Guy Edwardes / Marsh Frog (Pelophylax ridibundus) vocalising with bokeh effect in the background, Danube Wetlands, Bulgaria

Guy Edwardes / Marsh Frog (Pelophylax ridibundus) vocalising with bokeh effect in the background, Danube Wetlands, Bulgaria

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

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

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

Yashpal Rathore / Jayarami Bush frog (Raorchestes jayarami), inflating vocal sac, calling to attract mate, Endemic to Western Ghats. Anamalai Wildlife Sanctuary, India.

Alex Hyde / Hourglass treefrog (Dendropsophus ebraccatus) male with inflated vocal sac calling at night, Central Caribbean foothills, Costa Rica

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

Rolf Nussbaumer / Couch's Spadefoot (Scaphiopus couchii) adult at night calling with vocal sac inflated. Laredo, Webb County, South Texas, USA, April.

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

Wild Wonders of Europe / Schandy / European green toad (Bufo viridis) calling, vocal sac inflated, in a pond (at 2,711m) Adylsu valley, side valley to Baksan valley and Elbrus, Caucasus, Russia, June 2008

Wild Wonders of Europe / Schandy / European green toad (Bufo viridis) calling, vocal sac inflated, with eyes closed, in a pond (at 2,711m) Adylsu valley, side valley to Baksan valley and Elbrus, Caucasus, Russia, June 2008