Yes, hens will chase/catch/eat whatever mouse, bird etc is within the vicinity. And if one bird has a mouse in it's beak, the others will frantically chase it and pinch it - then that bird gets chased etc etc.....
My birds free range and they will chase off my cats if they are in the mood to, for no apparent reason. It's a chicken thing but just bear this in mind if you have any poorly or old animal who might be a bit slow for any reason.
Also, if a bird in the hen house is injured for any reason, the others will go for it and peck at the bloody area, so separate the injured bird.
Hope this helps.