Back to Nature (Published on - March 29, 2007)
Avian reproduction
Illustration by Karen Mitchell Tremmel
Birds eggs come in many sizes and beautiful colors.
Grand Slam special: Two eggs, pancakes and sausage. Did you know that per capita the average American eats close to 255 eggs a year?

Besides the all American breakfast, consumers get their daily dose of eggs in cakes, pasta, cereal and even some candy bars.

Currently Florida ranks No. 8 out of the top 10 egg producing states. According to U.S. Department of Agriculture, American Egg Board, USAPEEC:

• U.S. egg production during June 2006 was 6.56 billion table eggs. Total U.S. egg production during 2005 was 76.98 billion table eggs.

• In 2005: Per capita consumption reached 255.1. Per capita consumption is a measure of total egg production divided by the total population. It does not represent demand (USDA has recently adjusted data to reflect 2000 Census figures.)

So where do eggs come from? Birds lay eggs. Well of course, we know that birds lay eggs, but how does an egg become an egg and how does an egg become a chicken. If you are laughing about now while asking yourself that age old teaser, “Which comes first, the egg or the chicken?” for the sake of argument, let’s assume there exists two birds, one male and one female. In many ways this process is not that different from human beings.

Fertilization in any animal depends on production of eggs from the female and sperm from the male. The female mammal produces an egg. That egg must be fertilized by the sperm from a male to produce offspring. For most birds, copulation involves a “cloacal kiss,” with the male on the female’s back and twisting his tail under the female’s – copulation typically lasts just a few seconds.

Dennis Chang, graduate student and HHMI predoctoral fellow at Harvard University, has this to say about that:

“Birds, like mammals, use internal fertilization. Many species of birds lack a penis; instead, the males just has a genital opening (cloaca), which must be positioned against the female’s genital opening (also called a cloaca) for sperm transfer. Male chickens, however, do have a small penis to facilitate mating. In any case, after copulation, which only lasts a few seconds, the sperm quickly swim up the oviduct toward the ovary. The sperm can stay alive in the oviduct for several weeks, ready to fertilize the next egg cell (oocyte) that appears.

“After a yolk package is released it lingers there for about 20 minutes. If sperm are present, then the egg cell is fertilized and becomes an embryo. But if no sperm are around (that is, if the hen has not mated), then the egg still proceeds down the assembly line of the oviduct. In this assembly line, albumen (egg white) is added around the yolk, shell membranes are added, and the shell itself is constructed.

“Finally, the complete egg is pushed through the vagina and out the cloaca. If the egg has been fertilized, then the embryo inside has already divided several times but remains a group of unspecialized cells. When the egg is incubated at about 37 to 38 degrees C, the embryonic cells differentiate to form a chick, which will hatch after 21 days.”

“The hen’s reproductive system can be divided into two major components: the ovary and the oviduct. The ovary produces the egg yolk. The oviduct adds the white, shell membranes, and shell to the yolk to complete egg formation.” Information Sheet 16º10, by Dr. Chris McDaniel, associate professor, Poultry Science Department, Mississippi State University.

Female birds do not need a male to lay eggs. Unfertilized eggs are laid regardless of whether there is a male present in the hen house. Although having grown up raising chickens, those hens would stop laying if the rooster didn’t crow, so to speak. Every year or so it was necessary to purchase a new rooster to bring in new blood, as well, to bring back a little romance for the pining hens. Most eggs that reach the supermarket shelves are not fertilized.

Eggs come in all sorts of sizes, shapes and beautiful colors. If you’re traveling on spring break or this summer why not take a tour at one of these great museums to observe birds up close, as well, bird egg collections: The Royal Ontario Museum’s Gallery of Birds, Norfolk Museum, The Richter Museum of Natural History, Finnish Museum of Natural History, Harvard Museum of Natural History.

There are always so many beautiful things to see and learn … back to nature.

Karen can be reached at

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