Tuesday, April 15, 2014

Otters and Beavers Share a Winter Pond

Although I began winter tracking in 1994, I didn't get any inkling of how beavers and otters share the same pond until March 1996 when I saw a huge hole in a dam that I thought could only have been made by otters. I saw their prints, slides and scats in the snow all around it.

In the fall of 1997 I saw how a mother otter used beaver ponds to raise her pups, teaching them how to catch fish and live in an ever expanding range encompassing the ponds of several beaver families. Then for most of 1998 it seemed as if my schooling by otters ended. I tracked otters from pond to pond in January and otters seemed to make themselves at home just behind the same dam they breached the year before, but they didn't breach it again and soon moved on.

In 1997 I saw otters on 15 different days, usually up to a half hour at a sitting. I only saw them 5 times in 1998. The beavers seemed as active as usual both years. Their main lodge in what I soon called Otter Hole Pond grew larger even though the beavers spent a good bit of time in the pond just below it. The water of that lower pond which I called Beaver Point Pond lapped up to the downstream side of Otter Hole dam. 

In late November 1998, I saw 4 beavers out in the pond working on and around the lodge, preparing it for winter. 

I noticed an increase of otter scats around the ponds in December, and some possible otter slides on the pond ice. There was no snow on the ice making it hard to see otter slides but easy to see how the ice of each pond brimmed the tops of the dams holding back more water than I had ever seen in those ponds. 

As is often the case on the island, winter struck hard on New Year's Day as the high temperature hovered around 0F. Beavers react to the bitter cold by hunkering down in their lodge after a long autumn of overeating. You seldom even hear beavers in their lodge unless the temperature is 20F much less see them up on the ice. But I've tracked otters for miles when it's 0F. 

We had snowfall and, of course, it became easy to see where the otters were active. I saw otter slides going from granite boulders where I knew they liked to den heading straight to the beaver lodge.

That same day, January 5, I saw that there were cracks in the ice,

The ice of the beaver pond was buckling as it collapsed behind the dam.

I've learned in the years since that beavers also breach their dams in the winter but I had no doubt that the otters made that hole in the dam in early January 1999. When I looked up at the dam from the pond below, I could see an otter slide from the dam to a pool of open water in the ice below that the water flowing through the hole in the dam created.

Soon there were holes in the ice behind the dam along the shore of Otter Hole Pond. I saw fresh otter scats around the holes on January 5, 6, 7, 12 (with 3 fish heads), 17, 20 (with fish entrails), 21, 22, 25 (with 5 fish head including one of a grass pickerel).

It wasn't easy keeping track of this. We had five more inches of snow; then freezing rain; then rain; then more cold. Then after a night bottoming out at -18F, we had a foot of snow bringing our snow pack to 22 inches, with much of the lower strata rather icy. On the 18th we had a thaw accompanied by heavy rains. I expected to see that the beavers in Otter Hole Pond had come out to forage for bark, but they didn't. I did hear mewing in their lodge.

I usually checked the ponds in the afternoon when it's warmer. But in late January the temperatures were consistently warmer night and day so on the morning of the 27th I went out at dawn determined to see the otters.

I had a ringside seat atop the granite rocks where they had their den. I heard some cracks of ice - thumps really and got the feeling that somebody was there, but ice does crack as the morning warms up. Well, I did not have to wait long. I heard noise below me and then an otter came out. I had a good view as it squirmed in the snow stretching for all it was worth.

Then it got up and rather directly centered its behind over the previous day's scats and let fly. Tail was out, up, and firm, the rest of the body did a rhumba and twitch.

At the same time I heard a splash, so there were two otters. I soon saw an otter below me again and again it let fly with a scat and disappeared back into the rocks. Then all was quiet below me and I focused on the hole by the dam. Soon enough there was the sound of cracking ice and then a head popped out from a hole a few yards further down the dam. The otter's head was hard to see

and no action on the ice. I heard chirping, the usual sound otters make to connect with other otters. Then I got the great idea of going on the ice and standing midway between the dam hole and the cliff holes. I heard the beavers mewing in the nearby lodge and I heard otter splashes, I presumed, under the ice. Then I heard snorting right under me. The otter either saw me through the foot thick ice or smelled me. I heard more snorts and then I saw an otter head poke up out of a hole near the cliff, snorting right at me.

