Friday, August 21, 2015

Fri-D: Drilling Down to an I.D.

Hmmmm, you look like an Olive-sided Flycatcher.
That's how it started with the bird in the photo above. The bird is dead center in the frame if you have a hard time seeing it. This is an uncropped image, taken Sunday, August 16, 2015 at Cape May Point State Park, NJ.  If you figure that I was using a 300 mm lens with a 1.4x teleconverter on a cropped frame sensor (DX in Nikon terminology, adds a 1.5X multiplier), then in 35mm terms that's 630mm worth of lens.  If you use the old rule of thumb that you can estimate magnification by dividing lens length by 50mm, then this is the view you would get through 12X binoculars.
The math looks like this: 300mm X 1.4 X 1.5 /50 = 12.6
I was using my customary Zeiss 8X42's, so what I saw in my binoculars looked substantially smaller than this. But it still looked like an Olive-sided Flycatcher.  I knew this in part because I've seen a lot of Olive-sided Flycatchers (though they are a scarce to rare migrant in the east), and in part because it was August 16 and I had been thinking about OSFL all morning, and wanted to find one.  I wanted this bird to BE one, which is a very dangerous thing in bird i.d. If you want to find it, you will - even if you're wrong.
But supposing you came at this bird without pre-conceived notions.  Then what?  Well, for starters, a lot of bird identification is about what it is not. This is not a goose, swan duck, turkey, loon, grebe, shearwater, gannet, cormorant, pelican. . . you get the idea. . .then you get to some things that it could be, like a dove, cuckoo, flycatcher (ding ding ding!), jay, swallow, thrush, warbler, sparrow, finch.
It's smallish but not super small.
Then you can consider where you are, and where the bird is.  We're in Cape May, it's August 16, and the bird is perched on a prominent bare snag. It is not interested in leaving that area, as I learned by watching it for quite a while. It is perched in a fairly upright position. Now what are the possibilities?
Purple Martin. Red-winged Blackbird. European Starling. Or some kind of flycatcher.
The first thing I did was get down on my knees and prop the Zeiss on the railing of the observation deck, thus creating a very stable image.  It can be amazing what you can see through mere binoculars when you do this.  I was getting no color at all, just a silhouette, but I got a clearer picture of the bird's shape - upright, big-headed looking. At first I couldn't see its tail because of the way it was perched.  Then it preened briefly, holding its wing out to the side, and I could see it had looong wings, and for an instant thought to myself, "You dolt! Are you just looking at a Purple Martin?" But, even without a look at the tail, the shape was wrong for that. And long wings are just fine for OSFL.
Then the bird shifted position:
 You can click to enlarge these images, by the way.  Now I could see it had too much tail for a martin, the shape still seemed great for a flycatcher, and specifically an Olive-sided Flycatcher.  Then. . . waaaiit a minute, am I seeing white tufts on this bird's butt?  Why yes, I believe I am.

Then I cheated.  I looked at the back of the camera, and zoomed in on the bird as tightly as I could. This is what I saw:

 Olive-sided Flycatcher.

Here's a bonus challenge, if you're in the mood.  Yes, I know the camera's autofocus somehow decided the ripples on the water were more important than the totally obvious birds (grrrr), and the light is bad, but sometimes this is how we see things through binoculars.  And, you can study these at leisure, unlike conditions in the field.

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