VDGIF/Norfolk Botanical Garden Eagle Cam

The Virginia Department of Game and Inland Fisheries, in partnership with the Norfolk Botanical Garden and WVEC, is providing a rare glimpse into the life of two bald eagles and their offspring!

Tuesday, March 02, 2010

“Inside The Eggs”

The embryos inside the eggs continue the final stages of development. At this point many recognizable structures are in place and the major organ systems are largely formed. There are no highly detailed studies of the embryology of bald eagle eggs - but we can use studies from other raptors, namely American kestrels (Falco sparverius) as a rough guide to what might be happening inside the egg.

By now the feathers of the natal down are in place. The bill has started to harden and scales are covering most of the legs and toes. The eyes are closed and the complexus muscle (hatching muscle) has begun to swell. Much of the remaining amniotic fluid inside the chorioallantois membrane (see archive for egg diagram) has been absorbed. We’ll post again in the coming days with more of what’s happening inside the eggs as they get closer to hatching.

This information is based on:
Pisenti JM, Santolo GM, Yamamoto JT, Morzenti AA. 2001. Embryonic Development of the American Kestrel (Falco sparverius) External Criteria for Staging. J Raptor Res. 35(3):194-206

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Thursday, February 18, 2010

“When Will They Hatch?”

Now that the eagles are settled in and incubating their three eggs - the big question is when will the eggs hatch? In addition to our knowledge about bald eagle biology, we have this pair's previous history to help guide us.

The scientific literature generally reports an incubation period of 35 days (although various authorities may list 34-38 days). Directly observing when bald eagles lay eggs and when they hatch has always been a challenge for biologists, sometimes limiting how precisely we could record events. The advent of technology such as the Eagle Cam has allowed both researchers and the public an unprecedented view of what actually happens in the nest.

We can now document when eggs have been laid and when they hatch with great accuracy (often to the minute). This will help us to better understand the nesting ecology of these birds. A table of the egg laying and hatch dates since the camera has been active is included below.

Given past history - the average time for this pairs first egg to hatch has been just over 38 days (38days 3.6 hours). This would put our first egg hatching on March 9th. The second egg has hatched after an average of 37 days 7 hours and the third has averaged 36 days 3 hours. There is a clear trend of reduced incubation times for later eggs. By ensuring that the eggs hatch closer together, the disadvantage of the youngest chick is minimized. The eagles accomplish this by delaying full time incubation of the first egg (and to a lesser degree the second). This slows development and helps reduce the difference in hatch dates. It will be interesting to see if the trend holds true this year. As the first egg was laid in a snowstorm -the adults had to begin incubating it immediately. Whether or not this will have any effect in hatch dates remains to be seen.

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