I made believe that it didn't see me. The otter ducked, soon swam under me and snorted at me again. It wanted me out of there. So I left.

As for the beavers mewing in the nearby lodge, I was not as great an interpreter of beaver mewing as I was of otter snorts. However, I had never and have never heard otters make sounds like beavers. When I've seen beavers stressed by otters, I never heard them make a sound -- they slapped their tails. When beavers have been stressed by my presence I've heard a huffing but nothing like the growl or screech made by an otter stressed by a beaver or me. All to say, I was pretty confident that the beavers were in the nearby lodge and reacting to my presence and the otters' with apparent equanimity.

It was warm again on February 3. I checked Otter Hole Pond and saw that there was such a large pile of scats at the rock cliff that it was evident that every morning since I last saw the otters they had come out and crapped at that spot. The set-up was so perfect I decided that these otters did not scoot around through the woods to other ponds because they did not need to. The otters seemed to have shaped it just the way they want it. The ice sloping down from the shore afforded two to three feet of air space, a veritable under ice gallery by the shore, and I bet that the way was clear to most of the pond, that big blocks of ice had not collapsed to the bottom of the pond. Meanwhile by the lodge I heard several beavers mewing, harmonizing.

No sooner had I decided that the otters would spend the winter in those two ponds, connected by a hole through a dam, then the next time out I saw two otter slides leaving the ponds. I tracked the otters to the ponds in neighboring valleys and the next few times I came to Otter Hole Pond, I heard mewing, moaning, and gnawing in and around the beaver lodge. It was turning out to be a warm winter. Perhaps that's why the otters became so rambunctious and moved.

But they certainly didn't forget Otter Hole Pond. On February 11 at least one otter was back in the pond. I saw a fresh bullhead head on the ice behind the dam, and on the other side of the dam I saw a fresh scat on the with attendant scrapping.

Finally on February 17 I saw a beaver sitting in some open water in Beaver Point Pond gnawing on a branch. For the past two years, I had often seen beavers swimming up Beaver Point Pond and climbing over the dam into Otter Hole Pond so I suspected the beavers used both pond, but I couldn't be sure. Then on the 18th I saw a beaver on Beaver Point Pond as it dived into the water and disappeared under the ice. I walked up to Otter Hole Pond dam keeping an eye on the open water below it. Finally I saw rippling but the beaver never surfaced. I saw the wake on the surface of the water go into the hole and then when I got near the hole the beaver went through and dived into Otter Hole Pond and I soon heard energetic mewing in the lodge. I got down on my belly and could see the light through the hole. So the beavers were taking advantage of the otter hole. 

On February 21 the temperatures turned colder and most of the open holes were iced over. I found that I had perfect conditions for measuring the holes in Otter Hole Pond dam. As I expected all was more or less quiet in the pond. So with a trusty beaver stick with several knobs to help with measuring - and with my 100 feet of tape, I went to work. 

First the big distances. It was 85 feet from the rock cliff holes where the otters denned to the edge of the beavers' lodge. From the edge of the lodge to the hole in the dam it was 64 feet. The two measurements roughly formed a right angle. 

I got on my belly and eased over the new ice and got my stick into the upstream entrance of the hole which I found was about 23 inches wide. At that entrance the water was about 15 inches deep. There was an 8 inch gap, or clearance, between the water level and the crisscrossing logs of the dam. And above those logs was another hole about 17 inches high. I assumed the otters fashioned that upper hole first and then dug deeper. All totaled that was a hell of a hole.

The upper hole I credited entirely to the otters. It was possible the the lower hole, through which the water was flowing as I measured, might have been widened and deepened by the beavers. The depth of the water at the down stream entrance of the hole was 23 inches.

Because the level of Beaver Point Pond is so high, the level of the two ponds had no more than a 3 or 4 inch difference. Beavers commonly breach upper dams when the pond levels equalize. 

