Túngara Frog

Because the payoff in mating success is large enough to be worth the risk. A female túngara frog strongly prefers a call that ends in chuck notes over a plain whine, and prefers more chucks to fewer, so a male who adds them wins far more matings. The cost is that fringe-lipped bats (Trachops cirrhosus) and frog-biting midges also use the chuck notes to locate the caller, and a chucking male is much more likely to be caught by a bat or bled by midges than a male giving only whines. Males manage the trade-off dynamically — they call more elaborately when other males are calling nearby (safety in numbers, and more competition for mates) and drop back to simple whines when alone or when a bat has just passed.

It is a floating raft of whipped mucus that protects the eggs. During mating, the female releases a fluid along with her eggs, and the pair — with the male clasped on her back — kick and beat this fluid with their hind legs into a stiff white foam, roughly the size of a large biscuit, floating on the surface of a puddle or pond. Between about 100 and 250 fertilised eggs are suspended inside it. The foam keeps the eggs moist if the water level drops, buffers them against temperature swings and sunlight, contains antimicrobial compounds that resist bacteria and fungi, and hides them from many predators. After a few days the tadpoles hatch and wriggle down out of the foam into the water below.

It has become a textbook example of how animals — and brains in general — make comparative decisions, because researchers can play synthetic calls to females in the lab and see exactly which they choose. Females show consistent preferences (chucks over no chucks, lower-pitched chucks that indicate a bigger male, calls that start sooner). They also show quirks familiar from human psychology — a female's choice between two males can be flipped by adding a third, worse option — an "irrational" decoy effect — showing that she is not scoring each male on an absolute scale but comparing them against each other. This work has made the little frog important far beyond herpetology.

Not at all — it is one of the most abundant and resilient frogs in the American tropics. It is listed as Least Concern with a stable population, it occupies a huge range from Mexico to northern South America, and it does especially well in habitats people have disturbed. It will breed in cattle hoofprints, roadside ditches, drainage channels, discarded containers, and tyre ruts — any small pool of standing water that lasts a week or two. This flexibility, its short generation time, and its high reproductive output make it secure even as many other tropical amphibians decline.