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Hi Raptor Monitors,

Challenge: If different people view different species at the same nest – who is correct? Obviously, both are likely right. Only time and more observations, however, might convince both monitors who is the nest owner. Here is an example.

RE: Territories: Nests Su-513 and nearby Su-401

The challenge for me is that for the past six years various people have seen both red-tails and bald eagles ‘reported’ nesting in both the 513 and 401 nests. And of course, both conclusions are valid. Both monitors know their raptors and made valid recordings. The observers, initially, were not so sure of this broad conclusion. Here are some thoughts!

I had also seen both species in each of these nests several times. So, what is the explanation? After many long years of observing nesting raptors, I see some logical options. I am now convinced one frequent resolution to these conflicting observations is more commonplace than obvious. In several of the above sites I saw birds of both species hunkered down in the incubation position – but generally in different years. The species seasons overlap.

Basically, the early ‘little nests’ were built and occupied by the red-tails. A later, ‘bigger nest,’ was the product of the eagles adding much additional materials to the smaller platform so conveniently started by their little cousins. This of course is a simple “after the fact kind of conclusion”!

Starting a nest is a major challenge to all the big birds but bringing in big enough support branches is even more challenging for the structural demands of an eagle nest that might eventually reach 400 or 500 pounds. Eagle nests, when the tree structure permits and lives long enough, have weighted up to a ton/tonne. The challenge for the eagle is getting solid enough branches that will span between at least the two key support branches. I have seen some eagles try unsuccessfully to place these first branches. I am now more amazed that they ever succeed rather than occasionally see them fail. In the Fraser Valley I have found nearly 40 percent of the eagle nests in deciduous trees were started by red-tails. Even four of my nine current hydro towers were initiated by red-tails. Our adaptive eagles know a good thing when they see it. Their challenge is not finding enough adequate stout branches high enough up in the trees within their territory. And the red-tails have lots of smaller options. So, both survive.

The eagles’ challenge of finding the right base of a strong branch structure to start with is what has prompted me to initiate building nests for them. We can place incredibly strong foundational branches in crotches we supplement that allows us to then add additional branches, gradually growing upwards the platform to support the 1.5 to 2-metre-wide nest that we offer them to start with. In fact, I am writing a book about how to build eagle nests and where to place these artificial nests. 

The key is to offer the eagles what they would naturally find in unforested lands. Where we humans have removed all the old solid big trees, particularly the conifers that have stronger and longer living branches than the soft and quickly rotting cottonwoods, we can ‘spruce up’ inferior smaller trees to support the huge nests. Sometimes we actually build a temporary nest, one we suspect might only last 2-3 years, to hold a breeding pair in their territory until we have funding or time to locate a more permanent nest; at last resort a pole & nest.

An aging cottonwood is shedding branches as it ages and is not likely to survive 150 years. Some conifers can readily support nests at 60 years and live 600 or 1,000 years. In our heavily forested and built-up areas few trees remain that contain the big branches to support a nest. Most eagle nests fall from the tree in the first year or within five or ten years. On our website is a sprightly young conifer that was cut, measured by its rings, at 668 years, and could have already supported the existing nest 450 or 500 years. That cannot happen with cottonwoods. We have to make up the interim supportive structures to save their homes or provide places for new homes where the big trees have long ago been removed.

If you are following many nests, you will have noted that in the logged off areas it is the more fragile black cottonwoods that pop up quickly along road and creek sides. In developed areas most eagles, or for that matter red-tails, build in the available cottonwoods.

Simply few of the stronger conifers still exist. They were either removed to provide space for our buildings or farmland or they were blocking a view. In either case they were not available for big raptors to nest in. An obvious “best management practice” is to provide extra trees for the long term and in the meantime supplement existing trees with stronger supports. Or, where there are no trees to modify, then we put in a pole and nest.

So far, we have never had a development remove an eagle nest that we had not come up with an option to keep the eagles continuously nesting. This tool is conservation-in-action We are now exploring ways to get eagles into artificial nests in territories no longer presently holding any of the required big trees.

My Fraser Valley observations suggested the bald eagles were commonly usurping the pioneering red-tails’ nests in a big way. It is common to see the smaller red-tail at the crotch base with the bigger eagle’s nest simply built on top. I have recorded that nearly 40 percent of the lower mainland eagle nests started out as red-tail nests. This is how our D2 CAM nest started. I first observed the red-tail nesting for several years, then the eagles eating the red-tail chicks. After the eagles migrated, I entered the nest to see the results – the red-tail’s chicks were all gone. However, I could see that the nest was falling down and I inserted a few large timbers to give more lasting support.

The following year the eagles moved and expanded the nest for themselves. The five cases of BAEA’s adopting and raising RT chicks we have followed is another related case of the eagles interacting with red-tails – not always to the little hawks advantage. Perhaps finding the dinner is considered an invitation to move in for a longer stay!

The conclusion is logical – and perhaps more common than we have understood. Red-tails are good home ‘starters’ for eagles as well as providing less frequent direct meals. Of course, more frequently eagles rob red-tails of their little rodent dinners. Interestingly, they both remain a very common nesting raptor in our valley.

From the legal Wildlife Act perspective, both specie’s nests are protected, but the eagles get ‘all-year-round protection of their nests’ while RT in reality only get nesting season protection. BUT once an eagles nest “always an eagles nest.” Back to our opening comment: knowing the truth on who is nesting where in any specific year is more complex than many observers have initially understood. I appreciate getting any and all the detailed notes and images to fill in the picture to make the correct decision. Multiple observations help separate out nesting vs predation – not easily or always concluded by one or two visits. And more interestingly, predation seems to sometimes be followed by residency! Getting as many observations as possible per year per nest is key to keeping this straight.

If any of you want to be monitors and wish to contribute notes or new nests to our expanding database, now 680 nests in the lower mainland and more elsewhere, give me a call and I can supply you maps of your region of interest.

Special Note: Did avian influenza or the earlier ‘heat dome’ affect eagles or raptors in your area? If any of you noted or have photos of dead chicks in the nests, please send them to me. I am trying to better understand what happened the past two years and if what we observed in the lower mainland is more widespread. Your comments and observations will greatly help build this picture. That is the next note I will be posting.