Do Bald Eagles Reuse the Same Nest Year After Year?
The answer is commonly yes but the eagle territory often houses two or three alternative nests. I use the word ‘territory’ here because this concept is really more important to eagles than the specific nest. A breeding territory for eagles only houses a single active nest each year. On the other hand this territory may contain several nests that are alternatively used.
Most active eagle territories support a single nest that is used year after year. So why do some territories supports alternative nests and others don’t. Good question and no single answer is likely applicable to all circumstances. While a good solid undisturbed 600 year old conifer may support or have supported an eagles nest for 100 or even 200 or more years, most nests don’t last that long. And certainly the breeding pair of eagles don’t last that long. It is believed that eagles can live 50 or more years. Most don’t. While many conifer trees can live several hundred years most don’t and most deciduous trees live under 100 years.
So what causes eagles to move or abandon one nest and build another? Obviously if the tree topples or is sawed down they are to start over. It also appears to me from intense observations but observations on “unbanded” birds that when a mate is lost, the re-use of that territory with new partners often results in the building of a new nest. Perhaps mates don’t wish to settle in with a new mate in an old nest! Me thinks that is the way it is with wives!!
I believe I have witnessed the above reasoning on many occasions. In a couple of instances the original nest was located very close to houses or human disturbances. Perhaps the new partner simply was not yet so accommodated to human activity.
Another common case for new nests is when the eagles observe human disturbance near an old nest or someone up or near the actual nest cup. I have seen a nest abandoned when kids were seen climbing in the nest tree. It can be when biologists climb the tree to band the young. It can be when electrical power company workers get too close to a nest. And recently I have seen people installing cameras into bald eagle nests when the eagles were watching. On every one of these occasions the eagles opted to build a new alternative nest. The key in all these examples seems to be the eagles saw the human intruders in or at their nest site.
In some areas, like our urban environments, where alternative nest trees or artificial structures are few and far between there may not be any satisfactory alternatives and the eagles will stay nesting in a disturbed site.
Another cause for initiating a new nest is simply when the old nest supporting branches fail. The nest can result in supportive branches simply dying and breaking off. I am sure in some of the cases I have witnessed that the annually growing nest simply outgrew the strength of the branch and the nest weight broke the branches.
How Long to Rebuild?
A pair of eagles can construct what appears to be 4 – 6 foot (1.2 – 2 m) nest in a little more than a week. This does not mean the nest is finished. In fact the nest will generally be added to from the adults arrival back at the site right through until the young are fledged. I have even seen eagles working on two nests at the same time. Whether there was a competition for a favored site I am not certain. In the end the pair had two nests but laid eggs and reared young in only one.
In several instances I have seen sizeable and useable nests get built from nothing in less than two weeks. At this point the birds were seen in the incubating position and presumably had eggs or were about to have them.
So in summary: eagles tend to reuse the same nest year after year but some pairs seem to more frequently shift to an alternative nest than others. When a nest is lost or disturbed the pair can, if they find another structure capable of supporting a nest, build another one within two weeks.
David Hancock
HWF