June 20, 2023
I was recently queried about the movements of our two distinct western populations of bald eagles. Here is my response:
We, here in southern British Columbia, are about to lose ALL of our breeding eagles and their young. Fledging and the fall migration is about to begin. Most of our followers know the fledging is just about to happen and that instantly, well, with a week or two, initiates the fall departure to the northern pre-set banquet.
Nature has had millions of years to adapt to the most efficient use of its diverse energy sources. Our coastal and our northern eagles represent a fine-tuned example of how both our southern and northern related cousins have adapted to the natural seasonal availability of food.
The feeding pattern of bald eagles is quite consistent, a pattern flowing from their evolution from old world vultures – walkers and visual hunters. Our bald eagle evolved fish-grabbing talons and this enabled them to move away from the need for year long huge veldts of large constantly dying ungulates of Africa or India and move to all the shorelines of MUCH of the world where fish were available year round. Ten species of fish eagles have occupied most of the world’s shorelines except South America.
The interesting thing about this evolution is that several of the bigger fish eagles and those with the widest distribution all have retained for about 1/2 the year their ancestral habit of “scavenging.” Why waste 6 months on hunting if you can pick up free dead food? For our bald eagles this is their non-breeding season “almost exclusive” feeding style. After a nesting season where they are spread out along shoreline of lakes, rivers or sea, where they predominantly catch small live fish that they are capable of carrying to the nearby nest, they initiate a migration that permits them to follow their old ways of scavenging all fall and winter. Our bald eagles spend their fall and winters largely living on spawned out salmon – from the early northern runs starting in mid June through the southern run ending after January.
Certainly the scavenging habit can be utilized during the summer breeding season. This is when they readily diversify to eating small road kills in the urban and rural areas – scavenging dead rabbits, rats, etc. and in our lower mainland picking up the dead male mallards that were waiting for their nesting females to come off the nest for a little nookie. The mallard’s behaviour suggests that some don’t learn that cars tend to win the encounter. This scavenging, supplemented in a few areas with goslings, ducklings and muskrats, is a good complement to catching small cartable fish for the nestlings.
So our local nesting eagles predominantly catch small fish, indeed often specializing on midshipman, through the nesting season and revert to their exclusive scavenging ancestral habits post fledging for the late summer and fall period when the early salmon runs of the north entice them to the northern rivers. That northern banquet is nicely set as our southern nesters finish up rearing their young by the end of July and so they, and a week later their kids, fly to the northern rivers for the spawned out banquet waiting for them. Then, our southern breeders, along with the really big northern eagle breeding population, get driven out of the north as freeze up forces them all south.
What a wonderful coincidence that our local salmon are now, November through January, piling up on our unfrozen rivers of the Harrison and other regional streams. We get about 35,000 to 50,000 eagles each fall in the lower Fraser. This is, of course, the attraction for our annual Fraser River Bald Eagle Festival. This completes the seasons: a fall and winter of scavenging dead salmon, and a spring and summer of catching fresh fish for the kids. The biggest population of bald eagles breeds across the fish-filled lakes of the boreal forest of northern Canada and Alaska. But, we at the mouth of the Fraser River and along the shoreline of Southern Vancouver Island also have some of the most productive bald eagle nesting habitat in the world. A big reason for our motto: Super Natural British Columbia!
I think most of our web site followers already know this from direct observations. However, many have not clearly understood the two very distinct populations of eagles, with their different migratory patterns, that occupy our coast. Our efforts at tracking these eagles, supported by your funding, is greatly adding to this understanding. Thanks.