There is always some question about when beaver birth their young. I opened up a female (big nippled) today just to see. I have seen them a lot bigger. These, and I didn't weigh them, but I figure 10-12 onces apiece and there were only 2 inside here, which seemed odd.

On pics either, I could take one but they are sort of graphic, and the last time I did that they got axed.

I will say that I've seen the fetuses a lot bigger than this, and I believe she was 2 or 3 weeks away from having young, which is in keeping with the "late May , early June" timing I have heard spoken of on this forum before.

Old subject , but I thought I would regurgitate it again. I am up on the Canadian border, to keep things in perspective.

What makes only having 2 seem odd?

First week of june is avg normal here Les.I have opened quite a few doing the nuisance beaver work.The females will sometimes have a late litter(late june,july) if the male was trapped in the winter.The beaver normally mate in Feb under the ice if you back track the gestation time from the normal birthing week.A female will mate late if they find a male after an early ice out in march.This is evident when you catch those extra small kitts in the fall.

Very interesting guys, thanks for the info. Which get larger overall male or female?

Osky

As far as I know,Osky beaver continue to grow their entire life.The longer a beaver lives the bigger he gets.I don't know which get bigger at the same age,male or female.I have caught some very large beaver on occasion of both sexes.On avg our beaver don't get as big as I see some on here from out west and in parts of the states.I believe it is because ours don't survive as long as beaver in a more favorable environment.

Thanks Boco, I with my limited beaver experience could not see a size differential.
It came to mind as the other evening I was slow running the boat along the shore after doing a bit of beaver work and had one out and swimming parallel at about 12 feet out that was far and away larger than any I could even imagine, including those I've seen here. The head was massive and the body unbelievable. Went side by side for nearly 100 yards and I was wondering what sex such a freak would be.

Osky

I caught a 80Lb female In May. When I opened her up I found 10 fetuses. I think maybe 2 would have been born the rest were very small and I doubt weather they would have been born. I took that beaver and the fetuses to the UW of Wisconsin Madison. They had witnessed 8 but never 10. Never weighed any of them.
I got the hide back and sold It.

I have a pond that is have caught 7 yearlings for two years straight

I am 90+% sure there is only one large female there as after catching her young of the year as well as her mate for 4 years straight and then nothing, I'm confident she has birthed all seven each year

Had one that raised 10 a year for 2 years.Took her in the fall of the 3rd year,she weighed 86 pounds.
In areas I trap,most raise an average of 4 a year.Usually if the number is under 4 ,it is a female with her first litter.Older larger beaver will many times raise 6 or 7.
Tom

I have never caught more than 4 little ones, per lactating female, at a location that I was certain how many lactating females were there.

Most of ours are born the first two weeks in March.

When ever I caught more than 4 small beaver, I always caught another lactating female.

I believe climate is a big factor.

Either sex can be bigger, not like most other species. And I think 8-10 is a pretty uncommon. I think 3-5 is the common amount of little ones.

I haven't opened up that many, but 4 is common to catch per lactating female, or in any size class. I have caught 5 in the same size class in a colony .

I have a pic in my files, the one I've showed here before of A female opened up, with 8 fetuses .

If I open up more first year females , I may encounter more litters of less than 4, I suppose.

3 to 5 for sure is the norm here.A lot of beaver don't make it past the first fall of the year.And a lot that do don't make it thru the second.Predators like lynx,fisher,wolves and foxes make short work of them once they start venturing near shore and on land in the fall putting up feed.Once they get to a larger size they have a much better chance of escaping a predator attack.

I think survival is better here. If I wipe out a colony, there are rarely any numbers missing, that I can tell. 4 , 4, and 2, with an odd old beaver here or there in a full colony is the norm. Almost as if the predator base is down.