why are some animals so… jerky?


like, birds. they move in sharp bursts. and squirrels. why do they do this and other animals, like bears, don’t?

In: Biology

Because they are small, and staying still for too long or moving too slowly could mean the difference between life or death


The short answers is: they can.

Moving fast requires two things, ability to contract muscles fast and not hurting yourself in the process.

Larger the animal higher the mass the body parts have, if you were to contract your muscle at a speed humming bird contracts it’s, you woul tear your muscles or tendons, because to force required is so much higher due to higher mass.

This ratio scales especially badly, since the the relationship between size and mass is approximately a cube. Ie if you are twice as big you will weigh 8 times as much.

Small animals do this because they are much stronger relative to their weight than large animals. As a rough approximation, strength goes up with the square of your size. This is because the muscle strength is proportional to the muscle cross section area. Think about how many muscle fibers of a the same thickness you can fit in an animals neck as it gets bigger. The diameter of the neck makes it stronger but the length doesn’t. But mass goes up with the cube of the animal’s size. Think about how all the formulas for volume usually have a cube in them. So as you get larger, mass goes up faster than strength. This is why small animals can accelerate their movements faster than large animals.