Bald Eagle Nesting Influence of Avian Influenza?

Notes and Updates from HWF
Post Reply
Posts: 108
Joined: Apr 21, 2018

Bald Eagle Nesting Influence of Avian Influenza?

Post by davidh » Tue Mar 28, 2023 3:08 pm


Bald Eagle Nesting
Influence of Avian Influenza?

The 2022 bald eagle breeding season in the Greater Vancouver area was decimated with dying eaglets – and this following the “heat dome year of death.” In some regions less than 25% of the active nests fledged young, down by nearly a half to some one-third in other areas. Why? The biggest and most obvious suspected culprit was the ‘westward advancing Avian Influenzas epidemic’ hitting wild and domestic birds. But was this true? I write this note of a particular series of nest records for which we also have good backup observations by keen Raptor Monitors and our Live Streaming CAMS in the central nest. What I want to solicit is some observations from other nests in the region and from other regions. What we were not able to get were many analyzed bird remains. The analysis labs were tied up testing commercial chicken flocks and with the covid analysis delayed by human layoffs.

The Local Story Background:

Our White Rock nest with two streaming CAMS has been functional since the pair moved to our artificial nest in 2009. The landowner and sponsor of the CAMS, Russ Cmolik, has not just been a wonderful supporter but a superb note taker. Additionally, the Hancock Wildlife Foundation has over one hundred volunteer eagle nest monitors tracking many nests throughout the province and specifically in the Fraser Valley and our City of Surrey – and on our Live Streaming CAMS. We love our eagles.

The following is our summary of the 3 nesting pairs adjacent to our White Rock nest. Each pair is nesting less than 300 m from the central CAM pair, along one of the world’s most productive bald eagle coastal shoreline habitats, Crescent Beach, bordering Boundary Bay in British Columbia. Over 150 nesting pairs of bald eagles frequent this bay between the Cities of Surrey, Delta & Richmond.

Most incredibly, we are also the winter home for tens of thousands of wintering eagles, who stop here to avoid the northern freeze up of all their northern lakes and rivers. Here they fatten up before returning north to breed across the boreal forest and tundra lakes. Yes, the implications of this AI spread have huge potential international conservation impacts!

The Challenge:

Spotting dead chicks in or below bald eagle nests these past couple of years of Avian Influenzas has been difficult in most eagle habitats.
Here, in Surrey many nests are under constant watch. What is happening? Here is a specific story about the best bald eagle habitat in the world. We were unable to get many of our dead chicks tested so we are working on minimal testing results and counting on more observational records coming into us. We work closely with the Provincial Wildlife authorities and the Federal Canadian Wildlife Service, but authorities put other priorities above eagles for specimen analysis.

The facts we know:

1. The White Rock nest, (WR nest or 040H), is internationally known
due to our 15 years of live CAM broadcasts streaming from the nest. Many of you will recall the dozens of Streaming broadcasts Christian Sasse (Sasse Photos) and I did on site. And additionally, we featured this nest in our David Suzuki CBC and PBS distributed film. Additionally, many of the regionally trapped eagles that carry our ‘trackers’ have their life’s travels posted daily to our web site – and many visit this ‘food factory’ along Boundary Bay. This particular year 2022, the eagles finished building a nest they had started about 4 years earlier, less than 80 m from the CAM nest and known as the WR Peace Tree Nest.

2. Into 2022 this WR Peace Tree nest
had both chicks die at about six and a half weeks of age. This could be observed from the WR Cam located about 74 m from the new nest. Both nests can also be viewed from the roadway.

White Rock deceased eaglets in nest
20220615_WhiteRock_Amyklai (002).jpg
Photo courtesy of Amyklai

3. The adjacent nest to the north,
Nest 040.5A, also had a chick die in the nest at about six weeks of age. This was also readily observed from the roadway.

4. The adjacent nest to the south,
Nest 403B, possibly suffered a similar fate. One of the two chicks fell from the nest at about 10 ½ -11 weeks of age (just a week or so before fledging!) and died that night but not likely of falling injuries. It tested positive for Avian Influenza at the OWL Rehabilitation Center in nearby Delta – the recovery center for all local raptors.

5. Then biologically the story gets even more interesting:
all three adult breeding pairs abandon their nests just before or at the fledging time. Shortly later some are known to start new nests (403) or revert to old nests (049F) or possibly not even return (040.5). It is possible that the 040.5 adults died! Did the other or all pairs realize something hard for us humans to comprehend? Did they understand that these deaths were indicators of a “bad nest,” a nest to be avoided next season?

6. In the new 2023 season all three original 2022 nests are deserted.
Wow. What - do they really know this from seeing their chicks dead? Only rarely do eagles move to new nests. My evaluation is that they stay in safe nests and only move when they perceive some temporary or long-term nest threat. This is usually a human nest intrusion or the breaking off of a supporting branch and the nest slumping – if it does not fall altogether. I have followed more that a 1,000 nests, many individually for over 30 years, to feel confident in that statement. But that data is another story of my life.

The Question is: “What can we derive from this and ancillary data?”

In part I am writing this to also seek your thoughts and experiences on this recent impact. Do you have observations on nests near you? I would appreciate hearing from you.

What we learned from the OWL and the Provincial and Federal carcass analysis is more interpretive than statistical. Avian Influenza was a big killer of raptors including bald eagles. Did our thousands of migrating eagles, including our nesting adults and reared nestlings that also regularly fly to Alaska spread the disease to a wider population.? Has the AI epidemic caused any long-term reduction in migrants or the local population? Were any age classes, different juvenile or adult ages classes affected differently? Only time will tell if fewer birds return in the coming years or the recruitment to our breeding population is slowed down. Oh how I wish we had more eagles carrying our Trackers.

Sadly, I do not see determining any percent loss due to AI - as would be nice to summarize. So far, the data is suggestive but not adequate.

But we did learn a huge amount about bald eagle biology:

1. Our three local territorial breeding pairs , 040, 040.5 and 403, revealed a lot about eagles.

2. First, our geographically most closely breeding pairs all suffered eaglet deaths.
This suggests that the problem of AI may well be highly transmissible to eagles during the breeding season. But where or what was the common infecting site or prey? Was this due to communal feeding at places like the local landfill, or feeding from the huge midshipman breeding grounds below the eagle nesting cliffs? Or was it something else entirely?

3. The next nest to the far south (1.8 km away) did not suffer losses giving a kind of comforting reinforcement.

4. The next nest north was 980 m away – had no young again giving similar support
but we were not sure which of several alternative nests was used in 2022. Some nests are just very difficult to observe – even with keen Monitors.

5. Big conclusion of three adjacent nests:
all three nests suffered losses BUT possibly all three sets of parents decided to get new nests the following year. Did they understand the loss as sufficiently disturbing to move a ‘little bit’ away? Quite a common, yet local response. Also, is this nest relocation a built-in survival strategy? Is this an evolutionarily learned behaviour? All implications again point to the incredible adaptability of bald eagles. Since our bald eagles apparently evolved from old world vultures who you would have thought could have historically encountered such diseases, this suggests that possibly this Avian Influenza is relatively newly evolved. Maybe that is a bigger jump than warranted!

We look forward to your pertinent observations and images. Getting on top of bald eagle and other raptor mortality is always challenging, yet exciting.


David Hancock, HWF

Post Reply

Return to “Monitor Updates”