2/27/17 – Well, after dark this evening the Harmar female returned to the nest while no one was watching and she now appears to be incubating an egg! Since this happened after dark, when no one was watching, we will have to see if footage is available to be reviewed later, so it is unclear at this time exactly when this happened, but it seems to have occurred between 8pm and 8:42pm. EagleStreamer was kind enough to set up this HatchWatch Clock for us. If footage does become available I will be sure to pass it on for everyone.
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:
2/11/17 – You may already know that the Bald eagle nesting season in Pennsylvania has arrived! Both the Hays and Hanover females laid their first eggs of the season within minutes of each other on Friday evening 2/10/17. Because they are on live camera there is video of the Hays female laying her egg, with the male coming in to assist the best a male can in these situations, as well as the Hanover female laying her egg. The Hanover female has been incubating with some time off the egg, which is perfectly fine at this stage of development. The Hays female, on the other hand, has not been incubation her egg as much. She has not abandoned the egg, but it is possible she is attempting to delay incubation. This is a possible adaptive strategy aimed at assuring the first and second eggs hatch more closely together, thus reducing the size difference between the two chicks and potentially increasing the chances that both get enough food to grow rapidly. Delayed incubation was not previously thought to occur in Bald Eagles, but nest cameras have allowed scientists to witness nesting activity in ways they never could before. If you would like to contribute to a study of nesting behaviors of Bald Eagles by watching nest cameras, you can find more information about the Egalitarian Science study I am currently working on.
If you recall, the Harmar female generally lays her eggs a few weeks later than the Hays and Hanover females. Annette Devinney captured this photograph of the Harmar pair getting ready for the nesting season, thanks Annette!
Meanwhile, the Harmar nest had a visitor again this season, a Red-tailed Hawk was seen spending several minutes in the nest. It is impossible to know if this was one of the hawks that used to claim this nest, as several are frequently seen in the area. Thank you Dollyqueen and Jerseyme for capturing and posting the video!