To Not Get Caught by a Predator

By Noah Bressman

If you are going for a walk and encounter a hungry lion a few feet in front of you, you would probably run away immediately. However, if you were watching that lion from a mile away through binoculars, you probably would not be scared for your life, just enjoying a safari. Now, what if that lion started running right at you? Would you flee immediately, even though it is a mile away? Or would you flee as it approaches closer, and if so, at what distance would you respond and escape? Do you think you would respond differently if you saw the lion head-on than if you saw it out of the corner of your eye, or if the lion was not moving directly at you?

How you respond can be a matter of life or death, and this decision needs to be made in an instant. With so little time, how do you make the best decision for your safety using only the limited information from your eyes? Replace the lion with a projector and yourself with a zebrafish, and you have the set-up used by scientists at the University of California, Irvine, to answer the above questions.

A looming stimulus can be simulated on a screen or a projector by increasing the size of a circle, which simulates a predator coming closer and closer being viewed at a wider and wider angle. Image modified from Amberle McKee’s figures.

In a recent Integrative Organismal Biology paper, a group led by Amberle McKee wanted to see how the angle at which prey see a predator approaching and the speed at which that angle changes affects the strategy the prey uses to safely escape. McKee used a looming stimulus – a projected circle or image that increases in size to simulate an approaching predator. As the circle got bigger, McKee and her team kept track of the angle of the eyes in relation to the expanding circle. McKee found a threshold visual angle between the fish’s eye and the edges of the circle that would cause the zebrafish to dart away in a short burst with a strong flick of its tail. However, would a zebrafish respond in the same way to a circle as it would to a predator?

As a matter of fact, yes! McKee replaced the looming stimulus simulation with an actual predator (a red Texas cichlid) and found the same result. If this was not compelling enough, McKee and her team created mathematical models of similar predator-prey interactions, which also told the same story. These models also predicted that based on the zebrafish’s threshold visual angle, it can evade predators up to twice as fast as it using its escape strategy.

Zebrafish (Danio rerio). Photo by Shaun Hughes.

This research helps shed light on how prey detect threats, process that information, and respond. While it may seem like you can respond to things you see instantaneously, there is actually a slight delay as it takes time for information to go from the eyes to the brain, which then needs to make a decision on how to act, sending that decision down through the nerves to the muscles to create a response. McKee and her team showed that predator avoidance is not simply a matter of seeing the predator and how close it gets, but involves factoring the angle of approach – among other factors – to maximize survival chances.

While McKee’s findings may help you calculate the best response to avoid getting eaten by the aforementioned approaching lion, you probably should not waste too much time thinking about your response and just follow your survival instincts.


Dr. Noah Bressman is a Postdoctoral Fellow at Chapman University, studying fish biology, biomechanics, biomaterials and behavior. You can find more at or @NoahwithFish, or contact him at

One comment

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s