I also measured what I call the open space between upper ice level and the water level. At the rocks I measured three galleries 12 inches, 6 inches, and 15 inches. At the dam I measure one at about ten inches of airspace under the ice. 

The galleries were for the convenience of otters when they fished and I saw a fish head on the ice above one. The beavers used the hole through the dam to get down to Beaver Point Pond dam where I saw that they had stripped one large limb and cut down some trees. Plus there was now a major leak in the dam. I didn't hazard a guess as to who fashioned it. I only saw mink tracks there.

As far as I could tell, when the otters came they preferred Otter Hole Pond. They seemed to abandon their rock dens along the shore and I began to find fresh otter scat outside a smaller, older beaver lodge in the pond, about 50 yards up stream from where the beavers were staying. I thought an otter mother and her three pups lived there in the fall of 1997.

I soon noticed that I had a second hole through the dam to measure - 3 feet from top to bottom and a good 18 inches wide. Also there was a hole directly on the top of it, about the size of a football for an animal to slide through. I assumed this was work done when the pond was buried in snow.

One logical explanation for there being two holes through the dam is that if an otter didn't want to encounter a beaver near one hole, it could us the other, or vice versa though in my experience, in beaver ponds otters try to avoid beavers. But having never seen the course of events in any pond shared by otters and beavers repeat itself from one year to the next, I shy away from suggesting there is a logic involved in the unfolding of events.

Usually I clearly saw a mother otter and two or three of her pups. I could tell because I would see one large slide and one set of larger prints accompanied by two or three smaller slides and prints. In the summer of 1998 I saw a mother and one pup in the pond. I heard stressed chirping when I saw the otters in January. The mother feeds her pups most of the summer and when there is only one pup, it stands to reason that by winter it might be almost as big as its mother.

My usual tension while watching otters in the winter was discovering when the mother and pups separated which could occur between mid-January until March, though in the winter 2010 a mother and her two pups were still together in May. The otters I watched in 1999 didn't seem to make a clear separation. In late February I began to think that there was only one otter in the pond. But in mid-March I was once again sure that there were two. 

Otters usually left the beaver ponds in mid-March. The river around the island thaws well before the beaver ponds. Sitting along the river, I've watched seemingly endless schools of perch. Meanwhile those ponds where the dams have been breached are virtually dry in March. Generally when I've tracked otters in the ponds then, I got the sense that they moved from pond to pond searching for deeper water and more fish. In a word, they seemed restless.

On March 14, I saw an otter in Otter Hole Pond. First I saw tracks around a patch of open water near the upper lodge, and a small hole by low rocks on the upper shore.

then I saw a hole deep through the ice and snow next to the lodge the beavers were in.

Three feet down the hole I could see lapping water. There was an otter scat next to the hole. I also heard beavers mewing inside the lodge. Then I went down to Beaver Point Pond dam and saw that at least one otter had been out in the snow there. 

Suddenly I spotted a mink scampering along the shore heading up to Otter Hole Pond. I followed and that much smaller version of an otter darted up and slid down the rocks where the otters had had their den. Then as I was walking away back down to Beaver Point Pond dam, I luckily turned back and looking over Otter Hole Pond dam, I saw an otter stick its head out of the new hole beside the beaver lodge. 

Was it looking for me, again, or the mink, who after all competed with the otter for fish to eat? And what did the beavers think of all this commotion?

This perhaps sounds more provocative than it really was. Beaver lodges might strike us as tight quarters but I have seen one, not as large as the Otter Hole Pond lodge, accommodate a family of beavers and muskrats as well as a family of otters making a brief visit. In that case, I was sure all the animals were actually in the lodge. The otters used a kind of penthouse apartment. 

I was sure that the hole through the ice and snow did not go into the lodge. Indeed the otter probably fashioned it because the only deep water remaining in the pond that might have fish in it were the dredged channels around the underwater entrances to the lodge. That's probably why the mink was interested in the hole too.

The next day the only sign of an otter was at the far upper end of the pond, not near the lodges or dam. Had the beavers enforced some behavior?

But on the next day there were fresh scats, and blood at the hole beside the beaver lodge - beaver's blood? no, bullhead parts.

