Why do some animals defaecate indiscriminately?

04 September 2011

Question

What's the zoological term for animals like horses and rodents that defaecate indiscriminately anywhere, anytime? Is there an evolutionary advantage? My guess is, if you have to stop what you're doing every time you want to take a poo, it makes you kind of a "squatting duck" for predators.

Answer

Emma - Right. The answer is actually rather messy, if you forgive the pun, because there isn't a definitive answer and I don't know if there is zoological term for animals that just go whenever and wherever versus those who can hold it. I think it's just termed bowel control or lack of bowel control. Whether an animal goes everywhere or they go off to do it somewhere specific depends on the nature of the poo itself, which might be dependent on the food that the animal eats. It tends to be that very non-toxic vegetarian poo, which is no harm to the animal at all, can be done wherever and there's no danger to the animal being around that poo. You'll definitely notice if you have rabbits or guinea pigs that they just poo all over the place. In fact, guinea pigs even eat their poo, which is really disgusting to us but great for the guinea pig because it gets an extra meal. In comparison, animals with more nasty, parasite laden poo tend to go off and poo somewhere else. Horses in a field tend to poo in clumps and they never feed around that clump so the grass gets really long. They do this because they can have some really nasty kinds of worms and parasites that get inside them if they ingest anything which lives in their poo. Birds as well, you'll notice, always have clumps of poo below the bird's nest, but they don't intend to pooh in their nest. In fact, some birds actually remove poo out of their nest and carry it off and drop it somewhere else. That's thought to be to do with the parasite burden. Another dimension to this is actually communication. You'll know that many animals communicate using smell. Big cats such as cheetahs or lions out in the savannah tend to poo out in the open deliberately to mark their territories. In fact, that's often how they're tracked. Hippos use their tail to actually swirl poo around in the water where they go, again to mark their territory [and to flick it into trees and shrubs on land, for the same reason]. As you mentioned in the question, being caught as a sitting duck and not wanting to be caught by predators, that could also have something to do with it. So again, horses and animals such as deer can definitely poo while they're actually running along. So I should think that's useful. I hope that answers the question.

Dave - I guess, also, there's a big difference between herbivores and carnivores in that herbivores have got to eat a huge amount more food, which means there's a lot more to go out the other end [so pooping on the move is definitely advantageous...]

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