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Scoping Science: How Do Animals Look for Food?

An eagle-eyed activity from Scientific American

George Retseck

Key Concepts
Visual search
Search image

You probably have food preferences—perhaps you love salty snacks or detest red meat—but in general, humans eat many different foods. For that reason, our species is considered omnivorous. But some animals are much more choosy. Herbivorous rabbits, for example, dine only on plants whereas carnivores, such as sharks, feast principally on animal prey.

Locating these very different types of foods can obviously require different tactics. In this activity, you'll learn about a theory that biologists use to explain different strategies for foraging, or finding food. You'll also apply this theory to test your visual hunting skills.

Believe it or not, animals don't just pursue the first food option they see. Biologists who study animal behavior have found that different species have different strategies. This is because locating a meal isn't always easy—it requires time and energy. To maximize the amount of energy an animal gets from its prey, it needs to pursue food nutritious enough to make up for the time and energy it needs to catch and consume a meal.

Scientists call this "optimal foraging theory"—or the best strategy for finding a meal—and they have a simple mathematical formula to express it: E/h + s. E stands for energy, specifically the energy an animal gains from eating food. The h stands for handling time—this represents how long it takes to get the food ready to eat. An apple, for example, has very little handling time, but an oyster requires more effort. The s is for search time, which can vary depending whether food is rare or plentiful, or when food is hard to detect or sticks out easily. Strategies shift based on an animal's abilities and environment. In this activity you'll measure search times and experience one aspect of optimal foraging theory firsthand.

•    Where's Waldo? or other visual search book (you can find these books at your local library)
•    Pencils and paper
•    A partner (groups of two or three individuals also work)
•    A clock or stopwatch

•    This activity works best with a visual search book such as Where's Waldo? in which you repeatedly seek out a specific target.
•    To make the activity more challenging, do not peek at the puzzles before it is your turn to "hunt."
•    Ask a partner to be the first hunter. Ask him or her to not peek at the image search until you say, "Go!"
•    Tell the "hunter" what target or "prey" he or she will seek out in multiple puzzles (Waldo, for example, is a good target).

•    Record the "hunter's" name and his or her target prey.
•    Hit the stopwatch or start watching the clock when you say, "Go!" Time how long it takes your partner to find his or her prey and record the total time needed. Are you surprised by how quickly or slowly your partner found the target?
•    Switch roles with your partner and repeat the previous steps. Was finding your target easier or harder than you expected? What made the task challenging?
•    Switch back and forth until you have each "hunted" your prey at least five times. Every time it is your turn, try a different puzzle page but seek out the same target. Does changing environments make the puzzles easier or more difficult? Do you think you get better at finding the same target in different environments?
•    So far, you have been hunting as a specialist—you have just one kind of prey. Start the activity again and repeat as a generalist, meaning you can hunt different kinds of prey. In this version, pick a different target every time you hunt, but once again use a new puzzle page each time. Repeat five times each and record your times. Do you notice any differences as a generalist than a specialist?
•    Extra: If you want to compare one more variation, try hunting for a totally different target in puzzle pages you have already seen. Is it easier to hunt in "familiar territory"?
•    Next, look at your times as both a generalist and as a specialist. Did either your or your partner's hunting skills improve? Did times increase or decrease as you repeated the search?
•    Foraging theory suggests you need to select foods that give you enough energy to make up for that which you lose in the time spent hunting and catching food. Which prey items took the most time to find? Following the theory's logic, what would make hunting these items worthwhile?
•    Extra: Because you've mostly played this activity with time in mind, create your own variation that tests another component of optimal foraging theory: energy. With your partner, decide on different energy values for different targets, then revisit old puzzle pages and give each other 10 minutes to collect as many prey items as they can find. In this version, each hunter needs to declare what he or she is searching for and can only collect points by finding a mentioned target. How do you and your partner match up? Are there strategies that work in your favor, such as seeking out targets with a certain value?

Observations and results
Did seeking the same target as a specialist get easier over time compared with seeking new targets in each puzzle?

In this activity, your visual search was very similar to that used by a hunting hawk as it soars high above the ground. As you probably noticed, trying to identify your target in such a cluttered landscape was not easy. Yet, you may have also found that by searching for the same target repeatedly, you became more adept at looking for that particular kind of prey. This is a common result and something that scientists have discovered in birds of prey. Biologists call this trick developing a "search image," because it allows the animal to have a very specific visual image in mind when scanning a landscape. Changing your target every time, however, is more taxing on your brain and makes a long search even longer.

More to explore
Optimal Foraging Game from the University of Toronto
Optimal Foraging Theory—an avian perspective from The Wild Classroom
Where's Waldo? puzzles online from
The Brains behind Where's Waldo? from Science Buddies
Online Search Games from

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