My, what a large vocal sac you have! The flexible membrane of skin possessed by most male frogs is the instrument by which their mating calls are amplified, alerting she-frogs of their availability and at the same time, filling the wilds with their wonderful song. This Upper Amazon treefrog (Dendropsophus bifurcus) – photographed by Andreas Kay at the Reserva Ecológica Tamandua in Ecuador – is clearly no slouch in the vocal sac department. Female frogs, are you listening?
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