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The death experiment


One of the most common emails I get in my inbox is: "How long does it take for a body to decompose ?" (Yep, my inbox can be a bit weird at times). But this is useful to know, because if you find a half decomposed body you can work out when it died, and when the bones should be clean by. So here's my expert answer based on all my years of experience:

I don't know. 

I don't know because it all depends on so many different factors that it's almost impossible to tell. I've seen a juvenile red deer which was reduced to white bones in three months, or the badger had still had most of its skin intact after eight months, and it depends on weather, size of the animal, temperature, and all sorts of things. This week's post is about an experiment I have been doing to try and learn more about how long decomposition takes. (Warning: it's a bit yucky in parts !)

The winter roe deer

This was a lucky find - lucky for me, of course, but not for the doe, who looks like a young female, maybe 18 months old.

In October I began checking out a new wood where I thought there might be otters. It was wet, marshy underfoot and it was hard to walk through, but I have seen deer on the corner of the wood on my way to school. I found there were red deer, which I wasn't expecting, and set up the trail camera to film at a mud wallow, and found a ground of about ten hinds and youngsters that passed by at sunset each night. Then a bit further up from the wallow I found this  body of a roe deer on the 7th of December, and it looked very fresh indeed, and I thought it had probably died the previous night.

About half the wood if open pine forest, and the other half is very dense pine, and inbetween the two is this thicket of trees. The body was in the middle of this, on the other side of the trees to the right, in a spot where roe would be unlikely to go. The trees form a U-shape, so it is easy to go in, but difficult to go out.

The body was in a very unusual position, lying with its neck underneath the tree. It's possible it was dragged there after death, but there were no obvious signs of death. It had a tiny fleck of blood on the back of its neck but no open wounds, so I'm not sure how it died.

I was expecting something to come and eat it, so set up my trail camera to watch the body.

When we first found it, it still had its eyes, which are the sometimes the first signs of predation (being eaten) because birds can peck them. The eyes were clear at first, but two days later they were starting to go cloudy.

After 14 days, there were very few signs at all of death. During that time the temperature had been between about 10c and -2c, and was mostly between 0-5c.By this point, the eyes have gone solid white, but there were very few signs of decomposition and no obvious smell from a few feet away.

After another ten days, there is still not much change, although the fur is starting to look shabby, and the eyes are pure white.

So this happened a lot differently to what I was expecting. The first thing I was expecting was that decomposition would happen much faster, whereas the body now looks very much the same as when it first died a month ago. The second thing was that I expected more predators on the body, but the only animals which have been near it have been a robin, a goldcrest (yeah !), and.....

... a pine marten ! This is the third time I have set the camera to film something, and I have got a pine marten instead. I have a good idea about where this pine marten is nesting as well. The pine marten had been sniffing round the body, and marking it with scent, but not doing much more at all, although it's pretty cool to see them at all.

So why did I think decomposition would be much faster ? This is why:

The summer roe deer

Over the summer I moved the trail camera from the pine marten wood on the moor to a red deer wood. I found this body on the 4th August, just before I went back to school last summer, lying by the side of a quiet country road after being hit by a car. From this angle it seems pretty intact, but...

Very gross image. Click and hold down to see the full picture or click here to see in a new window.

As you can see, the back left leg had been completely removed at the hip and taken away, almost certainly by a fox. I never found where it ended up, but at the time I did film the fox going past the trail camera with something in its mouth. This is why it's not unusual to find just two legs with a deer skeleton, because the rest may have been taken away.

Eight days later, and the fox had been snacking away more:

Very gross image. Click and hold down to see the full picture or click here to see in a new window.

Foxes often start going into the chest cavity from under the back legs, where the skin is soft, then pull away the insides without having to go through the hard rib cage. Here the fox (and probably buzzards and red kite as well) have been working up the body, and breaking the ribs as they go. The spine is still intact because the soft tissue between the vertebrae is very tough, and the last part to decompose.

After sixteen days in a not very hot summer, the remains look a bit gruesome, but they are almost skeletonised:

By 36 days after death, the skull was entirely clean.

So why was this one reduced to a skeleton in 36 days, but the winter roe looks pretty much the same ? I think the heat of summer makes a big difference, as well as more flies laying eggs which turn into maggots.  It was in a place where it was easy to spot it from the sky, and where a fox, crows, buzzards and red kite lived nearby. The winter roe was hidden, not visible from the sky, was in a wood where there aren't many crows, and was inbetween two farms, one of them a sheep farm, so foxes would be discouraged. (But read to the very end for another update)

The predated roe deer buck

For much of last year my trail camera was on the moors in the two pine marten woods, and I also wrote about the roe deer that lived in the same woods. I hadn't been up there for ages, but found this roe buck last weekend (on the 4th January). Although I thought I knew all the six bucks in that area, this one was a different one.

It still has the spine tissue intact, so looks a lot like the summer roe did at 16 days, which would mean it would have died around the 18th December. But it couldn't possibly have died then because it has a full set of last years antlers, and in roe deer the antlers fall off in late November or early December. But I literally have no clue when it died, but if I were guessing I would say September or October.

There are other signs of predation. The nose has been bitten off, which is either a sign of foxes wanting to get at the blood-rich tissue inside, or a sign it was killed by a big cat, depending what you believe.

Normally foxes bite through the belly, go under the ribcage and take organs from there, but here the ribcage has been cracked open.

I had a good look around for the front legs, but couldn't find them at all, which is not unusual.

But there's a twist !

I always write my blog posts a few days in advance, and today I asked Dad to check the trail camera for me, because it hadn't been checked since the 2nd. This is how he found the body today:

The body had been dragged out from under the tree, and the body had been ripped at the back leg. What could have possibly done it ! Well, I know, because it was all caught on camera ! I'll blog about that some other time !

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Jo said...

Fascinating, Jake. A great scientific post. Have you got (or can you get) the local temperature/weather conditions since death? I'm very surprised by the slow decomposition but then perhaps I shouldn't be. As you say it depends on so many factors. Looking forward to the next part...

Jake said...

I know the temperature because it's only a few miles from my house. But I haven't been taking the exact temperature every day.

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