Raptor Resource Project Forum
Chat Moderators => Decorah Eagle Mods Want You To Know -- Eagle Education => Topic started by: jfrancl on October 25, 2013, 12:02:39 PM
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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.
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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
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Outstanding as usual. Thanks Finn and jfrancl.
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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!
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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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"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.
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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
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Thank you Jf and Finn. Great info as always!
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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."
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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.
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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.
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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!
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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.
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Agree Faith, I think both instinct and imprinting play a part
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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.
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Bob, that's great. I'd be interested hearing any data he may offer. Hope you hear from him!
And thank you for posing some very interesting and thought provoking questions!
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Isn't learning great? Information brings up questions, more research, more questions, and more research. We can learn something every day and still not know it all! I love this Forum board!!
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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
As I stated earlier I sent an email to the author of the pamphlet mentioned in the above link - here is his response.
Bob,
Thanks for your interest in artificial bald eagle nests. The tripod structure described in Research Note 383 was a unique structure built specifically for a nesting pair here in Arizona. There's a follow up article published in the Journal of Raptor Research (1983; pdf attached) that describes the rather unusual use of this structure as the original lake bed flooded a couple years later. Those flood waters eventually washed the structure away. Since then we have much improved our approach to constructing artificial bald eagle nests. See attached pdf for Research Note 535 (1995). This latest article includes a summary table for AZ, CA, and WA artificial nests, but as far as I know there is no centralized tally of all the nests that have been built over the years around the country. It is not an uncommon practice. I have helped build or consulted on the construction of nests throughout much of the bald eagle's range. Plus the US Fish & Wildlife Service in East Lansing, MI, has developed plans for a different style eagle nest with a platform constructed mostly out of 2x4 lumber attached to the new nest tree. A number of those have been built in MI. Successful use by eagles remains very much a 50:50 proposition, as they can build their own nests within a week or so if they want. Using artificial nests like 'bird boxes' to encourage nesting is an even less likely endeavor. The greatest success comes from the replacement of a fallen nest or nest tree. I hope this information helps answer your questions. Thanks again for your interest!
Teryl G. Grubb
Mr. Grubb states that "Successful use by eagles remains very much a 50:50 proposition." That is a percentage that I feel is pretty darn good because any eagle in any nest is a success. He also mentions two other publications and I will try and get links to those.
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Bob, unfortunately the links aren't working for me. Anyone else? Is it possible to remove the "s" from https? Not sure if that will help.
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I have some problems posting access to the Grubb publications in the Forum. 1. The URLs I have for the publications simply will not open - even after removing the "s" from http. 2. The publications are too large to post here because there is a limit on what the Forum will allow - even when I tried to post them one at a time. Emailing them directly to a Forum member works fine so please let me know in a private message if you would like me to send them to you. Thank you.
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Here in central Alberta, winter is settling in and our eagles have headed south. My question is this.
What impact does their absence from their breeding territory for the 5 months or so have on the nature and quality of their nests, bonding, etc.? Is it different than that of eagles that remain in their territory year round?
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Emyrauld, BEs have a very strong nest/nest site fidelity. So provided that there hasn't been a take over upon returning, they would just resume nesting and breeding activities.
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jfrancl: In watching eagles at Decorah et al, it would seem that a fair amount of time and effort goes into nestorations at this time of year. If the eagles aren't around to do it, I just wondered how they compensate for the lost time, or if they simply miss out? We are experiencing overnight lows of -10 C (14 F) so our rivers and lakes will be frozen over shortly. I am pretty sure those that have not left already will be gone soon. They return early to mid March and eggs are laid mid April, I am told. That's a lot of nest reno time lost. I am just curious.
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Emy, pretty cold there! Brrr
Right now our Es are in a phase insensitive to light, opposite of the photosensitivity period and hormones haven't spiked yet. So the nestorations are minor now and will progress as time goes on. They do bond during this period but wont go full force with nest restoring until mid/end of Dec or so. And they can get nestorations done in a very short period of time if they had to. BEs can build a nest in 1-2 weeks if necessary so nestorations can be done quickly.
Thanks for participating in this thread and your great comments!
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Average spacing of active BE nests in SE Alaska is about 1 active nest for every mile of shoreline or coastline.
In Florida nesting territories can range from .6 - 1.2 sq miles. Bald eagle nests are spaced apart to ensure sufficient food for nestlings and minimal disturbance from other eagles.
