I have seen birds of many different species poke their own chests with their bills. Even if they are not doing it, one can practically see the parting of feathers at the spot where they do it. To illustrate my meaning I will post a few photos I got of birds doing this. Why do they do it?
Preening! A bird’s feathers need to be oiled, re-zipped, picked through for tick, mites, lice, etc. and generally cared for. If a bird doesn’t care for its feathers frequently, it can’t fly as well, can’t thermoregulate as well, can’t impress mates and rivals, is prone to disease, and so on. Watch birds longer, you’ll see them jamming their bills into pretty much every part of their bodies.
Edit: I said this literally at the exact same time as the first comment. The fact that it shows up after looks a bit like I am questioning the above statement. As in, “preening? I dunno 'bout that”. But I do know 'bout that. And that’s why I said “preening?”. Just for some context that nobody asked for.
Side-note: ever noticed how some birds (e.g. sparrows) would sweep their beaks on a branch - in quick succession, sweep from the left, then sweep from the right, then again - like a paintbrush?
like everyone else said, yes, preening! My pet quail can stretch and preen their necks too. I have seen other birds do that and it looks really odd on first glance. They will often go to an oil gland on their lower back too, watch for that.
Is the gland for preen oiling at the tip of the collar bone? Is that why they all poke that specific spot? It’s as though they get a bit of lotion, spread it, then get some more.
The preen gland is at the base of the tail feathers, about where the rump patch is on a Yellow-rumped Warbler. Most birds have an apterium, a patch of skin where no feathers grow, on their chest. The feathers growing on either side of this apterium have to be carefully maintained to cover it or they will lose a lot of heat and look very messy. The bare skin may also be a popular gather spot for some parasites, I’m not sure. And when your bill is cold the apterium probably is an easy place to warm it up. That said, after decades of watching birds, I’m not convinced that a bird spends more time with its bill in its chest feathers than in its shoulder feathers or other convenient locations.
This sounds like the answer I was looking for because it would explain the white mark I see on the blue jay in my photo above. I have noticed this pattern of feathers in numerous birds and wondered about it–whether the patch is bare from all the poking. But why poke in the first place? I like your observations and suggestions. Thank you.
