Some Bats, Like People, Make Irrational Food Choices

It's that third 'decoy' option that confuses them.

Two fruit bats about to rest after a busy night feeding.
Two fruit bats after a night of feeding. / Getty Images

Humans often make irrational choices when shopping for food. Sometimes that’s because it can be confusing choosing between prices and sizes. 

One well-known marketing trick is known as the decoy effect. If there’s a small cup of coffee for $3 or a large cup of coffee for $5, you might choose the small cup. But if they add a third medium “decoy” cup and it’s $4.50, you might opt for the larger cup at $5 because you think you’re getting a much better deal.

But it’s not just people who are fooled by an additional option. A new study with bats finds that when given three alternatives, bats will also make irrational food choices.

“Irrational choices are so common in human decision-making that they have prompted researchers to explore them in other, non-human animals. Studies so far have almost exclusively shown evidence for irrational behavior,” lead author Claire Hemingway, who recently received her doctorate from the University of Texas, tells Treehugger.

“These studies have tested food preferences, but also mating preferences, and habitat preferences, and have been conducted over really broad taxonomic groups including slime molds, fish, frogs, birds, and mice.”

Hemingway earlier explored food decision-making in frog-eating bats (Trachops cirrhosus).

“These bats are often choosing between many calling frogs, they are trying to maximize several aspects of their choice, and they are making these decisions rapidly, all of which are conditions in which we humans tend to switch from making rational choices to making irrational ones,” Hemingway explains.

Most of her research found that frog-eating bats are good at making rational decisions, even when their choices get complicated. So she took things a step further to find out if there was something specific in their diet that impacted their smart choices or it was the bats themselves.

For the new study, she opted to test the decision-making abilities of a close relative with a different diet. This time around she worked with Jamaican fruit bats (Artibeus jamaicensis).

The results were published in the journal Animal Behaviour.

Bats and Bananas

Hemingway caught bats in mist nets then organized them into groups of three or four in flight cages because Jamaican fruit bats don’t like to eat by themselves. Once they were used to their new surroundings, she took them out one at a time so they wouldn’t be influenced by the other animals.

First, she gave them a choice between a ripe banana and ripe papaya and they didn’t prefer one over the other. Then she added a decoy option of an unripe banana. With the third choice, the bats almost always chose the ripe banana.

“Because decoy effects are so common, I was less surprised that they were occurring than I was by how strong the effects appeared to be,” Hemingway says. “The relative preferences between the two preferred options changed quite dramatically upon the introduction of the decoy.”

This was different from the frog-eating bats she had studied earlier which weren’t influenced by dietary decoys she introduced into the study and always made rational decisions about what foods to eat.

Hemingway says she can only speculate about why the two species reacted differently when the decoy option was added.

“Because other animals that have more similar diets to the fruit bats, such as hummingbirds and bees, exhibit similar irrational behaviors, it seems very likely that diet may play some role in shaping these behaviors,” she says.

“For fruit bats, hummingbirds, and bees, their food is advertising itself to the animal and is very nutrient-rich, both of which may reduce the costs of imperfect decisions. For frog-eating bats, frogs are actively evading them and at any given time may be far less abundant than fruit, which may mean that making suboptimal decisions comes at a higher price.”

Learning about the food-related decisions animals make is helpful for researchers studying those species. But it may also offer broader assistance to other scientists.

“By studying these behaviors outside of humans, we can begin to understand just how common they are across the animal kingdom, but we can also begin to explore which conditions are likely to produce such behaviors,” Hemingway says.

“In humans, it is commonly understood that we often make irrational decisions. By identifying the factors that contribute to these irrational behaviors broadly across different taxonomic groups, we can better understand our own limitations in making decisions.”

View Article Sources
  1. Hashem, Tareq, and Mohammad Fahmi Alzyoud. "Influence of Decoy Marketing on Impulsive Purchasing Behavior Among Adult Customers of Tech Market in Jordan, Mediating Role of Brand Equity." Journal of Critical Reviews, vol. 7, no. 15, 2020, pp. 3729-3742.

  2. Hemingway, Claire T., et al. "Context-Dependent Preferences in Wild Fruit Bats." Animal Behaviour, vol. 179, 2021, pp. 65-72., doi:10.1016/j.anbehav.2021.06.016

  3. lead author Claire Hemingway, who recently received her doctorate from the University of Texas

  4. "What Happens when Bats are Given Three Choices?" EurekAlert, 2021.