January 27, 2006
Egg Development
Nest Update: Fortunately our camera seemed to hold up pretty well during the big wind we had this week, and the two eggs look good in the nest. Some cam watchers have asked about what looks like cracks on the eggs. Sometimes pieces of grass fall on the eggs when the parents are moving around, and from our view they look like cracks, but they're not.
Also, one note about the Gallery. If anyone wondered why their photos didn't make it into the last update, my email provider was very slow in getting me the emails that were delayed last week when their server went down. I got some of the Gallery emails a week late, so they didn't get to me in time for the update. The problem seems to be fixed now, so please keep sending your photos. :-)
Now that we have a clutch of two eggs, it's natural to wonder about their care and development. When watching the cam, we sometimes see the parents leave the eggs alone. While it's true that the parents will sometimes step out of the nest for a break, it's not likely that the eggs are completely alone; a parent is probably in a nearby branch. Experienced parents know they shouldn't leave their eggs unattended if they want to keep them.
In our Gallery photos we also occasionally see the parents turning the eggs. This is done about once an hour to prevent the membranes and tissues from sticking to the shell wall. Often the parent will roll the egg with a balled-up talon so as not to puncture the eggshell.
When the parents sit back down on their brood, they place the eggs in contact with their brood patch (both female and male eagles have one, although the female's is larger). The brood patch is an area on the eagle's belly where the feathers have dropped out and naked skin is exposed. The skin area has a larger blood supply, so it's like a hot-water bottle resting against the eggs.
If the parents do a good job of keeping the eggs warm, then the cells inside the egg will begin to turn into vital organs, wings, a beak, a tail, etc. Much research has been done on how chickens grow inside their shells, and the results are useful in getting a glimpse into how the eaglets develop. This Embryonic Development Chart shows how a chick develops during the chicken's 21-day incubation period. The chicken's incubation period is about two weeks shorter than the eaglet's, but the general body parts are all there.
In a future log post we'll talk about what's inside the shell, such as the air sac (where the chick gets its first breath of air) and the yolk (which the chick uses for nourishment).
Sometimes eggs will not hatch, and there can be several reasons for this, such as the egg was infertile, the parents had a poor diet or were exposed to pesticides, the eggs were not turned often enough, the eggs were not kept warm enough, or the membranes and tissues inside did not develop properly.
When you consider all the miraculous things that must happen for a small collection of cells to turn into a baby bird, you can understand why many biologists consider the transformation of an egg into a chick as one of the great miracles of nature. And it's even more miraculous when you think about the journey that an eaglet will eventually take from a helpless chick to a powerful, soaring bird of prey. As of today, the eggs are 8 and 10 days old. Their journey is just beginning.
Until next time,
Lisa - webmaster
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