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Aging Animal Scats – A Study with River Otter Scats

Published on August 20, 2014 under Articles

Aging-Otter-Scat

Researchers often use scat (feces) counts as a way to determine abundance of various species. The basic idea is that if you know the rate that an animal defecates (say 3-4 times a day), and you’re able count scats from a known window of time, then you should be able to estimate the number of individuals in a given area. The problem is that it can be really tough to make sure you’re not counting old scats.

This article compares fecal pellet count methods and explains the importance of estimating scat decomposition rate.

One method to ensure only fresh scats are counted requires researchers to search the survey site and mark or remove all the scats before the survey. Another method requires surveying after a snow. Some methods though require the observers to age the scats. I once worked on a project in Colorado where I had to count elk pellets from this season only. Even though the goal was to identify scats that are a year apart in age, it was not always easy.

Here’s an article on the decomposition of different rabbit scats.

Accurately aging animal scats can be extremely challenging. Weather, contents, and location can dramatically effect the way a scat ages. In fact, two scats of the same age placed a few feet apart may age at dramatically different speeds depending on the microclimate in each location.

A River Otter Scat Experiment

In 2005, my wife and I worked as wildlife technicians for a river otter project in Missouri. The project required us to canoe roughly 10 miles a day along different rivers and search for river otter scat. I decided this was a rare opportunity to collect extremely fresh otter scats (sometimes called spraints, feces, or droppings) and document how they age.

I placed scats in either the sun or the shade, documented the weather, and took daily photos. All told, I did this with 5 scats in the sun and 3 in the shade. In order to reduce the number of photos in this post, I decided to only post photos from 1 scat placed in the sun and 1 placed in the shade. The scats used in this study contained entirely crayfish.

River Otter Scat in the Sun

(Click on the images to view full size)

River Otter Scat in Sun: Day 1

River Otter Scat in Sun: Day 1

The fresh scat is compact, moist, and dark red.

 

River Otter Scat in Sun: Day 2

River Otter Scat in Sun: Day 2

The scat is looser after just 1 day in the sun.

 

River Otter Scat in Sun: Day 3

River Otter Scat in Sun: Day 3

Note the dramatic change between day 2 and 3. In only 2 days the scat has lost much of its red color.

 

River Otter Scat in Sun: Day 4

River Otter Scat in Sun: Day 4

River Otter Scat in Sun: Day 5

River Otter Scat in Sun: Day 5

River Otter Scat in Sun: Day 6

River Otter Scat in Sun: Day 6

After a rain, much of the red color returned to the scat.

 

River Otter Scat in Sun: Day 7

River Otter Scat in Sun: Day 7

River Otter Scat in Sun: Day 8

River Otter Scat in Sun: Day 8

River Otter Scat in Sun: Day 9

River Otter Scat in Sun: Day 9

After a few slightly drier days the scat has lost much of the red color.

 

River Otter Scat in Sun: Day 10

River Otter Scat in Sun: Day 10

Even after 10 days, the red coloration returned to the otter scat after a light rain.

 

River Otter Scat in Sun: Day 11

River Otter Scat in Sun: Day 11

River Otter Scat in Sun: Day 12

River Otter Scat in Sun: Day 12

River Otter Scat in Sun: Day 13

River Otter Scat in Sun: Day 13

After several days of rain and a persistent reddish color in the otter scat, a single day of sun has resulted in a complete loss of the reddish coloration.

 

River Otter Scat in Sun: Day 14

River Otter Scat in Sun: Day 14

River Otter Scat in Sun: Day 15

River Otter Scat in Sun: Day 15

River Otter Scat in Sun: Day 16

River Otter Scat in Sun: Day 16

River Otter Scat in Sun: Day 17

River Otter Scat in Sun: Day 17

After 17 days of aging, I flipped over the scat and found the underside to still contain a strong red coloration.

 

River Otter Scat in the Shade

Otter Scat in Shade: Day 1

Otter Scat in Shade: Day 1

The fresh scat is shiny, moist, and a consistent dark red color.

