The first thing to realize is that this picture does not show what it appears to show.
It is easy to imagine that this is a picture of a bird squatting to poop in a field. That is not what is going on, but what is this Great Blue Heron doing? In a few decades of casual heron watching, this is only the second time I have seen a heron adopt this stance — it is far from being an everyday sighting. My first sighting, in the summer of 2012, was posted with a detailed discussion as balalaika heron.
Ok, the executive summary is that the heron is baking its parasites. The underwing feathers become infested with parasites, but they cannot withstand high temperatures. By exposing them to sunlight and so heating the underside of its wings, it kills and so rids itself of parasites.
It was in the heat of summer on the earlier time I saw a heron doing this. The heron had to go to a great effort to prevent the heated blood from reaching its brain by extending its neck. On this occasion, the air temperature is only about 5 °C and the heron’s neck is not extended, but the result is the same: feathers cleared of parasites.
A Great Blue Heron bakes its parasites by spreading its wings and exposing them to sunlight.
This is amazing. How did you learn that the squatting was related to parasites?
Birthe, the heron is not actually squatting — it merely looks that way to human eyes. It is just standing there. What looks like knees are bends in its spread wings. As to how I learned what it is doing, that was explained in the earlier posting, balalaika heron. I had sent the picture to a heron expert, Rob Butler, and he explained it to me.
This delta wing pose has always puzzled me. If it is parasites in the wings then why not hold them straight out to maximize the feathers getting direct sunlight? In this photo it seems the bird is not even directly facing the sun.
In your first post, the bird seems to be reflecting sunlight into its breast and belly area. Reminds me of someone using one of those foil tanning reflectors. We are going to have to learn how to speak heronese.
Max, about speaking heronese, you will notice that in the first posting I said that: “in my experience, herons ignore even polite informational requests.” I too have wondered about the details of the stance. My guess is that it is just the inside underwings, wing pits, and adjacent breast regions that normally are hospitable to parasites, because that is where they are generally sheltered and moist. With this insight, the stance begins to make sense.