of eggs and nests. Keep in mind that while the illustrations will provide a good idea of what a specific egg looks like, there can still be variations among the same species from region to region.
After determining the color and size of the egg, look closer to see if it is spotted, speckled, streaked or marbled. Some eggs have a heavy concentration of markings in a particular place--for example, the Carolina wren's eggs have brown speckles often found toward the base. Also , the number of eggs in a nest can be a clue to their identify.
Care should be taken when hiking near any body of water, as many North American waterfowl such as ducks and geese build ground nests along the banks of lakes and rivers.
Article Written By Paul Weidknecht
Paul Weidknecht’s non-fiction has appeared in "Outdoor Life," "Yale Anglers' Journal," "Fur-Fish-Game," "Snowy Egret," and elsewhere. His fiction has appeared in "Clapboard House," "Potomac Review" online, "Stone's Throw" magazine, "The Oklahoma Review," and "Freight Train" magazine. He lives in northwest New Jersey. He holds a Bachelor of Arts in psychology from Muhlenberg College.