Danny Green / Red deer stag (Cervus elaphus) roaring. Bradgate Park, Leicestershire, UK, October.

Ole Jorgen Liodden / Hippopotamus (Hippopotamus amphibius) rearing head out of water, creating spray, Lake Naivasha, Kenya.

Klein & Hubert / Red deer (Cervus elaphus) stag calling in snowy mountains forest, portrait, Germany

Eric Dragesco / Wild female Snow Leopard (Panthera uncia) portrait, standing camouflaged on rocky mountainside, at an altitude of 2500m, Altai mountains, Mongolia. July . NB-This female probably has cubs: the fur aro...

Edwin Giesbers / RF- African Lion (Panthera leo) head portrait of male roaring, captive. (This image may be licensed either as rights managed or royalty free.)

Loic Poidevin / Red deer (Cervus elaphus) male bellowing near female, Chambord National Park, France, September.

Mateusz Piesiak / Red deer (Cervus elaphus) in the pine forest bellowing during the rutting season. Barycz Valley Landscape Park, Poland. September.

Mark MacEwen / Southern elephant seal (Mirounga leonina) beach master / bull roaring, portrait. St Andrews Bay, South Georgia. October.

Mark MacEwen / Southern elephant seal (Mirounga leonina) beach master / bull roaring, mountain in background. St Andrews Bay, South Georgia. October.

Mark MacEwen / Southern elephant seal (Mirounga leonina) beach master / bull roaring alongside females in breeding colony. St Andrews Bay, South Georgia. October 2017.

Mark MacEwen / Southern elephant seal (Mirounga leonina) beach master / bull roaring. St Andrews Bay, South Georgia. October.

Mark MacEwen / Southern elephant seal (Mirounga leonina) beach master bull and pup roaring in breeding colony. St Andrews Bay, South Georgia. October.

Oscar Dewhurst / Red deer (Cervus elaphus) stag roaring in grassland. Richmond Park, London, England, UK. October

Fabrice Cahez / Red deer (Cervus elaphus) stag bellowing with vegetation in antlers, Vosges, France, September

Fabrice Cahez / Red deer (Cervus elaphus) stag bellowing, Vosges, France, September

Guy Edwardes / Red deer (Cervus elaphus) stag calling in grassland. Bushy Park, London, England, UK. October.

Guy Edwardes / Red deer (Cervus elaphus) stag roaring during rut, silhouetted in grassland. Bushy Park, London, England, UK. October.

Edwin Giesbers / RF - Red deer (Cervus elaphus) Richmond Park, London, England, UK. (This image may be licensed either as rights managed or royalty free.)

Edwin Giesbers / RF - Red deer (Cervus elaphus) Richmond Park, London, England, UK. (This image may be licensed either as rights managed or royalty free.)

Edwin Giesbers / Red deer (Cervus elaphus) bellowing, Richmond Park, London, England, UK. October.

Edwin Giesbers / Red deer (Cervus elaphus) stag bellowing during rut at dawn, Richmond Park, London, England, UK.

Danny Green / Red Deer Stag (Cervus elaphus) roaring at dawn. Bradgate Park, Leicestershire, UK, October.

Edwin Giesbers / Red deer (Cervus elaphus) silhouetted stag bellowing during rut in grassland, doe in background. Richmond Park, London, England, UK. October

Andy Rouse / Bengal tiger (Panthera tigris) with mouth open, cooling in pool during summer heat. Ranthambhore National Park, India.

Oscar Dewhurst / Red Deer (Cervus elaphus) stag roaring silhouetted in grassland at sunrise. Richmond Park, London. September

Oscar Dewhurst / Red deer (Cervus elaphus) stag silhouetted, roaring in the mist before sunrise. Richmond Park, London. September

Oscar Dewhurst / Red deer (Cervus elaphus) stag roaring in the mist, silhouetted, backlit at sunrise. Richmond Park, London, UK. October

Oscar Dewhurst / Red deer (Cervus elaphus) stag roaring with bracken-covered antlers. Richmond Park, London, UK. October

Oscar Dewhurst / Red deer (Cervus elaphus) stag in misty conditions bellowing whilst sat down in long grass with the rising sun in the background. Richmond Park, London, UK. September

Kerstin Hinze / Red deer (Cervus elaphus) stag licking its nose and yawning during rut, September. Captive.

Philippe Clement / Red deer (Cervus elaphus) stag bellowing amongst females during the rut, Jaegersborg, Dyrehaven, Denmark, September.

Philippe Clement / Red deer (Cervus elaphus) stag trying to mount a female during the rut, Jaegersborg, Dyrehaven, Denmark, September

Philippe Clement / Red deer (Cervus elaphus) stag bellowing at a rival male during the rut, Jaegersborg, Dyrehaven, Denmark, September.

Juan Carlos Munoz / Red deer (Cervus elaphus) stag bellowing in Cork oak forest, Sierra de San Pedro, Extremadura, Spain, September.

David Tipling / Red deer (Cervus elaphus) stag bellowing at dawn during rut Bushy Park London, England, UK. October

David Tipling / Red deer (Cervus elaphus) stag bellowing at dawn during rut Bushy Park London, England, UK. October

Sylvain Cordier / RF - Grizzly bear (Ursus arctos horribilis), roaring, Utah, USA. Captive. (This image may be licensed either as rights managed or royalty free.)

Fabrice Cahez / Red deer (Cervus elaphus) stag roaring, with hinds nearby amongst forest trees, Vosges, France, September.

Fabrice Cahez / Red deer, (Cervus elaphus) stag roaring in forest, Vosges, France, September.

Bruno D'Amicis / Silhouette of Red deer (Cervus elaphus) stag bellowing during the rut. Central Apennines, Abruzzo, Italy, October.

Bruno D'Amicis / Red deer (Cervus elaphus) stag bellowing during the rut. Central Apennines, Abruzzo, Italy, October.

Bruno D'Amicis / Red deer (Cervus elaphus) stag bellowing during the rut. Central Apennines, Abruzzo, Italy, October.

Bruno D'Amicis / Red deer (Cervus elaphus) stag bellowing during the rut. Central Apennines, Abruzzo, Italy, September.

Bruno D'Amicis / Red deer (Cervus elaphus) stag bellowing during the rut. Central Apennines, Abruzzo, Italy, September.

Will Watson / Red Deer (Cervus elaphus) bellowing, Richmond Park, London, UK.

John Cancalosi / Red deer (Cervus elaphus) stag roaring during rut, with resting females, England, UK. September.

Edwin Giesbers / Red deer (Cervus elaphus) stag bellowing during rut, Richmond Park, London, England, UK. October.

Edwin Giesbers / Red deer (Cervus elaphus) stag bellowing during rut, Richmond Park, London, England, UK. October.