The Amazing Egg!

 

March 25, 2010 by Bob Sallinger

The eggs are now 22, 19 and 16 days old respectively and it seems appropriate to spend a few minutes considering the amazing egg. The egg is basically a vehicle to nourish and protect the embryo until it is developed enough to survive in the environment.  Some birds like red-tailed hawks are atrical meaning that even after they hatch, they are still relatively helpless and are completely dependent on their parents for survival. Other bird species such as killdeer and Canada geese are precocial meaning that they emerge from the egg in a fairly advanced state of development and are able to walk and self feed almost as soon as they emerge. Precocial birds usually leave the nest and follow their parents around on the day that they emerge while atrical birds spend additional time --for red-tails usually about six weeks--in the nest continuing to develop.

The main structures of the egg are the yolk, albumen (egg white) and shell. The yolk is a food source for the growing embryo. It is loaded with fat gobules and protein. The albumen (or egg white) is a viscous fluid that surrounds the embryo and the yolk and serves as a shock absorber for the embryo which sits on top of the yolk. The shell is comprised of three layers and serves to protect for the egg. It is porous and allows for gas exchange with the outside environment. Several local species including peregrines, osprey and bald eagles were almost lost because the pesticide DDT which was used during the 1940, 50s and 60's blocked an enzyme in birds necessary to create calcium and these species laid eggs with thin eggshells which cracked during incubation. The embryo which will eventually become a bird, begins as only a millimeters in length but grows rapidly. By ten days it is already beginning to look like a bird in shape.

 The size, shape, number and color of eggs varies greatly among different species. A hummingbird egg weighs 0.3 grams while an ostrich egg can weigh as much as 1600 grams. Coloration patterns often serve as camouflage to hide the eggs from predators. I could go on...but I will save that for another day and simply leave you with some final words from Clarence Day on the amazing egg.

Oh who that ever lived and loved
Can look upon an egg unmoved?
The egg it is the source of all.
'Tis everyone's ancestral hall.
The bravest chief that ever fought,
The lowest thief that e'er was caught,
The harlot's lip, the maiden's leg,
They each and all came from an egg.

The rocks that once by ocean's surge
Beheld the first of eggs emerge—
Obscure, defenseless, small and cold—
They little knew what eggs could hold.
The gifts the reverent Magi gave,
Pandora's box, Aladdin's cave,
Wars, loves and the kingdoms, heaven and hell
All lay within that tiny shell.

Oh, join me gentlemen, I beg,
In honoring our friend, the egg. 

Clarence Day