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[jfrancl]

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.

[jfrancl]

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.
 
http://www.youtube.com/watch?v=s3SJwp7dXQM
 
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. 
 
Article:  http://www.iowadnr.gov/Portals/idnr/uploads/wildlife/research/BENestSummary_2012.pdf
 
Video:  http://vimeo.com/46365137

[ThinkingWoman]

Outstanding as usual.  Thanks Finn and jfrancl.

[Bob1603]

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!

[Bob1603]

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. 

[Bob1603]

"One theory is that BEs aren't as adaptable as other raptor species--that in the wild BEs are programmed to choose trees with the characteristics that help them to thrive and survive--height, nearness to water, protection from the elements for their nest, etc. And it would be hard for a man-made nest to meet these particular criteria."

As I have said before, eagles know more about eagles then we do.  Amazing creatures!  They do things we humans can only dream about. 

[jfrancl]

Bob,  though I don't have data on recorded artificial BE nest construction and  usage success, I do have a link to an artificial nest construction and illustrations from the USDA Forest Service.

http://books.google.com/books?id=9IvjoVbe0R4C&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

[Faith]

Thank you Jf and Finn.  Great info as always!

[Bob1603]

Nest building.  From the time the eaglets are hatched, grow, and then fledge they never see their parents build a nest.  When the juveniles reach the point of selecting a mate and are ready to start a family, how do they know the techniques it takes to build a nest?  Do they learn by observing other eagles build one?  Does their instinct kick in and they just "know" how to build a nest?  Am I asking a question with no answer?  I'm pretty sure there isn't a Nesting Building 101 class for them.  Do they self-teach through trial and error?  How do they know?  I bet its that thing called "instinct."

[Bob1603]

Bob,  though I don't have data on recorded artificial BE nest construction and  usage success, I do have a link to an artificial nest construction and illustrations from the USDA Forest Service.

http://books.google.com/books?id=9IvjoVbe0R4C&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

Thank you jf - thats a pretty cool and very informative article. I wonder how many of those nests the USDA Forest Service has built over the years and if they are still putting them up.  It would be interesting to know if any are still in use.  Thanks again.

[glogdog]

Bob - great question!  Though I've looked in a few books, I am not finding the direct answer quite yet.  I'm sure Finn and jfrancl will comment on this.  I am finding some other interesting info which makes me believe that perhaps it is "instinct" or an "ancient pattern of behavior" that kicks in when it's  time to build a nest.  As jfrancl stated earlier, Dr. Scott Nielsen in his book, A Season With Eagles, states that, "Bald eagles are compulsive nest builders". Gary Bortolotti in his book, The Bald Eagle, Haunts and Habits of a Wilderness Monarch, states, "Even immatures may be involved in nest building" which concurs with what Pagent said. Scott Weidensaul in Raptors The Birds of Prey, states "As a rule, raptors tend to nest in the same kind of habitat and site in which they themselves were raised."  He also says that "twigs, sticks, and branches are the material of choice for the bulk of the structure."  As far as length of time to build the nest...Golden Eagles may take from 5 days to 2 months whereas an Osprey can have a new nest ready in 2-3 weeks.  In his book he also says that the Bald Eagle makes what are probably the largest nests built by single pairs of birds, and they are the heaviest.  Our Mom & Dad started building N2 approximately mid-October 2012 and were pretty much done within 6 weeks or so I believe.

[jfrancl]

Bob, Pagent is correct, they commonly do build practice nests.  Juveniles still in the nest will also imprint on the nest they are being raised in.  Nick Fox states that they imprint on nest type, as glog stated, site and habitat and their peak nest imprinting stage begins during the development of their second down.  Once fledged, the eaglets imprint on the surroundings of the nest such as trees, cliffs, man made structures such as white barns! lol.  Fox states that there is a strong correlation between the type of nest a chick is raised in and the type they will choose as adults.  So your questions actually fit into both the All About Nests and Imprinting threads!

As far as how many nests the USDA Forest Service has built and the success of the nests, that would be a great research project for you!

[Faith]

Regarding Bob's question, it comes to my mind that though the eaglets don't see the parents build the nest from start to finish, they do observe the parents bringing in new sticks and nesting materials in their ongoing nestorations.  We have seen eaglets "play" with these materials and imitate what their parents do.  This could be part of the foundation for their learning how to construct a nest.  I suspect that instinct has a lot to do with it, as well as imprinting on their parents and environment.

[jfrancl]

Agree Faith, I think both instinct and imprinting play a part

[Bob1603]

Bob,  though I don't have data on recorded artificial BE nest construction and  usage success, I do have a link to an artificial nest construction and illustrations from the USDA Forest Service.

http://books.google.com/books?id=9IvjoVbe0R4C&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

I have an email in to the author of that pamphlet with questions about the artificial nests but I have not heard back from him yet.  When I do I will post his response.