Dante and Randal usually only beard for one of two reasons:
1 - They're scared or angry
Randal hates it when Dante is around him, so he beards up at him. Dante hates being outside, so he'll beard up then.
2 - They're just stretching
I've seen them both do this in the morning (their morning stretches :lol: ) and sometimes in the afternoon, and also when they're trying to shed.