Yukihiro Fukuda / Japanese macaque (Macaca fuscata fuscata) mother with rare white furred male baby, Jigokudani Valley, Nagano Prefecture, Japan. June.

Charlie Summers / Lion (Panthera leo) ready to mount female, Ngorongoro Crater, Tanzania.

Doug Gimesy / Grey-headed Flying-fox (Pteropus poliocephalus) hangs from one foot from a branch. Yarra Bend Park, Kew, Victoria, Australia. December, 2017.

Andy Rouse / Indian Flying Fox , (Pteropus giganteus), roosting, India

Franco Banfi / Zebu bull, Bonito, Mato Grosso do Sul, Brazil

Staffan Widstrand / Wild Wonders of China / Portrait of a male Golden snub-nosed monkey (Rhinopithecus roxellana) Foping Nature Reserve, Shaanxi, China. Endangered species

Daniel Heuclin / Potto (Perodicticus potto) male in tree, Togo. Captive.

SCOTLAND: The Big Picture / Scottish wildcat (Felis silvestris grampia) male, on back to show underside for pelage scoring. Inside The Royal Zoological Society Scotland / RZSS mobile vet unit, Strathsprey, Cairngorms National P...

SCOTLAND: The Big Picture / Conservationist from The Royal Zoological Society Scotland / RZSS measuring the size of a Scottish wildcat's (Felis silvestris grampia) testes. Inside RZSS mobile vet unit, Strathsprey, Cairngorms Nat...

Luke Massey / Proboscis monkey (Nasalis larvatus), Tarakan, Indonesia

Luke Massey / Proboscis monkey (Nasalis larvatus) male, Tarakan, Indonesia

Anup Shah / Eastern chimpanzee (Pan troglodytes schweinfurtheii) male 'Faustino' aged 22 years, rear view showing testicles. Gombe National Park, Tanzania.