About us: We own the Wild Birds Unlimited nature shop in East Lansing, Michigan,
a store that provides a wide variety of supplies to help you enjoy the birdwatching hobby.

This blog was created to answer frequently asked questions & to share nature stories and photographs.
To contribute, email me at bloubird@gmail.com.

Saturday, April 27, 2013

What happens if the female bald eagle loses mate while incubating eggs

Hi:  I have been watching live streaming videos of Eagles' nests and the parent sitting on the eggs, on the Hancock website. I have observed the eagle parent leaving the two eggs unattended in the nest on a regular basis, every day, about 5-6 PM. I presume that the Eagle parent is off looking for food, and I have not seen a second parent eagle since nest-building time. The eggs are left uncovered for up to 60 minutes. Is this common behaviour and will these unattended eggs hatch? Thanks, Joan

The amount of time eggs can be left alone varies on the bird species and weather conditions.

Once a female Bald Eagle lays her eggs there is a 35 day incubation. Both the male and female take turns protecting the eggs and keeping them warm. The eggs are covered 98% of the time, but it is the female who spends most of the time on the nest.
  
The male does more of the hunting and provides some food for the female. If prey availability is low, or the female needs to take a break, the eggs can be left for up to an hour depending on the weather. Severe low temperatures could leave the eggs nonviable.

If both parents must leave the eggs frequently or for long periods, chances for successful development and hatching are reduced. For this reason, it is very important not to disturb any nesting birds.

During the early incubation period, the female turns and rearranges the eggs with her bill to ensure even development and prevent internal material from sticking to the inside of the shell. The female also develops a temporary loss of feathers on the belly, called a brood patch. This allows the bird's bare skin to come into direct contact with the eggs and keep them very warm.

As the days progress, the eggs lose water and an air-filled space at the end of the egg develops. This is where the chick draws its first breath before breaking through the shell. By the time the chick is ready to hatch, the eggshell is thinner because the calcium from the egg is incorporated into the skeleton of the developing chick.

As hatching nears, the chick begins calling softly from inside the egg. The mother answers the chick and doesn’t leave the nest during this period.

Hi:  Thank-you for your prompt reply. I have followed this nesting Eagle pair for about 3 years and have become quite attached to them vicariously. So I notice that the nest and eggs are left unattended a few times each day this year. It appears that one mate is no longer alive. My question is, if the eagle eggs are not going to be viable, will the parent eagle sit on them anyway for a prolonged period of time, and is there a way for the eagle parent to "know" that the embryos are no longer alive? If the eggs are not going to hatch will the parent eventually leave them after a certain period of time? Thanks, Joan

Female Bald Eagles seem to be the ones who choose the territory and the nesting tree, because when a female loses her mate, she usually very quickly attracts a new male, even if she's already sitting on eggs fertilized by her first mate.

Eagles are very dedicated parents. They do not know if an egg will hatch or not. Instinct will tell her to continue to incubate her eggs until they break. This process could take a couple months. If the eggs don't hatch, she’ll probably remove each egg after they disintegrate and then leave off nesting again until next year.

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