The otter got its meal just before another cold front roared through. The hole was well frozen. Only the big lower hole at the dam had running water. There were two otter scats there and also a trough made by a beaver. Thanks to a snowfall the day before I could track one otter leaving Otter Hole Pond and going up a ridge and into another beaver pond about a quarter mile away.

The cold and snow in mid March, not uncommon here, finally eased, and the thaw came quickly. The ice on a beaver pond is usually the last vestige of winter, but the thaw raises the water level and there is no more breathing space under the ice. 

Once during a February thaw I saw an otter managing that with no trouble, breaking up through the ice with a fish in its mouth. 

But that year the otters and beavers didn't breach the dam and drain the pond. In March 1999 the thaw resolved itself into a rush of water down the old creek channel flanked by the snow covered bottom of the drained pond.

I kept checking the pond, more to see the beavers begin to address the dam repairs they had to make, and I did see some logs behind the dam and thought beavers might have placed them there by a beaver to brace the planned repair job. 

I no longer walked on the melting pond ice but stayed up on the shores of the ponds and walked out on the dams. It was harder to spot scat. Then on March 26th, as I walked by Otter Hold Pond lodge and heard a crack from the direction of the lodge, I turned to see a head sticking out of the hole next to the lodge. Big enough, I thought, to be an otter, but on the spot I decided it was a mink especially when the beast crawled out along a stick. Then it walked out onto the snow and I saw that it was an otter. A pup who was no longer under its mother's supervision?

It began nosing around the lodge and slowly went behind it - showing its spade shaped tail. A few minutes after that a lump crawled out on the ice below the dam that I thought it must be a muskrat, but soon that picture resolved itself into a small beaver bent over like an old man squinting into the sun, sitting on his tail, sniffing the air, not in my direction. I wished I had a better camera or a closer vantage for how golden was its fur in the setting sun.

Then the otter popped up onto the top of the dam and I don't think looking at the beaver that was swimming complacently in the water below. The otter pranced on top of the dam pausing now and then to stretched its tail up for a scat.

and then it went over the back of the dam and seemed to knock down a loose stick as if it wanted to get onto the business of patching the hole in the dam.

I returned my attention to the beaver and saw how high it floated in the winter - indicating it was young. I couldn't even be sure that it noticed the otter up on the dam, nor that the otter noticed it. But here were too young animals who shared their first winter together under the ice of a pond....

I waited all of April for the beavers to patch Otter Hole Pond dam. When the ice melted around the lodge about 30 of the now stripped logs that the beavers had cached for winter food floated and collected behind the holes in the dam. 

It was as if the pond was repairing itself. But the beavers never stuffed the logs into the holes. Soon a south wind blew them over to the north shore the pond. 

While my wife, 11 year old son, and I saw beavers frequently in both ponds, the only repair work the beavers did was on Beaver Point Pond dam. They built the dam higher and soon they could float effortlessly from one pond to the other.

On April 15, I saw an otter swim through the hole, too. But  it appeared to be on an entirely different mission than it was during the winter. It wasn't looking for lodging and wasn't interested in food or otter pups. As I stood on a mossy cliff about 15 feet up from the pond, it climbed up a rock below me, gained the mossy flat in front of me, and without any hesitation because of my presence, scatted and stomped on the moss doing what a big male otter does at that time of year, mark his territory. 

He then got into the pond, snorted at me, and then swam up through the dam and far up Otter Hole Pond doubtlessly to mark more of his territory.

Seeing that otter made my heart beat faster and it was good to see him roving, not ice bound. Then I settled down to the pleasures of watching beavers, as placid as usual, dining on bark along the pond shore.


Monday, January 27, 2014

Dry Beavers? Porcupines and Survival

For most of my 20 years on Wellesley Island touring the beaver ponds in the winter meant checking on at least four beaver families living under the ice of four large pond. For the last three years, I've had one family in the East Trail Pond to check on. There may still be a beaver or two lurking in the Lost Swamp Pond. Without a family to feed, beavers often don't leave much evidence that you can see proving they are alive and well under the ice.

Meanwhile, just as I have for 20 years, I still see the active dens of porcupines in all the ridges between the ponds. Porcupine dens can be easy to spot in the winter.

