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#53887 - 05/31/01 08:40 AM Bear litters
trappnman Offline
Predator Master

Registered: 04/21/01
Posts: 54
Loc: Lake City, MN
In some previous posts, the size of litters vs. density was discussed. It was pretty much proven that the two are not related, or at best distantly. I asked my cousin, who is "the bear man" in Wis. and here are his thoughts regarding litter size in bears- seems to "bear" out the same conclusion.


Litter size is related to: age of sow and how good the previous fall was.
When there are plenty of acorns and fall foods available and they can put on
the fat,they'll generally have average litters (about 3). Their litter size
though can be anywhere from 1 to 6.
Generally sows don't breed until they're 3 1/2 ,but I'm finding them breeding at 2 1/2. These young moms usually have only one or two cubs and the survival on them is low. Seems like when they leave the den , they
fall to predation. Mom doesn't seem to know what to do and she gets intimidated
real easy by the boar,which kills the cubs.
Density can have an impact on litter size, but we haven't seen that in either Wisc. or Minn.
Mike Gappa
Wildlife Biologist
West Central Region- Eau Claire
(715) 839-3774

------------------
Your American Heritage- Fur Trapping, Hunting and Fishing

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#53888 - 05/31/01 08:44 PM Re: Bear litters
steve allen Offline
Predator Master

Registered: 01/05/02
Posts: 88
Loc: Bismarck,ND
Trappnman--Nice input on bears! Fasinating? I know zilch re: bears; however, I could do some literature searches and come up with something. Looks like you have already done the recon work. Nicely done! There are a couple of guys that post on the lions/bears forum that will certainly be interested in this. Hope they see it.

I was especially interested in the observations indicating age related increases in reproductive performance in bears. A couple of questions for your cousin if you don't mind. Are bears monovular; that is, does each ova potentially produce 1 cub or are bears polyovular? Also does ovulation rate increase with female age class (like the canids) up to say 5 or 6 years? What happens to prenatal mortality rates with increasing age; do they decline? Just curious for my own understanding.

Again, thanks for posting this info!

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#53889 - 06/04/01 05:13 PM Re: Bear litters
trappnman Offline
Predator Master

Registered: 04/21/01
Posts: 54
Loc: Lake City, MN
Here is Mike's answer concerning your questions Steve:
Breeding occurs anytime from late May to mid August ,with the peak
being
around the 4th of July.Black bears have a seasonally constant estrus
.They
remain in estrus until bred or until the ovarian follicles begin to
degenerate.Ovulation happens as a result of stimulation.
The gestation period is 7 to 8 months,however most development takes
place
during the last 6 to 8 weeks ( basically when the sow goes down for the
winter). Bears have whats called delayed implantation (similiar to
mustilids). The blastocysts float free in the uterus and do not implant
until Nov. Only minimal cell differentiation takes place prior to
implantation.
Cubs are born at this latitude around mid to early Jan.

The only thing I can say about ovulation rates is that from what
I've
seen,generally the young sows(first time breeders that are 2 1/2 yrs
old)
generally have one cub.Very old sows generally have one or two
cubs.Everything in between can have anything from one to six.Again,it
seems
that when we have a fall with very abundant foods that recruitment is
high.
Which makes me believe that conditioning the animal in the fall has
alot to
do with litter size.

Which brings us to pre-natal mortality. I'm sure it happens in the
years
where the animal enters the den in poor physical condition. I don't
think
age is as big a factor as condition of the animal. I've done some old
sows(greater than 15 yrs. old) that have had normal litters and I've
done
some sows in their prime (5 to 7 yrs) and they've only had one.Again,I
think
pre-natal mortality is more of a function of the condition of the
animal
than age.

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#53890 - 06/04/01 05:59 PM Re: Bear litters
steve allen Offline
Predator Master

Registered: 01/05/02
Posts: 88
Loc: Bismarck,ND
Trappnman--That is some really nice information you posted. I understand exactly what you are saying. My compliments to you and your cousin for providing it to the readers.

Now a couple of more questions, if you don't mind. Do all bear species have similar patterns of reproductive performance? Has your cousin done any population modelling on black bears? What does he see for annual turnover rates and harvest rates within the turnover rates that will maintain stable populations? Again I'm not trying to pin anyone down, but just trying to increase my understanding and that of other readers of a species that many of us know very little about.

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#53891 - 06/05/01 08:39 AM Re: Bear litters
trappnman Offline
Predator Master

Registered: 04/21/01
Posts: 54
Loc: Lake City, MN
All bears have a similiar pattern when it comes to reproductive performance.It will vary somewhat between species(there's 8 differnt species of bears in the world).For example, the sow black bear keeps her cubs
for about 16 months before she kicks them out. The brown bear keeps her cubs for
28 months before she kicks them out. The concept is the same and only differs through time intervals.All bears have delayed
implantation, gestation periods are about the same,but time at first breeding and intervals between breeding may be different. Again,the concept is the same.
Yes I've done modeling work.Right now I'd say Wisc.'s population is growing slightly in some areas of the state and remaining stable in some other parts of the state and on a slight decline in the other
zones..Statewide I'm looking at a harvest rate of about 22%. That should at
least stablize the population if not make it decline a little. Repro. is keeping up with harvest Our objective here in Wisc.,like Minn., is to decrease the pop. Our
goal is to have 10,900 bears and currently we have 13,000+.The problem is that
in some parts of the state we have more bears than we'd like,in other parts we
don't have enough and in other zones we have the right amt. For us to decrease #'s,we have to target the zones that have more bears and increase the harvest % to 25% of the pop. in that zone.Of course when you do
that, you increase competition between user groups and the the quality of the hunt goes down and problems start happening.
Mike Gappa

------------------
Your American Heritage- Fur Trapping, Hunting and Fishing

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#53892 - 06/05/01 12:26 PM Re: Bear litters
steve allen Offline
Predator Master

Registered: 01/05/02
Posts: 88
Loc: Bismarck,ND
Trappnman/Mike G.--Thanks for the info re: bears. That is very interesting at least to me. I was unaware there were only 8 bear species in the world. Very interesting data on populations, too.

I fully understand the problem of achieving population objectives in different regions and the bellyachin that can sometimes accompany management decisions. Been there; done that! Nevertheless, it needs to be done.

Thanks again!

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#53893 - 06/05/01 07:47 PM Re: Bear litters
steve allen Offline
Predator Master

Registered: 01/05/02
Posts: 88
Loc: Bismarck,ND
Trappnman/Mike G.--Another question after re-reading your posts. How do you measure condition? When we looked at coyote reproductive performance and other things in North Dakota we had no choice but to measure relative depot fat levels, because all our animals were dead--sometimes for several days. Is there new technology available that utilizes samples from dead animals to determine condition accurately? Now I'm really curious.

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