2/19/17 – Hays eagles re-nesting after loss

2/19/17 – It was one week ago when the Hays Bald Eagles lost their nest, nest tree, and first egg of the season, when a severe storm uprooted the tree from its water-logged soil. For a storm to topple a nest is not uncommon for Bald Eagles, and I expected the pair to  get right down to re-building a nest (or to steal a nest from some local hawks) very fast. Why? Because there was every reason to believe there were more eggs to come, and very soon!

It takes about 10 days from the beginning of development until an egg is laid. An ova (an immature egg) needs a few days to ‘mature’ in the ovary, growing about 1,000 times larger. Once the ova is released it takes about three more days to travel down the oviduct to become fertilized, and then another three or four days for the membranes and shell to develop before subsequently being laid. Ova are released from the ovary about every 3-4 days, so with the first egg laid on February 10, that meant egg the second egg would have been released from the ovary on February 3rd or 4th, and the third egg would have been released from the ovary somewhere near the 6th through the 8th of February—before the loss of the nest.

Once the egg is released from the ovary there are only two (good) options: lay the egg, or resorb the egg; if one of these options does not happen a serious condition called egg-binding can occur. So, it is highly likely that the second egg was laid, and abandoned, as there was no nest to use for incubating. The reports of what appear to be incubation activity would likely represent the third egg, and be part of the first clutch. So far, the Hays female has laid three eggs in each of the years they were viewed with a nest camera, so there was reason to believe she would have three eggs again.

In the rare instances when eggs are removed, or lost, from a Bald Eagle they sometimes re-clutch. However, this involves a hormonal surge to prepare the ovary to mature an ova and release it, plus the week or so it takes for the egg to travel down the reproductive tract before being laid, so there is quite a delay in the laying of a second clutch.

I doubt there will be another egg, representing a fourth, but the disruption in the nesting season, followed by the hormone-boosting nest-rebuilding could theoretically lead to the maturation of more ova. However, this represents yet another problem. If another ova began maturing and was subsequently laid there would be a big gap in the timing of the hatching of the egg from the first clutch and that of the second clutch. This would lead to the probable demise of the second-hatched chick due to siblicide, as older, larger chick would dominate the food. There is no evolutionary advantage to this scenario, as the second clutch would be costly yet unlikely to yield a benefit, hence my doubt that it will occur.

Francis Herrick, who pioneered the use of blinds to study nesting birds, reported back in 1932 that Bald Eagles can build a nest in as little as four days, which is exactly how long it took the Hays pair to build the nest they appear to be using for incubation. I suspect this rapid nest-building is an adaptation for exactly this type of situation, and in cases where nesting season is farther in the future, they take their time building the nest.

For the remainder of this season the Hays fans will have to rely heavily on ‘trail reports’ for information, as the camera can not be moved to another location now. This would disturb the birds and is illegal. PixController is able to give you a glimpse of the nest through the trees from the current camera installation.

What a wonderful learning opportunity these nest cameras represent! If you want to learn more about what is inside an eagle’s egg, or how they develop, check out these sources:

Which came first, the chicken or the egg?

Eagle eggs, when and how they develop

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