Why do smaller animals survive falls from larger heights? I remember thinking about this classic problem with my friends back in school and tried to work through it again from a physics point of view. It turned out that it is more complicated that I thought:
Why do smaller animals survive falls from larger heights?
I would specifically like to know how physical scaling laws affect the chance of survival of an animal, i.e. we suppose the animals can be modeled as the same shape but every length scaled by a factor $k$. There are two biological factors one has to assume, namely that animals have roughly equal density and the force a muscle can apply scales according to the cross-sectional area it has ($\propto k^2$). I think apart from that one should be able to get away with making reasonable physics approximations. So maybe to reformulate what I mean by the "why" in the question above: can the phenomenon that smaller animals survive falls from larger heights be explained by physical scaling laws?
 A: I can't claim to know the full answer, but it's amusing to note that this question has a fairly long history in biology. Way back in 1928, J.B.S. Haldane (my great-great uncle) wrote a popular-science article called "On being the right size", about the importance of scaling laws for biological anatomy. The following passage is relevant for the question at hand:

You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away, provided that the ground is fairly soft. A rat is killed, a man is broken, a horse splashes. For the resistance presented to movement by the air is proportional to the surface of the moving object. Divide an animal’s length, breadth, and height each by ten; its weight is reduced to a thousandth, but its surface only to a hundredth. So the resistance to falling in the case of the small animal is relatively ten times greater than the driving force.

Haldane claimed (without offering direct evidence) that the difference could be explained because of air resistance. The force of air resistance scales as $f_r \propto L^2$, where $L$ is a characteristic linear dimension of the animal. However, the force due to gravity scales as $f_g\propto L^3$ (assuming fixed density). The ratio of these quantities scales as
$$\frac{f_r}{f_g} \propto L^{-1}, $$
meaning that smaller animals are buoyed up more effectively by air resistance as they fall. 
I expect that there is probably more to the story than this, however, as noted in the comments, these sorts of experiments are tricky to get funding for...
A: Let me try. Let's take an elastic ball (instead of an animal...)  of radius $R$ and stiffness $k$, freely falling in air. The ball breakes if compressed beyond a critical fraction of its radius. Let's wait it to reach its terminal speed $v_\infty \sim \sqrt{R}$. Hitting the ground, it will be compressed by an amount $x=v_\infty\sqrt{m/k} \sim R^2$. So the compression scales quadratically with radius, and small balls have more chances to "survive" the shock than big balls. 
A: One of the reason is the lack of "scale invariance", first noticed by Galileo in his "Two New Science". Galileo argued that animals cannot simply be scaled up, since their scaled bones would not support their scaled masses. For instance, an animal twice as wide, thick and tall, would be eight times heavier. Their bones would have to support eight times more weight. But their cross section is only four times larger. The scaled bone would not support the animal. 
Consider for instance a small monkey and a gorilla.  With some approximation we can consider them the same scaled animal.  Let us say the gorilla is twice taller, thicker and wider. Then the gorilla's bones would be only four times thicker than the small monkey's one. This means only four times more resistant. If both animals fall from the same height, in the same way, the impact force on the gorilla would be eight times larger. As long as their bones have similar composition (which I assume it's true) the gorilla's bones would break before.
Another example, given by Feynman: People make those incredible cathedral and castles out of matchsticks. But we don't see any scaled real building like those.
Of course this is not the complete story. From the biological viewpoint there must be other regards. I'm just doing what physicists do, simplifying as much as possible the problems to find some approximated answer.
