Oology! It's a very special day!

 Today is Easter Sunday, Passover, Palm Sunday for Orthodox Christians, and April Fool’s Day—a rare confluence of events.  It is also the day after a blue moon, which is a second full moon in a month such as occurred in March 2018—on March 1^st and 31^st.  Our next full moon is April 29.  Thinking about the roundness of the glowing moon draws me to the subject of this post—eggs or the study of eggs--oology.

Eggs, dyed colorful eggs, are a part of the tradition of Easter and many other religions at spring time.  Eggs symbolize life, fertility, spring, and the future.  They are a tiny piece of hope.  In the Christian religion, they are meant to symbolize Jesus emerging from the tomb and being resurrected—in a sense breaking through the seal of the shell and coming back to life.

Drawing eggs, like the 90 plus eggs I drew for The Field Guide to the Neighborhood Birds of New York City, was a lesson in close observation of something that we may think of as simple or not think of at all but which in fact contains a mystery.  People dye eggs for holidays, but wild birds do it by themselves. For despite what we think, wild bird eggs are not all white, not all ovoid, and not all the same size as you can see in my drawing.  Wild bird eggs range in color from the white or brown we know from the supermarket and the turquoise we know from robin’s eggs to a rainbow of greens, reds, oranges, blues, tans, beiges, and even black.  It is also interesting that eggs that look white to the human eye may have bolder colors under ultraviolet light, which helps birds identify their eggs.  Birds’ eyes are tetrachromatic—they have four photoreceptor cells so they see not only the colors we do but also in the ultraviolet range, which we do not.   Calcium carbonate produces the white color of the shells while biliverdin produces the blue and green colors and protoporphyrin produces the yellow, red, brown and orangey colors. The two pigments together can make purples and exotic greens. 

Eggs come in lots of shapes.  Oval-shaped eggs are the most common, but many owls lay completely round eggs.  Shorebirds lay pointed pear-shaped eggs perhaps preventing them from rolling away thereby keeping them in place in the nest.  Some of the colors along with squiggles, specks, splotches, and streaks may help to camouflage the eggs so that predators do not steal them.  Wild bird eggs are very attractive to squirrels, rats, reptiles, and snakes as well as to other birds and for good reason.  Eggs are rich in good nutrients as many of us already know. Bird eggs are amniotic, which means they have a hard shell with a porous membrane for the exchange of oxygen and carbon dioxide.  The yolk is the part with the fat and protein that nourishes the growing chick. The shell is rich in calcium and parent birds will often eat the empty shells from their own chicks to both replenish the calcium in their body and to protect the nest from predators who might spy the shells. 

Bird eggs range in size from the hummingbirds with the tiniest eggs to the ostriches with the largest eggs. There was a time when humans collected wild bird eggs for their beauty and value, but it is not legal to do so anymore, so we have to admire them in museums and books. In fact, we need to discourage the removal of eggs from nests no matter how beautiful they are.  Many formerly common bird species are at risk from predators, even our beloved cats, and from environmental change.  The best thing we can do for the birds we love is to look, wonder, and ooh and aah about the mysteries contained in the shell, the nest, and the birds that hatch.