The delightful fragrance of sizzling bacon fills the kitchen as freshly cracked eggs plop into the frying pan. Along with whole wheat toast topped with English marmalade, few breakfasts are more delicious than eggs fresh from the backyard coop.
Before those eggs enter the pan, they’ve undergone a remarkable journey that starts in the hen’s ovary.
When a female chicken hatches she has two ovaries but one gradually shrinks and becomes unfunctional. The other gradually matures to generate all the eggs she’ll lay. When she’s about 20 weeks old, give or take a few weeks, a hen begins ovulation. It is the start of an egg’s formation and journey to the frying pan.
Good healthy layers ovulate every 24 to 26 hours. Then it takes about 26 hours before a complete egg enters the nest. After leaving the ovary the forming egg enters a part of the oviduct called the infundibulum…..a big word that means funnel. If a rooster is present fertilization takes place there. Lacking a rooster, the egg continues on its journey but will never be fertile. After about a half hour the egg moves into the magnum where the albumin, or egg white, forms. Three or four hours later it moves to the isthmus, where the inner and outer shell membranes form and the albumin completes development. Then it’s on to the uterus where the hard shell forms and a bloom is added. Finally, it moves to the hen’s vagina and exits her body through the cloaca, or vent. It leaves her body and enters the nest big end first.
That is quite a journey. Because it usually takes a little more than 24 hours to form an egg, even the most prolific layers skip a day every once in a while.
Eggs are one of the most nutritious human foods, but the protein and minerals people gain from eating them comes at a cost to hens. An extra-large egg weighs about 2.3 ounces. If she lays six eggs a week that’s almost 14 ounces of egg. That is nearly a pound, or about a fifth of her body weight. To keep laying and remain healthy hens must have nutrient and energy packed feed.
That chickens lay 200 to 300 eggs in a year is unusual in the bird world. Most bird species lay few eggs. Chickadees, wrens, cardinals, and robins nesting in suburban yards follow a common laying pattern. They make a nest in spring, lay a clutch of three or four eggs, and raise their babies. Sometimes they’ll raise two clutches a summer, so a female lays only a handful of eggs a year.
Pheasants, quail, and wild turkeys are closely related to chickens but still only lay a couple of dozen eggs a year during a limited mating season. Chickens evolved in the warm tropics and never had to deal with frigid winters. That may be why they don’t have a strong mating season and can lay throughout the year. For example, feral chickens in balmy Hawaii nest and raise chicks year-round.
Chickens have one other trait that helps them lay more eggs. Baby chicks, like those of pheasants, turkeys, and quail are considered precocial by ornithologists. This means the babies can walk, explore, and feed themselves soon after hatching. In contrast, most small birds have altricial babies born blind, relatively undeveloped, and unable to walk or find food on their own. Their parents must give them extended care that includes finding their food.
Parents of altricial babies must be workaholics and devote so much care to their babies they aren’t able to lay many eggs. Chicken parents have it easier and only need to show their babies where food is, keep them warm, and protect them from danger. They don’t need to gather food for their chicks.
If chickens were only able to lay a few dozen eggs a year, enjoying a savory breakfast of bacon, toast and eggs would be expensive and unusual. People are fortunate that hens lay almost every day. Every egg is the result of an epic journey through her body.