I figured it out! STOP PRESS! - Tactical Ninja
Feb. 10th, 2013
10:01 am - I figured it out! STOP PRESS!
So you know how yesterday I mentioned that the flystruck ewe had tipped over into the resigned stage and that this is a thing sheep commonly do when sick? I've always wondered what kind of evolutionary advantage they gained from doing that - how does lying down and going "Oh woe I am going to die but I'll accept that gracefully, come get me predators..." is helpful to survival. Then I realised I was looking at it wrong.
Sheep survival depends on two things:
1. Flocking together - safety for sheep is in numbers because otherwise they are slow, defenceless and tasty.
2. Being prolific. They can produce and rear offspring in remarkably adverse conditions, and multiple births are common.
We're looking at number 1. Sheep hang out together - even when they aren't disturbed, they'll distribute themselves so they can always see at least 2 or 3 of their flock mates. They only go off by themselves to lamb, and even then another sheep will often stay within sight of both them and the flock, acting as a sentry.
When a flock is threatened, they all mob together tightly. The ones in the middle are safest and the ones on the outside press towards the middle. When approached closely, they scatter like a school of fish and then flock together again at a distance. I think this is confusing to predators, and means that the relative chance of being grabbed decreases as the size of the flock increases.
Anyway, an important part of this flocking behaviour is Not Standing Out. Those that stand out are more likely to be grabbed, especially if they show some sign of weakness. Predators are always on the lookout for easy prey. So, if a sheep is sick, it'll hide it as much as possible. Remember yesterday's sheep, and how subtle the signs of illness were? And she was pretty close to keeling over.
So instead of looking at the 'resigned' stage as an evolutionary advantage, what I should be looking at is the way in which sheep hide their illness until they are so far gone they can't stand up any more. THAT is the evolutionary advantage, because that is what will help a sheep that's sick but going to pull through to survive in a flock - to not stand out for predator-grabbage, to be taken on casual glance as healthy.
And when they fold (which is the terminology for lying down and going WOE IS ME), they really are completely exhausted and possibly close to death. It's not an illness-response, it's an inability to produce the illness-response any more through having used all their reserves hiding their illness.
Gosh, sheep are a lot like people.
Yes, that really did keep me up last night.