ELi5: Why do small animals (birds, squirrels, etc.) have such “faster reflexes” than humans?



I understand they are smaller and can move faster than humans, but why can they wait so long before moving?

For instance, when you’re driving and a bird is able to wait until the absolutely last second before flying away and avoiding getting hit. What allows animals to have such better reflexes?

In: Biology

Birds sit there and almost get hit because they’re actually pretty bad at gauging the speed of an incoming object. They don’t really understand that your car is moving faster than anything in nature could ever move.

They instinctively fly away when something gets too close, but for a speeding hunk of metal that range is much too small and many definitely do get hit by cars.

More generally, small animals can have very quick twitch behavior because they have such little mass to accelerate. You’re a muscle and bone battleship compared to a sparrow, you’re not stopping on a dime.

Regarding birds they can process images from their eyes much faster than us humans. Essentially they can see “faster” which means they can more accurately estimate speeds and positions of things in their surrounding. So from the birds perspective they move out of the way with some margin as to them the car doesn’t appear as close to hitting them as we perceive.

Regarding reflexes in general they are automatic responses and triggered by a nerve signal being sent to the brain and spinal cord. The reflex happens when the signal is instantly sent back from the spinal cord with instructions to do something. For example if you place your hand on a hot stove you will pull away your hand as a reflex. After a second or two you will feel the pain.

The delayed pain response is because it takes longer time for the signal to travel to the brain and be intepreted than it takes for it to travel to the spinal cord and back to the muscle.

Smaller animals have a shorter distance from their muscles to their spinal cord and brain (since they have smaller bodies). Thus it takes less time for the signal to travel in the body of a squirrel than in our body. Thus they have quicker reflexes than we do.


Muscles come in two big varieties: fast-twitch and slow-twitch.

Fast twitch muscles react quickly, but tire easily. Your housecat is a great example of an animal with lots of fast-twitch muscles. Their physiology is designed for waiting for prey, then pouncing on it before it knows what’s happening. If you’ve ever had a heavy play session with a cat though, you’ll notice they start panting and get tired *quick*.

Humans are endurance hunters. We are basically the Terminators of the animal kingdom. We can run for miles chasing prey seemingly unphased until the prey gets tired. See this [BBC Earth video](https://www.youtube.com/watch?v=826HMLoiE_o). We have slow-twitch muscles that react slowly, but can go on *forever* from the perspective of a cat, antelope, or deer.

So, why do these animals seem to move quicker? Because they are prey and need to be able to boogie when the time comes, hopefully outrunning their predators by outlasting them (antelope vs cheetah) or just getting away quicker to the point they give up (antelope vs human)

In respect to cars v birds & insects, doesn’t or wouldn’t the air flowing in front and over a moving car effectively pull the animal/insect through a ‘slip stream’? Maybe they don’t fly around at all..

According to this article, metabolic rates are another factor that changes perception of time/ reflexes. So the faster a creature’s metabolic rate, the slower that they perceive time, leading to faster reaction speeds.


the smaller an animal the “slower” time feels for them relative to humans. A Giant moving his legs would also seem slow if observed by a human but for the giant itself it feels normal. If u try to catch a fly imagine that for the fly’s perception a very slow arm is approaching them. Ofcourse there are no giants and the fly might benefit also from other ressources to avoid getting smushed.