Chat Moderators > Decorah Eagle Mods Want You To Know -- Eagle Education

All About Nests

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We're opening up a new thread for discussion about Bald Eagle nest building and nest restoring.  We will be opening these threads in chronological order starting with nestorations as mom and dad have begun light nest refurbishing.  A reminder:  as stated in the "Posting Guidelines," we ask that you limit your posts and comments in this thread to this particular topic.  We hope you join in the discussion and look forward to your participation.

Bald eagles show a strong fidelity to their nest sites so they may use their previously built nests year after year.  Both male and female will usually start restoring their nest 2 - 3 months before egg laying season though the work isn't constant. They add sticks, grasses, mosses, corn stalks, vegetation and any available materials they find suitable.  In most cases the pair will add and intertwine sticks to the sides of the nest, in a woven pattern around the nest's rim. The sticks used for the outer rim of the nest are usually larger and stronger which provide a sturdy wall around the circumference of the nest. Softer materials are brought in for the nest floor and most especially for the nest cup or bowl which is the last phase of nest refurbishing before egg laying takes place.  Scott Nielson calls bald eagles "compulsive nest builders" that they will rework last year's nest, no matter how sturdy or complete it looks to us humans!  They will also add some materials during nesting season. Some scientists believe that adding greenery may show that the nest is taken and to keep intruders away.  Others have stated that it could serve as an insect repellent or provide some camouflage. 
Nest restoring, or as we affectionately call it, "nestorations" can add significant weight to the nest yearly.  It has been estimated that a nest generally gains approximately 200 pounds per year, which includes any prey remains as that eventually becomes part of the nest as well.  A bald eagle nest on the shores of Lake Erie was used for over 3 decades and was found to be 8' across and 12' deep and estimated to be about 2 tons in weight before it fell in a heavy storm in 1925.  It was only to be outdone by a bald eagle nest in St Petersburg FL at 20' deep and 9 1/2' across.  This particular nest weighed in at over 2 tons as well.  It toppled in the 1970's due to excess weight.  It should be pointed out that the examples of these 2 nests were most likely constructed and used by more than one generation of eagles, piling materials on to the nest decade after decade. 
 A mated pair's teamwork in nest restoring is also a bonding behavior. It helps strengthen and cement their bond to each other and brings the female into breeding condition.  A particular action such as united stick moving is actually a common bonding behavior.  Here is a video of Decorah female in the nest and Decorah male bringing a stick.
Here is an article on the Iowa DNR  collecting data on eagle nesting territories in Iowa as of 2012.  The study also provides a map of all Iowa counties where the 1st bald eagle nest was reported during the specific year indicated since 1977.   The DNR received a grant in 2012 to do a training video for bald eagle nest monitors. 

Outstanding as usual.  Thanks Finn and jfrancl.

Finn, you wrote the following:  "A recent study by the USFWS showed that--in the Upper Mississippi River Valley area--bald eagles predominantly chose cottonwood trees with swamp white oak or red oaks running a distant second."

This choosing - is it based on an eagle's knowledge of individual tree characteristics and they choose accordingly - or is it a simple matter of what kind of trees are available?  Making a choice indicates to me some awareness of what tree to use - is that possible?  I hope I'm not underestimating the intelligence of eagles. 

And by the way - this is a great topic!

Thank you Finn - I really appreciate your response.  The bald eagle is so darn smart!

One thing that just amazes me is how quickly all those dead, dry sticks and other nesting material add up to such tremendous weight.  I mean heavy enough to topple a tree!  Some raptors we have seen build nests on man-made structures although I suspect that leans towards smaller nests.  But, is there any record of bald eagles building nests on man-made structures?  Are there structures built for the sole purpose of attracting bald eagles to build a nest?  Having said that perhaps there is no need for man to provide such structures. 


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