Wednesday, March 11, 2009

A Marked Otter

Lars posts two photos from 2/8/09. I followed this otter's trail across several hundred yards of one of the northern marshes of Delaney Complex in Stow. Throughout the trail, there were marks of distinctly red to reddish-brown color. The color was not found while the otter was in the woods, only on a long stretch of the trail in the open marsh. What is the color spectrum of scent gland markings? It seemed to have the color of blood. Rezendes' book speaks to otter scent secretion not only for marking, but also at times of fear or rage. Thoughts?


  1. Odd, it does look like blood. I've only seen the thick, goopy, all-in-one-spot type of scent markings; this looks much thinner than that. And mostly on the left side. Maybe it pricked a paw in the woods, before heading out into the open marsh?

  2. Great photos, comments, and questions. That does look like blood, but there seems to be some in the tail drag and a little in the right track in one of the photos, as well as in the left track. Lars, you had asked off-blog if this could be a female in heat. I thought not, since mating usually occurs in spring, shortly after the birth of the current spring's babies. This spring's embryos will then lay dormant until next winter, when they finally implant in the uterine wall and begin to develop, with birth occurring in spring 2010.

    But now I am wondering about the timing of events for a young female's first year breeding. Could she mate in winter and implant immediately, or after a short delay? I would imagine this is possible, since the "delay" in delayed implantation is probably not fixed. Implantation is thought to be triggered by day length, to ensure that birth occurs at the time of greatest food availablity, regardless of when mating took place. So, a female in estrus could explain the blood, I guess.

    Or maybe the otter was injured, or got bloody handling prey.

    You ask about the color of secretions. Rezendes and Elbroch comment on a mucous secretion that appears white on dark ground or yellow on snow. This is what I have seen. No one seems to be sure where this comes from - the anal glands, or some other part of the intestinal tract. A slimy greenish brown or black jelly is sometimes seen. Trackers seem to assume that this is produced when the otter feeds on frogs, for example, which have no scales to appear undigested in the scat. But biologists who have studied otters in captivity say that otters produce this even when they haven't fed at all for a day or more. So, it's possible that this has scent marking but no eliminative purpose.

    You reference a comment about otters producing secretions "not only for marking, but also at times of fear or rage". But these may be one and the same. An animal need not know that its behavior has scent marking purposes, or gives it a survival advantage in some other way. The animal only has to do it. It might be some raw emotion, like fear, rage, anxiety, joy, or some physical sensation, such as itching, pain, pleasure, etc., that drives an animal to do what it does. A bear might rub against a tree because it is itchy, but the scent he leaves might also provide useful information about his identity, health, social status, etc., to other bears. If this keeps other bears away from his territory, then it gives him a survival advantage and nature will select for bears that rub against trees to relieve itching!

    Not to belabor the point, but we humans do a lot of things without thinking about how they impact the likelihood of passing on our genes. I wonder when in human history people figured out that sex eventually results in offspring. Are other animals aware of that at all?