Oh yeah, I had a pullet that used to burp while she was drinking. I watched her as she was taking a drink and she was swallowing air every time she swallowed. So right after the water went down, she would expel the air and thus a burp!
As she grew up, she learned how to drink with out swallowing so much air. I haven't heard any burping lately.
Chooks burp and 'fart'. Funny critters.
Some will simply swallow air when eating too fast.
As the get older they slow down and it doesn't happen as much.
We have some CCXs and they swallow air all the time because they try to eat fast all the time. TheyreT 10 weeks and still burp and pass gas. Funny girls.