I've caught two beaver out of one colony and both castor sacks were nearly empty, and the oil sacs were tiny. They were both smallish, probably 1 1/2-2 years old, but still plenty big enough to have castor. I was wondering if the castors were just deflating, but I caught a pretty good sized beaver out of a different colony today and he had a good amount of castor. So is there something genetic that could be going on that beaver out of a specific colony will just naturally have larger, or in this case small castor? I hope I'll catch at least one or two more tonight to see how full theirs are.

Age, sex, and time of year are the real factors. Can't see where location of the colony makes much of a difference.

"Smallish" meaning sub adults will have mainly empty hulls. Two year old and adults will have fuller castors.

Breeding males tend to have the largest size.


Different age males.

Sub adult castors are on the far left.