Rational choice behavior in economics assumes that when given a choice, we will pick the one that maximizes benefits to us. However, there are things that can complicate this and cause us to pick less rationally. Now, let’s take these familiar, human concepts of economics and apply them to the ways that animals choose their food.
Hemingway et al. tested how the type of food Jamaican fruit bats chose to eat was impacted by the context it was given in. The context they changed was the presence of a decoy option – one that is less beneficial than any of the others. For the bats, the food options were ripe banana and ripe papaya, with unripe banana as the decoy. The ripe banana and papaya are both super tasty, have tons of nutrients, and are easy to eat. The unripe bananas are tougher to eat and not as nutritional as the ripe fruits, so they are less valuable to the bats. The presence of a decoy option like this can create preference where it otherwise wouldn’t exist. To put this situation into human perspective, Hemingway et al. gave the example of choosing between an all-inclusive vacation to Paris or Rome. Both of those are pretty amazing options, so people probably wouldn’t have a preference between them. However, when there’s a third option of a vacation to Rome without meals included, the all-inclusive Rome trip starts looking like the best choice, even if its value is the same as the Paris trip. The cause of this “irrational” preference comes from comparing options to others they are in context with instead of assessing their individual values.
Hemingway et al found this exact situation reflected in the fruit bats they studied – when there was only banana and papaya to choose from, the bats didn’t have a strong preference, but when they also had the unripe banana decoy they preferred banana 20% more! The bats are going against the constant-ratio rule of economics that assumes preferences between two options shouldn’t change when there is a third one present. The researchers used some pretty cool methods to figure this out. They captured all of the bats from the wild, being careful not to harm or distress them. Hemingway et al used an adorable method to make sure they could identify all the bats: they each got unique haircuts, and were given cute names like Beatrice and Fernando! Before putting the bats through the experiment, they had a training period so that they could learn how and where to get the food within the cage Hemingway et al had set up. They did this training in small groups over the course of two nights. When it was time for the experimental tests, bats were chosen in groups of two and alternated turns making their food choices. The tests lasted for one and a half hours each – three hours total per bat for the non-decoy and decoy trial. Since the bats were alternating turns, they had plenty of time to get hungry again between tests, so how much they ate in the first test wouldn’t affect the second. Other important things the researchers controlled for were the sex of the bats and the physical location of the different food options. They had half male and half female bats in their study, and they presented the same type of food at the same location it was in during training in each trial.
It is super cool that just like us humans, bats’ choices can be influenced by context, but there is still a lot we don’t know yet about this type of decision making. Similar behavior has been found in lots of other animals, like birds, fish, frogs, and even slime molds, but we are still learning about what causes it. Hemingway et al. propose that an animal’s diet may contribute to irrational decision making. This is because the behavior is seen in so many animals across different taxa, but not necessarily in closer relatives. For example, bees, hummingbirds, and the fruit eating bats from this study make context dependent choices in the presence of decoys, but frog eating bats don’t. The two types of bats are more closely related to each other than the bees or hummingbirds, but the fruit eating bat, hummingbird, and bee all have similar sugary diets. One big question that can still be explored is whether animals make irrational decisions across the board, or just in certain areas. If an animal’s choices in food are affected by decoys, would their choices in mates or habitats be too?
It is interesting to learn more about how animals think and make decisions. And perhaps even more amazing is finding similarities between animal and human behaviors. The Jamaican fruit bats studied by Hemingway et al give an opportunity for both, which makes this research so special. However, as is a common theme in the entire field of science, answering one question has led us to many more new and exciting ones to investigate in the future.
References:
- Hemingway et al. (2021) Context-dependent preferences in wild fruit bats. Animal Behaviour 179, 65-72 https://doi.org/10.1016/j.anbehav.2021.06.016
