How an Otter Defines Its Territory and Home Range

Here again is a male otter with his mind on his business, which, on April 21, 1999, was marking part of his territory, a four year old beaver pond that I called Beaver Point Pond. This time we see him leave his mark, poop, which some call scat and others call spraint. At the bottom of this page I'll describe scats and briefly describe where otters generally scat. But the first question is: how do I know this otter was a male and was marking his territory? And if I am right about that, what is his territory?

Adult male otters can be up to 17% bigger than females, or so a study of Montana otters found, see Melquist and Hornocker "Ecology of River Otters in West Central Montana." This struck me as a large otter. Also, as I'll explain below, by this time in the Spring many female otters have just had their pups, and would not look as carefree as this otter did, in my opinion. I have a video clip of what I think is a female otter scating at dawn on an April morning, another year and another pond, which I'll share below, but first, what is an otter's territory?

"Territory" might not be the right word. Wildlife biologists also use "home range", and "core area". But I like territory. I see the way that otter stamped his feet. That says territory to me, and here's my rough idea of this otter's territory:

Eel Bay is about two miles across. I think the territory goes quite far down the American channel, at least another four miles down to Brown's Bay to the northeast. Beaver Point Pond, where I saw the otter in the video above, is below the pond marked with a D, which is what I call Otter Hole Pond. Both ponds are now more or less meadows. When this satellite photo was taken Beaver Point Pond didn't exist. The beavers had not built the dam that created the pond.

I am pretty sure this is the territory because of the pattern of otter slides I see in the winter, going from island to island and out to the channel, and from the similarities of the otter scats I've seen around South Bay and around Eel Bay, and because I've seen otters swimming from Grindstone to Picton, half completing the circle that's Eel Bay. As the short video clip below shows, that is quite a different environment than a beaver pond.

I can't prove that the otter glaring at me off Picton Island is the same otter glaring at me in Beaver Point Pond on April 21, 1999. The otter in each video seems to have the same style. At what is called Quarry Point on Picton Island (100 years ago granite was quarried there and much of it went to build the Museum of Natural History in New York,) otters frequently leave their scat. The photo below, taken from a less frequently used latrine on Murray Island, shows the commanding position of Quarry Point in the distance:

Now, this is what I think an otter's territory means: it's where male otters not related to this male better not make themselves too comfortable as they pass through and this is where the female otters the resident male mates with can raise his offspring with some guaranty that unrelated otters will not move in and compete for the fish, frogs and crayfish that otters here eat. Of course, the territory is also used by the females and offspring of the otter, but for at least half of the year, each mother and her pups will range in their own small corner of the territory and have it mostly to themselves. The map below shows where I've principally tracked otters since 1994 and between April and November the mother and pups I watched probably spent most of their time there.

I've seen evidence that the mother otter is not a passive occupant of her territory, even as she cares for her pups. On September 13, 2004, I saw a mother and pup break off their napping on a lodge on the north bank of Second Swamp Pond to drive away another mother and pup who were coming down the pond from the east.

 

I think this video shows that the invading otters had a nice understanding that they didn't belong because they retreated without any screeching or bluffing. That said, the defending otters seemed to expect as much, as they were none too aggressive and they resumed their nap on the beaver lodge. Other observers suggest that female otters mark and maintain territory just as the males do. I think it is generally held by wildlife biologists that otters respect territory and try to avoid confrontation. Indeed because otters are so well mannered and don't butt heads to the near death, as we've become accustomed to see other animals do in nature films, there seems to be a tendency to discount the importance of territory among otters. The more I watch otters, the more I think their sense of territory is essential to their survival, a point I'll return to later.

