Morley Read / Slow motion clip of a group of male Mallards (Anas platyrhynchos) competing violently to mate with a single female, Cornwall, England, UK, May 2018. (non-ex)

Alex Mustard / Yellowtail tang (Zebrasoma xanthurum) male and female turn belly to belly during spawning to ensure fertilization. Temple, Ras Umm Sid, Sharm El Sheikh, Sinai, Egypt. Red Sea. This action is very fast...

John Cancalosi / Sonoran desert toad (Incilius alvarius) pair mating, with trail of spawn in water. Arizona, USA.

Tony Wu / Humphead parrotfish (Bolbometopon muricatum) shoal spawning in early morning, part of mass aggregation of thousands of fish. Caroline Islands, Palau.

David Tipling / Common European adder (Vipera berus) two males fighting over a female. Holt, North Norfolk, England, UK. April

David Tipling / Common European adder (Vipera berus) two males fighting over a female, Holt, North Norfolk, England, UK. April

David Tipling / Common European adder (Vipera berus) two males fighting over a female, Holt, North Norfolk, England, UK. April.

Oscar Dewhurst / Red deer (Cervus elaphus) stag roaring, silhouetted under trees at sunrise. Bushy Park, London, UK. September

Alex Mustard / Pair of Western clown anemonefish (Amphiprion ocellaris) spawning orange eggs on the rock beneath their Magnificent sea anemone (Heteractis magnifica) home on a coral reef. This photo shows the larger...

John Chan / Crenulated fiddler crab (Uca crenulata) waving its major claw at another crab, part of a courtship display, Southern California, USA, June.

John Shaw / Great frigatebird (Fregata minor) male at nest site, with gular sac inflated to attract females. Genovesa Island, Galapagos, May.

John Shaw / Black-browed albatross pair (Thalassarche melanophris) mutual grooming during copulation. New Island, Falkland Islands, November.