 

Otter Scat in Shade: Day 2

Otter Scat in Shade: Day 2

Otter Scat in Shade: Day 3

Otter Scat in Shade: Day 3

Notice the dramatic change in the scat between day 2 and 3. I believe insects may have fed upon the scat during the period between these photos.

 

Otter Scat in Shade: Day 4

Otter Scat in Shade: Day 4

Otter Scat in Shade: Day 5

Otter Scat in Shade: Day 5

Otter Scat in Shade: Day 6

Otter Scat in Shade: Day 6

Otter Scat in Shade: Day 7

Otter Scat in Shade: Day 7

Otter Scat in Shade: Day 8

Otter Scat in Shade: Day 8

After 8 days of almost continuos sun, the scat is almost completely bleached white.

 

Otter Scat in Shade: Day 9

Otter Scat in Shade: Day 9

A day of rain and the color quickly returns to the scat.

 

Otter Scat in Shade: Day 10

Otter Scat in Shade: Day 10

Notice how fast the scat in the shade aged in comparison to the scat in the sun. In all the tests I ran, the scat in the sun seemed to be baked into its shape and relatively resilient to falling apart. However, scats placed in the shade stayed moist and were more easily fed upon by beetles and other insects. The moisture also allowed them to stay soft which resulted in faster decomposition.

So What Does This Mean?

This basically means that scat aging is really tough. I take comfort though in something I learned about the San in the Kalahari Desert. They are some of the last people to practice persistent hunting where through a combination of excellent tracking and fitness are able to run down game until the animal collapses from exhaustion. They classify tracks into 3 basic categories: very fresh, fresh, and old.

  • Very fresh: the animal is extremely close and we must approach quitely.
  • Fresh: the trail is fresh enough to find the animal.
  • Old: the trail is too old to follow.

There are some great tips on aging tracks in Practical Tracking: A Guide to Following Footprints and Finding Animals (Link to Amazon)

It is relatively easy to tell the age of a scat when it is extremely fresh. But as the scat ages, the difficulty in determining it’s age increases as well. This rule holds true for tracks as well.

Thoughts on this article? Feel free to comment below and I’ll do my best to respond.

5 Comments

  1. Mike Lowing

    A really useful article Jonah – thank you.

    In several areas of the UK, regular otters surveys are conducted whereby we hope to find fresh (night before) spraint and, with many assumptions about spacing, group size etc., try to get a rough idea of population – or at least (by being consistent in our assumptions) population trends. The identification of truly fresh spraint has always seemed highly subjective and the gold standard is to visit sites on two successive days and record spraint only on day two. However,it is tough to get commitment from all the survey team (I have 50+ here in Dorset) for two days in a row and we have done our best with the subjectivity so far. Your study inspires me to do the same here – we have a different species, different prey and certainly very different weather so it will be interesting to compare. I shall be advocating this in a training session at the end of the week – and using your pictures to show what can be done. I hope this is OK – I will acknowledge the source obviously. If you should see this comment and were able to make the photographs available in full resolution (perhaps via Dropbox?), that would be great but I think I can make the point with screen captured copies.

    Thanks again for the excellent example.

    Best wishes – Mike

      1. Mike Lowing

        Thanks Jonah but I saw that I had been dumb not to spot that clicking on each photo gave me a better image with plenty of resolution.

        I will let you know what we do and the results we get.

        Best wishes

        Mike

  2. Marianne

    Hello – I came across this article as I tried to find studies that discussed the ecological benefits of otter scat. I was doing so because my family owns a very small island which is shared with a large family of otters. There at tons of crayfish in the lake and the feces, consisting predominantly in these, are EVERYWHERE. I was trying to determine whether to get rid of it all, or to gather it to use to build up parts of the island / soil… Do you know anything about the effect decomposing otter poop has on soil quality? (Alkalizing is my guess but I don’t know)

    1. jonahevans

      Marianne,
      Thanks for your comment. I’ve never thought to look at the effect of decomposing otter scat on the soil. It’s a very interesting idea.

      I have seen frequently used otter latrines that have killed grasses (or at least turned them brown). The effect of fresh scat might be much more damaging to plants however than old, decomposed scat.

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