David Perpinan / Male Mediterranean tree frog (Hyla meridionalis) calling, showing vocal sac inflating, Barcelona, Spain, May. Filmed at night with an infrared camera.

Konrad Wothe / Three-striped poison frog (Ameerega trivittata) croaking, Panguana Reserve, Huanuco Region, Peru.

Ingo Arndt / Natterjack toad male calling {Bufo calamita} vocal sac inflated, Germany

Sean Crane / Red-eyed Tree Frog (Agalychnis callidryas) calling, Tortuguero National Park, Costa Rica

Thomas Marent / European Tree Frog (Hyla arborea) calling, Switzerland

Scott Leslie / American Toad (Bufo americanus) calling in spring pond, West Stoney Lake, Nova Scotia, Canada. Sequence 1 of 2

Konrad Wothe / Edible Frog (Rana esculenta) croaking, Germany

Konrad Wothe / Edible Frog (Rana esculenta) croaking in pond, Germany

Martin Gabriel / Mediterranean tree frog vocalising {Hyla meridionalis} Luberon, France, Europe

Doug Wechsler / Long fingered slender toad {Ansonia longidigita} male vocalising. Borneo , Bentuang-karimun, Indonesia

David Perpinan / Male Mediterranean tree frog (Hyla meridionalis) calling, showing vocal sac inflating, Barcelona, Spain, May. Filmed at night with an infrared camera.

David Perpinan / Male Mediterranean tree frog (Hyla meridionalis) calling, showing vocal sac inflating, Barcelona, Spain, May. Filmed at night with an infrared camera.