Our fourth lesson is about RTHU wings. Now we’re going to get a bit more technical and split hairs, or more precisely, split feathers.
Having been lucky enough to spend nine days as a “citizen scientist” trapping, studying and releasing RTHUs in their Costa Rican wintering grounds with an expert naturalist, I can tell you the experienced eye of a professional determines the gender of the bird by examining the tips of its wing feathers! Amazing!
It’s impossible to study this bird’s wing feather tips, of course. But if I explain the variation we can apply what we know to this picture to see if we can guess.
When the experienced naturalist spreads the RTHU’s wing feathers, s/he can observe the feather tips. S/he looks for the #6 primary feather and observes if it is sharply pointed or rounded. Male RTHUs have sharply pointed #6 primary wing feathers. The female RTHU’s corresponding #6 is rounded.
Okay, student bird spies. Take as close a look as you can and see if you can tell if the 6th feather (from the top of the wing) is pointed or rounded. (Heck, it’s a challenge just to figure out which feather is #6!) Yes, it’s just a guess on our part now as we can’t hold the bird to spread and examine its wing feather tips.
We’ll wrap it up with Lesson 5.