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In The Bald Eagle, Gerrard and Bortolotti, it states, "As a species, the Bald Eagle appears to be an adaptable bird, even nesting on a giant cactus in Baja, California, a bare rock in the middle of a Saskatchewan river rapids, and a hayloft of a barn on the Niagara River." It further states that BE's are "highly selective as to where they place their nests". They generally build in dominant trees: big red and white pines in Minnesota, pines and cypresses in Florida and Douglas-firs, Sitka spruces, and cottonwoods in Alaska.
The actual tree has distinct qualities. "The Bald Eagle prefers a more secure site in the crotch of a tree sheltered from the elements. An eagle's nest tree is usually alive but often has a broken, deformed, or a dead top. Nest trees, regardless of their species, are stout for their height and large crowns." It also says they will have a spacious canopy which is advantageous for the adults during takeoffs and landings. The large crown provides a secure site in which to build a large nest.
Hey Bob - this part is for YOU. (Keep in mind this book is copyrighted in 1988). "Only a few Bald Eagles have nested on man-made nest structures. Sergej Postupalsky has witnessed some nesting attempts on platforms in Michigan. Eagles have accepted a large tripod erected by Teryl Grubb in Arizona to serve as a substitute for a nest that blew down. Similarly, eagles have used makeshift wooden pallet platforms to replace fallen nests." This is like the Sutton nest in Stillwater, OK. Here's a pic.
The book does go on to say that it is common to find 2 or more nests within the territory of a single pair of eagles. The last thing I want to add from the book interestingly is this statement: "Usually the active and alternate nests are within a few hundred yards of each other". Sound familiar? ;D
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glog there is a photo in RRP's blog of a mated BE pair that "own" 2 nests in one tree in MN
http://raptorresource.blogspot.com/search?q=alternate+nests
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That's right, jf. Thanks for reminding us of that! How interesting is that, huh?
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Bald eagles have to be among the most fascinating of creatures - multiple nests (some in the same tree), artificial nests, shared territories, - it goes on and on. You just got to love 'em!
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In thinking about N2, I recall Mark Stalmaster's breakdown of BE nest sizes and shapes. He states that BE nests can take on a cylinder shape, a bowl shape, a disk or an upsidedown cone shape.
Cylindrical nests usually are constructed between 2 upright branches that are paralel to each other. Bowl nests are "cradled" by supporting branchesas well as the tree trunk itself. Disk shaped nests are placed close to the trunk and placed above several branches mainly in one of a variety of pinelike trees. Conical nests develop where the configuration of the tree branches allow the nest to be smaller on the bottom and becomes larger as it reaches the top.
Here are some photos of N2 in the making.
https://www.facebook.com/media/set/?set=a.452176618152296.89585.103786266324668&type=1
or
http://www.facebook.com/media/set/?set=a.452176618152296.89585.103786266324668&type=1
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Do we know if Bob/Amy have been keep an eye on the Original Nest?? Is it still in a complete state of disrepair so we are pretty sure they will be using The Yonder Nest this year???
And thank you all for the information on "scraping" on another thread...I saw that commented on and had never heard of it before!!! Our Eagles keep me learning ALL the time!!
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Here's "The Nest" episode of the PBS NATURE series, "Animal Homes." Grain-of-salt warning: the filmmakers at NATURE are good storytellers, making a complex situation entertaining and easy to understand.
http://video.pbs.org/video/2365460608/
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Here's "The Nest" episode of the PBS NATURE series, "Animal Homes." Grain-of-salt warning: the filmmakers at NATURE are good storytellers, making a complex situation entertaining and easy to understand.
http://video.pbs.org/video/2365460608/
I love this. It is the first in a 3-part series about Animal Homes. I've watched "The Nest" twice already and posted news of it and how to locate it online in a couple of other Forum threads already. Glad you posted here about it. The 2nd in this 3-part series aired tonight - called, "Location, Location, Location." It shows different kinds of animal homes, and does include hummingbirds.
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Went searching for artificial eagle nests in Google Scholar and didn't find much, especially current info. I think RRP and Neil have a lot to teach the world about bald eagle nest reconstruction!!!!
This is a charming story of what the authors think is the first artificial (reconstruction) bald eagle's nest. From 1969.
https://sora.unm.edu/sites/default/files/journals/wilson/v082n03/p0326-p0327.pdf
And from 1980, here's a paper entitled: An Artificial Bald Eagle Nest Structure. It's radical and seems to borrow heavily from constructed osprey nests.
https://play.google.com/books/reader?id=Uqhjz7RBiPkC&printsec=frontcover&output=reader&hl=en&pg=GBS.PP1
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Thanks, Finn. At least we know there's nothing much new on artificial eagle nests! LOL
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In Amy's most recent blog post, she mentions 'T1' and "TNF". Someone please define. Thank.s