February 14, 2006
The Hatching Process
Nest Update: It looks like the eagle family and our cam equipment made it through the snowstorm in good shape. Fortunately the total snow accumulation around the refuge was not as high as was originally predicted.
Several cam watchers wrote in to ask why the female eagle was holding out her wings while sitting on the nest during the storm. From what we could tell, it seemed the female was attempting to keep a larger area of the nest snow-free. And if you look at these two photos, you can see that it worked.
When the smaller male exchanged places with her on the nest and sat on the eggs with his wings tucked in, you could see how little an area he was covering compared to the female. The female -- with her larger body and bent wings -- managed to keep the center of the nest from accumulating too much snow.
Hatching Time
We're now getting close to the hatching dates. Based on a 35-day incubation period, we calculated that we should see hatching around Feb. 21 and 23. A sign that something is happening is if we see the female off the eggs and looking down at them. Chicks will move within the egg and call out as they're beginning to hatch, so the parents will know ahead of time that an eaglet is coming.
A while back I mentioned that we would talk about what is inside the eggs. If you looked inside a healthy chicken egg you'd see these components. The membranes help keep bacteria out, and the yolk holds the germinal disc with the female's genetic material. And at the blunt end of the egg you can see the small air sac.
When the chick is ready to hatch, it will pierce the air sac and start breathing air for the first time. Then it will use its egg tooth (on the tip of its beak) to chip away at the shell. The chick will frequently stop to rest -- since breaking free is very tiring and its lungs have to get used to fresh air -- then it will change position and continue cutting away until it has cut through the top end of the shell and is able to kick out the bottom section. This process could take 24 hours. Once the chick is out, it will not have to be fed right away because before it hatches, it absorbs the yolk and uses that for early nourishment.
The eggshells themselves are composed of calcium carbonate with thousands of tiny pores. The pores allow oxygen to enter the shell and also allow carbon dioxide and water to exit the shell. This is an important process because if too much carbon dioxide builds up inside the egg, the chick cannot survive.
Candling is a method frequently used to examine the contents of eggs before they hatch. If the eggshell is not heavily marked, a person can hold a light up to the egg and reveal the contents. On the Northern Prairie Wildlife Research Center website you can see photos of bird eggs that have been candled during the development of the chicks. The interesting thing to note when looking at the photos is how at the end of the incubation period, the chick is so large it almost fills the egg, except for the air sac at the top.
This year our camera is farther away from the nest, so our view of the hatching will be a little less detailed. The reason we moved the cam higher is so we would be able to see the eaglets when they are bigger and moving around the nest. But last year, we did have a super-close view of the hatching, so if you're new to our Eagle Cam, be sure to visit the 2005 Gallery to see the hatching photos. It will give you a good idea as to what we hope to see around the third week of February. If you look closely at the first few photos, you can see the first small hole that the chick has made to break out of the shell.
Until next time,
Lisa - webmaster
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