First off let me state that I am not a degree carryin' wildlife biologist, merely a trapper and farmer. We all know that most muskrat populations are declining or in some cases disappearing completely.
Pictured is a swamp called by the locals the Nursery Swamp. Pictures were taken facing north. It encompasses about 65 acres. It is a deep basin carved out by glaciers and silted full over the years to a depth of many feet. My grandfather always wanted to excavate it to look for mammoth or mastodon bones. Back in the 1950's, and before, it was used as cow pasture by its 2 owners, Ralph Space (my grandfather) and Bill Van, a dairy farmer. I now own Bill Van's portion, my brother owns Ralph Space's portion.
In 1961 my father and his friend Joe Taylor released a pair of beaver into the swamp and they dammed the exit on the north end. There have been at least a few beaver in here ever since. About 30 years ago one enterprising group of beaver dammed the swamp from side to side all the way across the middle in an east/west direction. The dam still exists, made and repaired with mud, cattails and phragmites (frags for short).
Two streams enter this swamp, one from the south end and one from the northwest. Water from the south side stream flows toward this middle dam, eventually finding its way through to mix with the water from the northwest stream and then exit the swamp through the north dam.
From the mid 1960's until the late 1970's I would trap 500 to 800 rats a year in this swamp. You could stand on the hilltop where I took the pictures and see hundreds of muskrat houses. By 1990 there were very few.
Until the late 70's cornfields in both of the drainages for these two streams were weeded using a cultivator. I spent many hours cultivating corn in the Space family fields. In the late 1970's farms around here started to spray the cornfields for weeds. This continued in the south stream drainage until my father quit planting corn about 15 years ago as the bears ate more than he harvested. Since he stopped planting corn there are no cornfields anywhere in the south stream drainage. There are still cornfields in the northwest stream's drainage.
In the last few years I have noticed an increasing number (17 that I could see from the hilltop when the snow was on them) of muskrat houses in the south end of the swamp, but in the northern part of the swamp there are still none. Frags and cattails are about equally distributed between north and south swamp sections. Predators, be they winged or four legged, are equal in both sections of the swamp. The only conclusion that I can reach is that the decreased amount of herbicide coming into the south end has led to the muskrat resurgence in that section.
On a lark, Friday March 14 I set 3 colony traps in the north section where the stream enters and 3 colony traps in the south end where the stream enters. Sets were as similar locations as I could find, none were in runs or at houses. Our season ended the next day March 15 and the 3 traps in the north yielded 2 muskrats while the 3 traps in the south yielded 16.
I already can not wait to see what I find next winter.
First picture is an overall view, second is a closer look at the north end.

Interesting, is the Herbicide the only input that changed?

Very interesting and good work.
Thanks for sharing.

Thank you for sharing your investigation.
A couple of questions
1. Are there still beaver there and are they in both sections?
2. How has the water fall numbers fared over time?
3. are water levels similar to depths of the 60s and 70s?
4. Were there any fragmities in either marsh during the 60s and 70s?

Bryce

The north end does have a lot of trees around it. I don't do well around trees due to Hawks and Owls.....just another thought.

Fertilizer has been named as culprit before as well. What’s aquatic veg/food look like?

As far as I know: yes

Still beaver there, the lodge moves from 1 section of the swamp to another every few years.
Water about the same as the 60's and 70's, some years it may be a few inches deeper than others, never goes dry in the summer. Frags started to show up there in the 1970's. No more than half of either side is frags, lots of cattails in both sections. All the rats I caught were fat as fall coons.
You can not walk across this place, it is a sinkhole. In the 1950's we put 25 horses in the Space owned side and only got 20 back out 5 sank in the mud and were gone. Several guys almost drowned in there hunting ducks in the 1960's. Had to use a rope fast to a tractor to pull one guy out of the mud.

Trees are all around all sides about equal.

Fertilizer used on all cornfields and hay fields in both drainages is cow manure.

Do you think the fertilizer was making the environment undesirable or unlivable?

This is an interesting topic. Thanks for info.

Herbicides and insecticides are poisons and their over or improper use causing buildup in the environment can’t possible be a good thing. Causing devastating consequences as DDT taught us. Mutated frogs and lowered fertility of aquatic animals have been linked to them. We are just seeing the effects of the new “safe” notices being used. We need to work hard at being caucious using them as possible.

Interesting ! Golden triangle in Mt is big time chem fallow area .Parts of it seem to me DEAD ,absence of sounds (birds etc ).I am a farmer not a kook ,too much of anything is not good .

It would be interesting to know what the ph is in each end.

I think Buzz said one time he did research project on residual atrazine in streams, in college.

People spraying crops can be poisoned with over exposure. Triazine poisoning is one that i remember currently.

Would rats figure out that the water is bad in one end and they need to stay out? If it's spray related I kinda doubt it.

Do the rats that migrate back and forth figure that out?

Do the rats that migrate across and stay, get sick and die before they winter over?

Eric, your observations make more sense that dozens of studies that had no firm conclusions on the decline of muskrat populations.

I think you are absolutely right Eric. Been saying it for years. Personalty, I think it effects the standing water, swamps, ponds, ect where there is little water flow. Those herbicides lay in that slow water, as opposed to the faster moving creeks and rivers. But, then again, the plant life around the slow water doesn't seem affected. I know, in certain rivers and streams, my conibears will rust up something fierce after a few days, like they have been sitting in vinegar. Seems the water has a high alkaline or Ph to it. I don't know.

See you at the auction this weekend.

Very interesting. Thanks for sharing.

Probably several reasons muskrats disappearing, Ours is mostly gone, but no agriculture to speak of, but a lot of runoff from lawns, and street drains, who knows what's in that ....

Frog mutations have been "linked" to herbicides and pesticides. But correlation does not equal causation. Frog mutations such as the development of extra limbs has been proven to be caused by a trematode parasite, specifically Ribeiroia ondatrae.
I do share your concerns about proper use of pesticides/herbicides, but misinformation about deformed frogs will not help that cause.