Frogs Are Irrational


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

2094 Frogs Are Irrational
Túngara frogs rely on voice, rather than looks, for sex appeal, but other voices can confuse. Credit: Brian Gratwicke via Wikimedia Commons

In news that might interest the newly single Miss Piggy, frogs have been observed to allow irrelevant factors to influence their mating choices. While similar behavioral traits have been demonstrated in humans, the finding shows how fundamental irrationality is to our psychology, exposing processes that rely on an assumption of rationality.

When offered the choice between two options, we can usually work out which one we prefer. Throw in a third option, inferior to either, and sometimes we end up picking second best, a product of what is known as the decoy effect. Graduate student Amanda Lea and Professor Michael Ryan of the University of Texas, Austin, found that the same applies in frogs.


The observation is a fundamental challenge to the notion of rational choice, since Lea and Ryan note, “Rational choices exhibit regularity, whereby the relative strength of preferences between options remains stable when additional options are presented.”

So far, Lea and Ryan’s work is only on female túngara frogs (Physalaemus pustulosus), so maybe it’s not that interesting to Miss Piggy, whose enthusiasm has only been established for male Hyalinobatrachium dianae frogs. However, psychologists may feel differently.

Female túngara frogs choose to mix their DNA with males that have the deepest and longest-lasting mating calls. There is a trade-off for the males, since such calls also attract predators, making the evolutionary balance a subject of interest to zoologists.

Previous studies have found that females are not 100% reliable at picking longer calls if the difference was a small proportion of the total length.


In Science, Lea and Ryan show that female choice gets even less reliable when a third frog joins the chorus. Thus, when choosing between frog A and the slightly more sustained frog B, females mostly chose contestant B. However, shorter calls from frog C confused the female, leading to them choosing frog A more often than they would in a head-to-head battle.

Lea and Ryan made the observation using 80 female túngaras, and confirmed it in a variety of circumstances, such as when the location of the decoy was clear, as well as when it was not. While some previous studies have been inconclusive, this is the first to clearly disprove regularity in animal mate choice.

Given the evolutionary benefits of picking the best mate, and the fact that competing calls would be something this species has plenty of experience tackling, it might seem surprising that the females could be fooled in this way.

The authors propose that in the midst of a frog chorus, thinking too hard about a decision can be as expensive as making the wrong one, either exposing oneself to predators or risking having some other frog snap up your man.


The decoy effect has been studied in humans for decisions such as buying goods and voting in crowded fields. Some pundits have even suggested political candidates can put the effect to use by encouraging weaker third parties.


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