Porcupine trails in the snow lead you right to them and sometimes you catch the porcupine not quite safely inside.

For years I've watched both beavers and porcupines and when I saw each animal gnawing trees, I fancied that there had to be a brotherhood of such earnest bark eaters, one felling trees and the other climbing into them, had the same take on life though one was wet and the other dry.

There is a high granite ridge north of a string of ponds that used to host beavers. In the fall, I'd sometimes sit up there to look for beavers, scoping out fresh gnawing near the ponds if I couldn't see a beaver swimming in them. Usually fresh bark stripping by porcupines in the tall trees right in front of me framed the photos of the gnawing below.

The beavers coming out of their lodge in the pond and might go foraging up the slope almost to the rock den where the porcupine lived. The porcupine coming out of its den might climb up the slope and climb the tall trees higher up on the ridge that the beavers can't girdle.

Nice way to split the universe. 

When I joined the porcupine and beaver in brotherhood, it was half tongue and check since I had long celebrated the earth changing virtues of the beavers. No one ever called porcupines a keystone species. 

Then the beavers I watched started moving out and other beavers didn't move in to replace them. The earth changer cycled itself out of the picture. The crown trimmer survived.

It's easy to broaden your view of the comings and goings of animals when you read about it in books. It's another matter when you've become accustomed to watching them and they are gone.

Perhaps by analyzing why the dry beavers, the tree climbers, the porcupines survive so much longer, we can learn something about beavers.

In a nutshell, these seem to be the factors: the porcupine is smaller save for its claws, social in a prickly way and less prolific.

Porcupines sometimes come down to beaver ponds to get a drink and on May 15, 2003, I got a good photo of that.

A wet beaver that size would be considered small. Those porcupine quills are not wet and the skin of the animal is a few inches below the sharp points of the spines.

The lightness of porcupines is better measured when they are high in a tree.

And they always take you higher:

But in a fashion beavers can climb trees.

Once I saw a beaver fall from such a perch but this beaver made a not inelegant dive:

One winter I found clear evidence of a beaver climbing rather high on a half downed red oak still up at about a 20 degree angle.

That's my wife under the tree and she's no midget.

Of course, beavers can't really climb trees because they don't have claws like porcupines.

Once I got a memorable photo of a porcupine climbing a tree showing the cut of its teeth and claws.

Beavers have their own way of getting into the crowns of trees: cut the tree down.

The beaver doesn't have claws like a porcupine, but a porcupine doesn't have jaws like a beaver. And thanks to its much bigger jaws, the beaver's bite is much bigger.

It might be more scientific to share measurements of skulls, but it might be more memorable to share photos of a porcupine likely killed by a fisher and a beaver perhaps killed by a bobcat.

The photo of the beaver skull, fished out of the Deep Pond at my land, doesn't even show the lower jaw, but the gap between the incisors and the molars is considerable. The porcupine's incisors clearly don't have such reach. 

Here are the skulls side by side:

Looking at the massive beaver jaw, it's easy to see why beavers cut down trees. (I hesitate to say that beavers evolved to become tree cutters, because the jaw of the muskrat has the same design. Both are aquatic mammals and I think their jaws primarily designed to bring up and eat the underwater roots and rhizomes of aquatic plants.)

Looking at the jaws of a porcupine it's easy to see that it wouldn't have enough bite to waste time trying to cut down a tree, though it does cut off some branches. It seems designed less for gnawing like the beaver's incisors and more for scraping off bark.

Not that porcupines can't do a number on trees. They have sometimes startled me with the extent of their gnawing, like this completely stripped white oak that I saw on December 31, 2011,

On one very cold day, so cold by camera battery ran out, I stumbled upon a porcupine dining on a pine tree wrapped around the narrow trunk at my eye level. I still had juice in my camcorder and lifted this still from the video I took.

Can't blame that porcupine for getting carried away. But generally porcupines with their smaller teeth gnaw elliptical patches up tree trunks.

Sometimes I see freshly gnawed ellipses next to old ones.

Sometimes I get the impression that a porcupine has bonded with a tree, that it periodically milks it over the years.

