Female gray tree frogs choose mates less reliably as competing calls multiply in a lab test

The playback schedule is what makes this experiment worth reading. In a pond, calls overlap, and overlapping signals make it harder to pick one out of the noise, a problem known as energetic masking ^[7]. Biologists have long seen female preferences weaken in choruses and have usually blamed masking ^[8]. The team took it out of play by running every recording in sequence, so no two calls ever overlapped ^[6]. Each call reached the female clean, and her choices still degraded as calls were added ^[5].

I think the design settles its narrow question. With overlap gone, the authors place the limit in the female's own cognition ^[17]. "The challenge comes from too many males to choose from, not being unable to hear the males clearly," one of them wrote in The Conversation ^[9].

Across the three set-ups a female faced two, four or eight speakers ^[1]. A frog hopping at random would reach the target half the time in the smallest set-up and one time in eight in the largest ^[2]. A female whose preference held firm would pick the target every time, whatever the number of speakers. So the useful measure is how far the frogs slid toward the chance floor. The Conversation account reports the direction of each effect. It does not report the proportions or decision times ^[5].

The lab test cannot show who mates in a real pond. Besides capping the options, the arena removed vegetation and predator risk ^[12]. In a natural chorus, sensory and cognitive limits probably act together, and the authors say their next step is to measure how much overload matters there ^[14]. They want to know whether decisions really take longer in the wild and whether females end up with less preferable males ^[14]. Until then, the claim that chorus density changes which males mate rests on a lab preference test ^[14]. So does the authors' suggestion that males could exploit the limit ^[11].

Other animals show the same pattern. Bees choosing among flowers, ants comparing nest sites and mosquitoes picking egg-laying sites all decide worse as options multiply, according to the authors ^[15].