Sunday, July 13, 2008

Clark's versus Western Grebe

The road through the Bear River NWR.

On our daylong field trip to Bear River NWR in Utah, during the recent American Birding Association convention, we got to see large numbers of both western and Clark's grebes. This was a real treat for me. I'd seen lakefuls of western grebes before (in North Dakota) but picking out the very few Clark's grebes in those instances was always like a game of Where's Waldo. Here at Bear River it was more evenly blended between the two species.

Big western-type grebes look black above white below from a distance.

Just like house finch versus purple finch or sharpie versus Cooper's hawk, telling these two very similar grebes apart seems quite tough at first. But given a chance like we had to study the birds well under perfect viewing conditions, the differences between the two grebes become more obvious.

Western grebes.

Both are large, long-necked birds that appear all-dark above and bright white below. The key field marks to look for are all on the head. Start with the face and look at the area surrounding the birds' bright red eyes. See how the western grebes look darker headed with the dark "cap" actually encircling the eyes?

Now look at the Clark's grebes. Notice how white-faced they look? And the white (not black) encircles the eyes.

Clark's grebes.

Another good head-based field mark is the difference in the bills of the two species. Westerns have a yellow-green bill that looks fairly stout and substantial. By comparison the Clark's bill is bright candy-corn yellow and much thinner.

Looking at my two images of these mated pairs of grebes the Clark's grebes look daintier to me: Their eyes even look smaller. The western grebes on the other hand look chunky and dark-headed, and big-eyed.

While we were watching these grebes feed and squabble and court in the ponds at Antelope Island, I noticed that at a great distance I could make fairly accurate guesses about which species I was seeing. If the birds looked more white than dark they were usually Clark's. If they looked more dark than light, they were westerns.

Next post: Doing the Splashy Dance

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