Trees can survive such wounds. And in the spring, porcupines feast on the budding twigs and catkins high in the crown.

One fine day in May, I got a video of a bud-obsessed porcupine who seemed to literally put the spring into spring.

Porcupines also commonly sleep high in tree during the day.

I got a video one August of a porcupine waking up as the sun went down conveniently surrounded by thick leaves to munch. Not for nothing is it sometimes hard to see porcupines in the late summer. Why leave that arboreal paradise?

But I hesitate to say that there is some innate sense of conservation in porcupines, that they purposely pattern their foraging to increase a tree's chance of survival. They are simply smaller and have a more modest appetite than a beaver. Trees can usually endure porcupines.

In my experience, only in harsh winter conditions are porcupines likely to girdle a tree.

A valley in some land I own is a hotbed of porcupine activity. Beavers were there for a few years then moved on. So for a period of time, I could fancy I was a tree and ask myself which plant predator I preferred.

Hemlocks are the pride of the valley. Porcupines love them sometimes to death even though they seldom gnaw bark off the trunks. They keep trimming branches until their are no branches left.

I didn't think beavers cared much for hemlocks and thought some small ones cut down were simply the results of a few errant beaver gnaws. 

I was wrong. When the beavers fashioned a pond beside a grove of hemlocks, they began cutting down bigger trees

And then the beavers began stripping the bark off the larger hemlocks.

I think the beavers got into the habit of stripping the hemlock bark and using it for their bedding inside the lodge.  Anyway they cut or girdled just about all the mid-sized to small hemlocks.

Needless to say all those hemlock died. I can take a larger view of that. Thinning a stand of hemlock generally increases biodiversity. And I looked forward to the beavers fattening themselves on the grasses and shrubs that would now grow along that shore, but the beavers left.

There were still plenty of large hemlock a bit higher up on the ridge. Last time I hiked down the valley,  a snowy morning in January 2014 three years after the beavers left, I saw porcupine trails under the hemlocks:

The sharp quills of the porcupine make it like no other animal. Beavers feast on grasses and so do porcupines. The beaver can't go far from its pond.

The porcupine can dine in the middle of a golf course fairway.

Plus those same quills that protect a porcupine from other animals seem to keep porcupines from getting close to each other which can keep a stand of trees from being overwhelmed by crown trimmers and bark scrappers. I rarely get photos of porcupines close together and at first glance the one below shows two remarkably close.

But they are on different trees. Such is the porcupine's lonely trajectory through life. To be sure, I have seen porcupines on the same limb, but there is no better emblem of mutual discomfort.

Plus those two were screeching at each other. Seeing beavers together, especially in the winter, invariably warms me.

Porcupines together usually means screeching if not a fight:

Any animal that grazes on the ground or up in trees makes an impact on surrounding vegetation, but that impact is minimized when the animal generally grazes alone. To be sure porcupines mate and have off spring but usually just one baby porcupine.

I have often observed the exertions of beaver parents to feed their young. Once I was up on a ridge watching two kits swimming a bit aimlessly around the lodge. Then an adult beaver swam down to them and turned toward the ridge and climbed straight up coming within a few yard of me. It cut down a small tree behind me, cut off one of the branches and dragged it down to the kits who started eating the leaves. Meanwhile I heard something else crawling behind me. It was a porcupine, alone as usual. It stopped when it saw me and went on its lonely way. Too dark for a good video.

I did get a video of baby porcupine with its mother, characteristically walking away.

Let me note that in response to a threat, me in this case, mothers and babies of many species separate. But this separation was so slow, I wonder if they thought I was a threat.

By winter, as far as I've been able to tell, all porcupines will be alone. No need for caching branches or other food, like beavers and other animals do. 

My passion for beavers is evident and I have been woefully slow in observing how they change the land let alone understanding it. So all credit to the beavers, but there is something god-like about a porcupine.

If I was going to make a religion of my nature watching, I would find the Church of the Porcupine accessible and easy to find and if the little god wasn't inside, I might see It high in a nearby altar, and, if high enough, It invariably beams down on me Its prickly blessing, a soothing balm for an old man like me.