Friday Weird Science: SCIENCE! Keeping an eye on your dead skunk since 2011.

Oct 21 2011 Published by under Friday Weird Science, Uncategorized

All animals used in the present study were already found dead (road-killed), and therefore an ethic approval is not required.

You know, sometimes I see a study (this one was tweeted around a few weeks ago), and you just sit and wonder WHY. Why did scientists DO this study, why was it necessary? What is its purpose in life? I mean, this one must have a purpose. It’s not like most people WANT to drive around counting and assessing the state of roadkill.

And indeed, this study DOES have a purpose. And it’s more than staring at roadkill.
(Though maybe that’s fun too? I mean, I’m not everyone)

Santos et al. “How long do the dead survive on the road? Carcass persistence probability and implications for road-kill monitoring surveys” PLoS ONE, 2011.

There are a LOT of roads in the world, particularly in developed countries. Where there are roads, there are generally cars. And these roads, and these cars, are going to have an impact on the environment around the road. The migratory patterns of the animals for example, not to mention the number of animals that like a piece of nice warm blacktop on a sunny day (snakes are a good example of this. Also armadillos. Especially armadillos. Ask a Texan). So where there are roads, and cars, and animals, well, animals are going to get hit by the cars. This means cleanup work, and efforts by ecologists to try and prevent some of roadkill carnage. And this means that you have to actually figure OUT just how much roadkill there is. For this, you have to know how long a given piece of roadkill is going to remain on the road before getting eaten or squished into something entirely unrecognizable. If you’re only driving around once a week, you may not catch all there is and your numbers may not be reliable.

This requires dedication. This requires scientists driving around in a truck over the same patches of road, day after day, counting roadkill.

Let us have a moment to pause and think of those poor scientists, and for our eyes to water on their behalf. For truly, they have sniffed the stink of many dead skunks.

(pause)

TO THE ROADKILL!

The scientists observed over 4,000 specimens in a typical Mediterranean forest in Portugal, over a period of about a year. The vast majority were small birds, salamanders, and toads, and the rarest roadkills were turtles. By far. Considering the slowness of the turtle, I think we need to think for a moment about their possible craftiness when faced with roads. A few large carnivores and large birds were represented as well. There were also 82 bats. BATS. This is the point where I looked up and exclaimed to Mr. S “people hit BATS while driving?!” If you are a person who has done this, please report in.

But the other question is, how long do these carcasses PERSIST? After all, dead meat is dead meat, and to many animals dead meat is tasty. Not only that, you’ve got other cars coming along to squish your carcass into oblivion. So the scientists came back day after day, each time they found a new carcass, to see how long it lasted. From this, they computed the somewhat amusingly named “survival curve” (for the survival of the carcass, obviously, the animal’s been toast for a while).

You can see that the toads, salamanders, and bats had by far the worst of it. Though the toads and salamanders were among the most often hit, they, along with the bats, persisted in most cases for less than a day. Too much traffic on some very soft anatomy. The longest persistence was credited to the carnivores, the large birds of prey, and hedgehogs, which had a 40% probability of making it to 15 days by the side of the road. In the middle you’ve got your small mammals, your bunnies, snakes, etc.

So what does this show? Well it mostly shows that other estimates of roadkill had a lot of bias, being biased toward carnivores and the larger animals, because those were still around when the trucks came by. Most other estimates show toads and salamanders and such represented pretty low, but this study indicates that this is because they just don’t make it that long.

But it makes me wonder. This was Portugal. They don’t really report things like deer (do deer live in Portugal?). How would this differ in parts of the US? What is the persistence time of armadillos? What of skunks? Clearly we need to be eyeing our roadkill more carefully. It might be gross, but it can tell us a lot about what gets hit, why, and when, and can help us find ways to save some animals from that deer in headlights look.

8 responses so far

  • Mike says:

    I recall a lot of Hedgehog persistence in the UK. You'd find a few spiky pancakes along a country road. Hardly ever a bird, squirrel or rabbit in the same state. There's a general feeling that a lot of Hedgehogs die on the road, probably due to the persistence.

  • CyberLizard says:

    I recently started riding a Vespa for commuting 25 miles to work everyday. One interesting side effect is noticing all the roadkill. By smell. Ugh.

    I'm down in Florida, USA, and I mostly see (in descending order by frequency) armadillos, opossums, squirrels, raccoons, cats, and dogs. Only once or twice have I seen a deer or a black bear and never on my usual commuting route. Usually the armadillos and opossums will last a couple of days. Squirrels become a greasy smear on the pavement quite quickly. I suspect that cats and dogs don't last very long because they would tend to generate more calls to the county/city to come clean them up, though that's just a hypothesis.

  • Anne says:

    Oh my goodness, my mom would love this study. Mom has thought about teaching a short course on road kill ecology, and we definitely had a copy of the Roadkill Cookbook in our house growing up. (Not that we ever tried any of the recipes.)

  • Dirkh says:

    Up north on roads in the boreal forest of the U.S., we're top-heavy with big (and potentially destructive) road kills like white-tail deer and moose. Definitely underrepresented at the salamander end of the animal world.

  • Mika says:

    Tasmania poses another interesting case study, in that tasi devils are scavengers. Roadkill becomes an intensifying feedback loop, where something dies, the devil scurries out to eat it, eats until it's bloated and goes into a food-coma, gets hit, becomes roadkill, then a new devil scurries out to eat it, eats until it's bloated and goes into a food-coma, gets hit...

  • gnot says:

    I live in the Northeastern US, and it varies significantly by season. There's a squirrel season, a fox season, a time for porcupines, etc. Deer all the time though. And you may actually not see the salamander/frog kills if you aren't driving around on the right roads around 3am regularly. The roads are literally paved in dead frogs and salamanders, in patches hundreds of feet long. By morning they are all gone - they feed legions of foxes and skunks and who knows what else. I bet those poor bastards had to do this at night too. Maybe hourly. I don't know how you'd separate out those frog carcasses though, it's literally that bad.

  • when I drive a car in Florida California.I will see the dead dogs rats cats etc.I feel that the dead doesnot long.Thanks for good information that comes out to read

  • Danger says:

    Wait... How is carcass survival measured exactly?

    Is it time before it is ground into the road or until the carcass is scavenged?
    If it's the former, how do you quantitate that??? Also, in this case wouldn't the curve heavily depend on where the carcass comes to rest after getting hit?

    Toads and salamanders and the little ground dwelling critters are likely to stay right where they are when they get squished (which is in the tire zone) while birds of a feather and larger beasts have a higher chance of being thrown off to the side. Those guys would be less likely to be repetitively flattened by cars and therefore have a longer 'survival' curve.