Undertail Patterns – Useful for ID

I’m basically a generalist. There are few things which I want to become an “expert”. When it comes to birding I want to know the key points, including status and distribution, to be able to positively ID a species. But I don’t spend hours going over molt and plumage. One of the things I do periodically review to help ID species is undertail patterns, especially on Warblers.

Last Saturday I met up with Mike and we basically caught up on the week because there weren’t any migrants moving at the local park. Just quiet. As were my next couple of stops. I made a final quick stop at Atterbury before the rains of the afternoon hit. The last two weeks Mike and I had commented on not hearing Indigo Buntings for some time.

My first sighting of an Indigo Bunting in over 3 weeks. Even in the rain the ID is pretty straightforward. Unlike the next species. Atterbury FWA 8/27/16

As the rain started in earnest I was getting back in the car when a small yellow bird went flying into a nearby tree.

I initially thought from the size and coloring it was a Yellow Warbler since they breed in good numbers in this area. But the eye seemed a little too big. Could it be a Wilson’s Warbler?

This is where Undertail Patterns come into play

WIWA (1)
From this view I’m still not sure of the species. Atterbury FWA 8/27/16

I first came across the importance of Undertail Patterns in Jon Dunn and Kimball Garrett’s Warblers field guide. The drawings show how a warbler would look from beneath a warbler.

Undertail Patterns A
Note the Undertail Patterns of the Yellow Warbler, upper left block, and the Wilson’s Warbler, lower right block. Plates 31 and 32 from Warblers.

Since I didn’t get a definite view in flight or initially on the limb, if I could get a good view of the Undertail Patterns of the bird I could probably confirm the species.

WIWA (4)

WIWA Undertail Patterns
The original and cropped/enlarged photo showing the dark undertail pattern of Wilson’s Warbler. And if you look close you might see a smudge of dark on the crown.

So knowing your Undertail Patterns can be useful in ID’ing certain species.

Note: If you look immediately left of the Wilson’s Warbler Undertail pattern in the plates above you will see Hooded Warblers have an all white pattern. I still don’t know why I didn’t know that