Well crossed fingers that dice rolls and statistics won't play a part in this. Since we aren't aware how acutely aware they are of their surroundings yet. All of them could have been solely focused on attacking that one bird. So if the sing does fail, maybe that also spares them from noticing another target to rush. Since Sing ‎is normally a 50/50 ordeal (55% in games to be specific) and if it is distributed individually, means some may fall asleep and others might immediately now know something is up and start trying to locate and frenzy attack the source. (Though they're huddled up together so maybe 'luck' could consider that as a group...) 

I'd say it was a good action in IC. As it makes sense for a moral character to try to stop another innocent being from getting hurt. But in OC, it feels like a Leeroy Jenkins moment where a character aggro's an aggressive party of monsters when the rest of the party isn't prepared for it. :P