They could be adjusting their crop. I have some chickens do this more than others. Or just yawning. I wouldn't worry unless they are obviously acting sick.Blue and Charlie have both been opening their mouths wide and making a bit of a retching movement in their throat.
I have a favorelle who regularly gets what looks & sounds like hiccups. Incredibly weird but despite me freaking out the first couple of times it happened it is perfectly normal for her. She's my only chicken that does it too.

I feel silly now ....






