The Museum opened its doors this May 1st with 501 birds! An incredible milestone, but of course Bob and the staff have plans for still more. But have we ever mentioned—in addition to the birds—how many carved eggs there are? So many of our bird displays are complete with parents, nest, habitat, and eggs, that it seems worth some mention. After all, which came first?
Often the closest we come to seeing bird eggs in the wild is finding an empty cracked shell lying along a woodland path or suburban lawn—cast off remains, once vital to a developing bird’s survival—and that’s eggsactly as it should be (legally). As animals moved onto shores and adapted to a terrestrial life, egg evolution favored a strong, protective covering to house and nurture the fertilized ovum through gestation—strong enough to remain when the chick has emerged.
Bird eggs are comprised of a calcium-rich, porous shell that surrounds several membranes that cushion, “ventilate,” or remove wastes from the embryo. The yolk supplies nutritional proteins and fats to the embryo. Tiny pores in the shell allow for gas exchange. A surface cuticle, whose texture can be described variously as smooth, glossy, chalky, or soapy, gives the shell strength and helps shield the egg against bacteria.
Just as there are myriad bird species and habitats, the sizes, shapes, and colors of eggs are remarkable and evolutionarily significant. In general, the bigger the bird, the bigger its egg. Hummingbirds lay the smallest eggs while Ostriches produce the largest eggs. Michael Walters, in Birds’ Eggs, describes eight different egg shapes: cylindrical, conical, pyriform (pear-shaped), biconical, oval, elliptical, spherical, and longitudinal. Shape is often critical to avoiding egg breakage at a nesting site. Many seabirds, who lay their egg clutches on steep seaside ledges, characteristically produce pyriform eggs that tend to roll around in circles rather than rolling off. Interestingly, conical eggs can be arranged in the nest with the pointed ends together affording all the eggs an even distribution of warmth from the brooding parent. The eggs of cavity nesters are typically spherical in shape, hummingbirds produce cylindrical eggs, and grebes tend toward a biconical shape.
It’s an eggciting and marvelous journey ahead for a newly formed egg cell. As each ovum travels along the mother bird’s oviduct, it is coated with albumen (the protective “egg white”) before reaching the isthmus where shell membranes are added. As the egg enters the uterus, a pigment wash covers it before delivery through the cloaca.
Spotting and streaking of color onto the shell occurs due to the egg’s movement during pigmentation. Essentially, only two pigments are involved with egg coloration, both of which are associated with the red blood pigment, hemoglobin. Bile is the source of bluish-green and white colors. Pigments appearing yellow to red or brown and black make up the other basic color; a combination of red and blue pigments results in an even wider range of hues. Birds such as owls and kingfishers lay white eggs, perhaps to make their eggs are more easily seen in dark tree cavities or tunnels. Birds that depend on camouflaging coloration for their eggs are typically ground nesters, such as wading and shore birds.
The Museum is hatching up a few plans for egg-related educational displays and activities this celebration season. Please get crackin’ and come on by! You can try to find all 535 unhatched eggs on display. (And discover which bird’s eggs have hatched!)