Wednesday, February 17, 2010

Otter Obfuscation

Janet writes:

Otters are said to "slide downhill most of the time", and uphill only
"occasionally", so those at Vaughn Hills last week must have taken great
pains to through off trackers.

In fact, on that particular day, they decided to do more uphill than
downhill sliding. One photo shows some uphill sliding - you can see that
the animal had to frequently propel itself forward with its feet in
order to keep moving. There was quite a bit of downhill loping, even on
steep slopes.

On the ice, the otter on the right chose to lope, while the one on the
left slid. (The narrow slides going perpendicular to the otters'
direction of travel were made by the slipping hooves of a deer as it
crossed the frozen stream.) Most of the slides I found that day were
short, and on flat ice.

There was a stretch of 9 consecutive steps of 2-2 bounding, the first
time I've seen an otter use that gait with virtually perfect registration.

One thing that has been fairly consistent, at least in my experience so
far, is the tight grouping of tracks. You can see that discrete
grouping in the photos above. Sometimes the tracks within a group did
spread out, but not often to the point where it was difficult to
distinguish separate groups (which does often happens in fisher trails).

Why did they do so much downhill loping? I don't know, but the tracks
are kind of small for otter, so maybe they were young ones playfully
goofing around, and/or maybe they had been eating well, and did not have
to worry about moving efficiently to conserve energy.


  1. Love the last pic--a light dusting of snow over a black ice base often makes the best prints!

  2. Here's some thoughts: maybe a mother otter is trying to teach pups to slide better, and by demonstrating uphill the pups can see better. I often see slides next to loping. I assume the pups lope to keep up with the mother. This year I am tracking a family, mother and three pups, and compared to other pups I tracked over the years they seem rather immature. They haven't really shown a knack for sliding.

  3. Very interesting comments, Swamp Watcher, but it seems awfully late for the pups to be just learning to slide. They should be almost a year old, and will soon have to leave mom, who should be having her next litter within a month or so.

    Could these pups have been born late, such as sometime last summer, rather than last spring? Given the delayed implantation in river otter, I am puzzled as to how that would work. Implantation and development of the embryos are triggered by day length, as far as I know. So, even if the mother conceived these pups later than normal in 2008, implantation should have occurred at the normal time in 2009 because it is triggered by day length, not the number of months after conception. The whole point of delayed implantation is to ensure that offspring are born at the optimal time.

    That doesn't mean things never go wrong. Maybe they were born late for some reason that I just can't think of.....

  4. I think it's better to say the mom will leave the pups. I don't think slow development would have anything to do with late birth. Lots of things can go wrong. This is the first year I've tracked a family so long and seen so little sliding. I hope I can see the pups after the thaw and see what shape they are in. They seemed fine in December.