But that makes the otters' world sound a bit too orderly. Two days after I saw the male otter scatting on a mossy bank of Beaver Point Pond, I saw, at the same pond, that it is a bit more complicated, since in this case it was hard to tell if an otter was actively defending territory or merely exploiting it to full advantage. There was a strong wind and as I sat below the dam watching a beaver, I heard screeching coming from the south shore of the pond, from that ridge where I saw the otter scat two days before. I soon saw an otter down on the bank next to the water, and then I saw a splash, heard some more screeching, and then I saw an otter on the bank and another otter in the water swimming away. The otter on the bank kept looking at the pond. The otter in the pond swam to the middle of it, dove, brought up something on a log and nonchalantly gnawed on it. The video clip below shows the brief fight as I saw it, and then a lull as the male otter, I think, makes his slow way to a log out in the pond.

Was the otter on the bank defending territory? or, was the otter in the pond relaxing from a sexual encounter? If the otter was defending territory, it did a poor job of it since that other otter was quite comfortable in the middle of the pond. My guess is that the encounter had something to do with sex.

As I'll try to demonstrate with many video clips later in this "book", it takes about nine or ten months to properly raise an otter pup, especially when a mother has the usual number of pups, three. It takes about two months for otter pups to gestate in their mother's womb. So the otter mother is busy year round carrying or raising pups. The best time for animals to be born or hatched, for that matter, is in the spring. That's a nice time to first see the light of day and affords a good six months for the new arrivals to fatten up and prepare for the challenge of winter. To make sure that pups are born around April 1st, in otter mothers, and many other animal mothers for that matter, the implanting of embryos is delayed. That means an otter can have sex without immediate consequences. The blastocysts that result from successful mating simply float in the uterus until months later they become attached to the uterine wall so they can be nourished and develop. (Or so I read, no videos of this process!)

So that pups are born in April, implantation occurs sometime in late January or early February. Given the mother otter's busy schedule the only window she has for having sex is from that time in February when she separates from her pups until late April. According to Whitaker and Hamilton's Mammals of the Eastern United States, otters can been in heat 42 to 46 days after bearing their pups. This makes sense because newborn otter pups are rather helpless, can't swim or scoot about, so the mother can take time off from suckling them and get out and find food. So I'm suggesting that on April 23, 1999, a male otter was still inclined to have sex, while a female otter may or may not have been in heat even as she was caring for new born pups.

Screeching is characteristic of otter sex. They are supposed to do it in the water. As I see the video, one otter was always on land. But I had been hearing screeching for a while, but all coming from that shore, not from the pond. Don't ask me why a male otter couldn't figure out that the female was not in the mood. He likely had already mated with that female otter, and, well, perhaps the screeching encounter had some satisfying consequences for him. How else explain why the otter who seemingly had the worse of it along the bank seemed so fat and happy out on that log in the middle of the pond?

So while otters might sort their territory out in orderly fashion, there is no lack of tension within that territory because of the battle of the sexes.

To make this point more clearly, I need to establish that female otters nursing and raising pups have no use for male otters, that no father is needed, other than for that brief encounter that leads to mating. I'll give it a try. At dawn on April 15, 2001, I went out to a pond to watch the beavers, and while I watched the beavers, an otter appeared in the pond, scatted by the dam, did a bit of fishing, saw me and disappeared. But this otter did all that without the cocky demeanor of the otter I saw on April 21, 1999, who is featured in the video clip at the top of this page. I think the otter in the video clip below is a female, a mother getting away briefly from her pups. At the time and when I first studied the video clip, I thought the otter was wary of the beavers nearby. Indeed, as she got back into the pond after scatting she screeched to persuade the beaver to move aside. But maybe she also has an eye out for a touring male otter.

This took place in the East Trail Pond and opens with a beaver slapping its tail. I thought that slap was meant for me. Then an otter swims into view coming from the direction where, I would later determine, an otter mother made a den in a tree trunk to raise her pups. The otter has more beavers to get past and I used to think all her looking up as she swam arose from her concern about the beavers. I have seen several other otter-beaver encounters, and in most, as was the case in that June 2001 video clip I shared on page 1, the beaver was the aggressor and the otter or otters in the beaver's sights seemed more put out than alarmed at the attention. This otter, I think, was looking beyond the beavers. You can see that especially when it gets on the shore and looks up the hill at the 1:30 mark. After scatting on the shore -- I couldn't see that and edited it out of the clip -- the otter goes back through the pond not too worried about the beavers even as it gets another tail slap. The otter starts looking around again, but now I think it senses my presence. I love studying this video clip, but will admit what it doesn't prove my point that female otters are shy of males once her pups are born.

