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Saturday, January 31, 2009

Eagle Watch

After hearing some reports of a potential golden eagle sighting off the south end of the island, Jason and I decided to head out and investigate this morning. There are lots of erroneous reports out there about how relatively common golden eagles are in the San Juan Islands. The fact is, after 8 years of intermittent birding here, I have yet to see one. Birding in the San Juan Islands, a great book, talks about 5 known breeding pairs in the county, but that was in 1987. The authors mention that experienced birders feel the species was in a local decline at that time, and I wonder if they are really still here at all.

Juvenile bald eagles can easily be mistaken for golden eagles because they don't yet have their white head and tail. These juvies have white "arm pits", often with a lot of other white mottling on their underside, unlike the distinct white "elbows" of juvenile golden eagles. Adult golden eagles have no white on them at all, and feature a tawny wash of feathers over their head and neck that gives them their name. Another way to tell golden and bald eagles apart is by their wings in flight. Bald eagles soar with very flat wings, while golden eagles tend to hold their wings in a slight dihedral.

We sure didn't see any goldens, but we saw a TON of bald eagles, both adults and juveniles. They seemed to be just about everywhere. We easily saw more than 20 eagles this morning. Many of the adults are starting to pair off and we saw some aerial courtship behavior.

This was one of the only perched eagles we saw, as all the others seemed to be enjoying the strong winds in flight. It looks like a young adult, since its plumage still looks a little mottled as it loses its juvenile plumage. Bald eagles don't get their white head and tail until they reach sexual maturity in their fourth year.


Here's one of the three eagles that was soaring above the one perched in the tree:


I've heard a lot about the bald eagle nest surveys that have been conducted in the San Juan Islands over the last four decades, but had never actually seen the hard data. I know the eagles were historically numerous here, but experienced the population crash all bald eagles in the lower 48 did when DDT became such a problem and the species was listed as endangered. After protection, both the national and local population recovered, and bald eagle recovery was such a success story that they were delisted from the Endangered Species Act in June of 2007. I had heard that more recent surveys revealed 100-200 active nests in San Juan County, but that's a pretty broad range so I decided to investigate a little further.

A little web search turned up the WDFW Washington State Status Report for the Bald Eagle that was published in 2001. Scanning through it for information pertitent to the San Juans, I uncovered some interesting facts backed by published data.

Most of the early Washington eagle nest surveys focused on the San Juan Islands, and aerial nest surveys were conducted from 1962-1980. The 1962 survey monitored only 5 nests, though its unclear whether or not these were all the nests they could locate or just the ones they chose to watch. The peak number of nests monitored was 60 in 1978. In 1980, the Washington Department of Fish and Wildlife (WDFW) intiated statewide eagle nest surveys. The last survey they provide information on in this report was conducted in 1995. At this time, there were 817 eagle nests in Washington State, 102 of which were in San Juan County. Compare this to the 1950s, when there were only 412 nesting pairs in the lower 48.

A few other studies focused specifically on eagles in San Juan County. They found that in the county, active nests occur within an average of 4-5 miles of each other, something people often ask about. In a prey analysis at 67 nests in the San Juans and Puget Sound, they found that 67% of prey items were birds. This surprises me, as I thought they would mostly be feeding on fish, the prey item that comes in second at 19%. The list is finished out with 6.8% mollusks and crustaceans (!!!) and only 6% mammals.

Its cool to find some more concrete information on the local eagle population. They must still be doing some type of population monitoring, so I'll be on the look out for anything more up-to-date. In the meantime, I'll let you know if I see any golden eagles!

2 comments:

Jason said...

Monika, great shots of the Eagles. Good info as well. I just made a small post and linked to you so people can enjoy the info and images. It was fun even though we did not see Golden Eagles. Let me know when you want to do some woodland birding?

NW Nature Nut said...

Love your Eagle photos. Glad you will be joing the GBC of February. The birdcam I have is a motion activated digital camera made by Wingscapes. You can check them out at wingscapes.com. Good luck with your count!