I do have a more persuasive clip. It shows a mother hiding her pups and herself from a touring otter, and also involves a beaver. On October 21, 2005, I had watched an otter mother and her two pups fishing in the Second Swamp Pond for about an hour. I had remained undetected and when they went up to the next ponds, I followed. I went up to the Lost Swamp Pond where I didn't see the otters, then I heard a beaver's tail splash and an otter screech down over a slight ridge at a new pond the beavers built above the Second Swamp Pond. When I went over to see what was happening, I saw a beaver swimming back and forth in front of his lodge, but I didn't see any otters. Then a lone otter swam down the pond and went over the dam down to the Second Swamp Pond. The beaver didn't do anything. After that otter left, the mother came out from the beaver's cache of sticks, snarled at the beaver, and resumed fishing with her pups. Here's the video clip:

The lone otter was probably a male, and probably related to the other otters, but the mother simply didn't want to have anything to do with him. Since April she had more or less exclusive use of the ponds and wished the interloper away.

On the next page, I'll get back to the otters in Beaver Point Pond in 1999 where I am pretty sure a mother raised two pups. But before leaving this page, I should try to explain some otter fundamentals.

One of the keys to understanding the otter that graces the top of this page, and the life and adventures of his consort and offspring, is to understand what he left behind up on that ridge. After the otter left, I did take some video of his scat. I didn't carry a camera then, and video is not very dramatic. So let me put in a video of another male otter marking territory, in 2005, in the Lost Swamp Pond.

By 2005 I was taking a digital camera in my camcorder bag and so I got a good photo of what that otter left behind. In the video clip below, taken June 4, 2005, I saw an otter swim quickly through the large pond, only pausing to dive for fish a few times, and then go up on a slope and scratch up grass and scat, perhaps even make a scent mound. He scats like the other otter, then humps about like a crazy cat scratching the grass:

When the otter moved on, I walked over to see what he had left behind. In the photo below you can see where he scratched up grass and left a scat.

What's otter scat like and where do they usually scat? These are valuable things to know if you want to look for otters. Fortunately for otter watchers, what's left behind is easy to identify: loose, usually black, filled with fish scales, even fish parts, and smelly. Here's the scat that 2005 otter left behind, and then three more for your pleasure.

 

I have hundreds of photos of otter scats, but I've noticed that not many people appreciate otter scats as much as I do. So I'll put a selection of otter scats on another web page: SCATS All otters scat around the ponds, not just males, often in groups and often at the same place. Finding their latrines can be a great help in tracking otters. Not only does it show where otters have been, it can also indicate how recently they've been there. Unlike raccoon scat and deer droppings, otter scats usually age quickly. Good places to look for otter latrines are on rocks beside the pond (as the video clip above demonstrates,) on likely trails into the pond, on beaver dams and, if you can get to them, on beaver lodges.

Sometimes otters seem to make a more formal arrangement, scraping up grass in a mound and crowning it with a scat. I assume they make these in areas significant to the other resident otters, and where they are likely to be noticed by non-resident interlopers. For example, here is a scent mound

that was on the ridge between the west end of the Lost Swamp Pond and the east end of the Second Swamp Pond.

Otters often make scent mounds

at a latrine high on the north shore of South Bay overlooking the entrance to the bay

Otters can get a bit manic about making scent mounds. In the Spring of 2005, no less than nine scent mounds lined a little causeway that carried a trail over a pipe that brought the water from the Big Pond and the little ponds below it into South Bay.

Now, back to the Spring of 1999.

Turn the page to see the next videos: Page 3

Here is a rough guide to the video clips contents in the video book.

By Bob Arnebeck mailto: bobarnebeck@gmail.com