Marie Read / Black-necked stilts (Himantopus mexicanus) pair performing post-copulatory display (as copulation ends, the male slides off the female leaving his wings draped over her and crossing his bill with hers...

Miles Barton / Panamanian golden frog (Atelopus ziteki) reacting to the image of a frog on a video monitor. Experiment carried out to reveal the purpose of the frog's waving behaviour - to attract mates and deter ri...

Solvin Zankl / Mating swarm of Long-tailed / Tisza mayflies (Palingenia longicauda) Tisza river, Hungary, Every female is approached by several mature males. Eventually the female mates with one of them on the water...

Solvin Zankl / Mating swarm of Long-tailed / Tisza mayfly(Palingenia longicauda) Every female is approached by several mature males. Eventually the female mates with one of them on the water surface. June 2008

Solvin Zankl / Female Long-tailed / Tisza mayfly (Palingani a longicauda) rise up in the air soon after mating, where they form huge swarms and are out of range from males still searching for mates close to the wate...

Solvin Zankl / Female Long-tailed / Tisza mayfly (Palingani a longicauda) rise up in the air soon after mating, where they form huge swarms and are out of range from males still searching for mates close to the wate...

Stefan Christmann / Emperor penguin (Aptenodytes forsteri), three in fight over mates at start of breeding season. Atka Bay, Antarctica. May.

Alex Mustard / Day octopus (Octopus cyanea) darker male reaching over and mates with a lighter female on the wreck of a barge. Gubal Island, Egypt. Strait of Gubal, Gulf of Suez, Red Sea.

Nick Upton / Male Yellow dung flies (Scathophaga stercoraria) competing for mates on sheep dung, trying to knock and wrestle other males off the backs of the females they are guarding, Wiltshire, England, UK, Marc...

Nick Upton / Male Yellow dung flies (Scathophaga stercoraria) competing for mates on sheep dung, trying to knock and wrestle other males off the backs of the females they are guarding, Wiltshire, England, UK, Marc...

Nick Upton / Male Yellow dung flies (Scathophaga stercoraria) competing for mates on sheep dung, trying to knock and wrestle other males off the backs of the females they are guarding, Wiltshire, England, UK, Marc...

Alex Mustard / Spinner dolphins (Stenella longirostris) female mates with a male below, while another male accompanies. The two males were taking it in turn to mate with her. Sataya Reef, Fury Shoal, Egypt. Red Sea

Jose B. Ruiz / Shepherds painting red onto underside of male sheep. When he mates with a female she will have a red mark on her fleece, showing that she has been mated. Torres del Paine. Patagonia, Puerto Natales, C...

Marie Read / Black-necked sStilt (Himantopus mexicanus) pair building nest in shallow wetland: male in foreground is squatting and pushing backwards with his feet/legs to form a nest scrape in vegetation the pair...

Marie Read / Black-necked Stilt (Himantopus mexicanus) pair building nest in shallow wetland, male in foreground in squatting and pushing backwards with his feet/legs to form a nest scrape in vegetation the pair...

Marie Read / American avocet (Recurvirostra americana) pair performing post-copulatory display (as copulation ends, the male slides off the female leaving his wings draped over her and crossing his bill with hers,...

Marie Read / American Avocet (Recurvirostra americana), pair copulating, Bear River Migratory Bird Refuge, Utah, USA, May.

Marie Read / Northern cardinal (Cardinalis cardinalis) male (right) feeding his mate in spring as part of courtship/pair formation, termed "allofeeding", New York, USA, May.

Marie Read / Northern cardinal (Cardinalis cardinalis) male (right) feeding his mate in spring as part of courtship/pair formation, termed "allofeeding", New York, USA, May.

Marie Read / Northern cardinal (Cardinalis cardinalis) male (right) feeding his mate in spring as part of courtship/pair formation, termed "allofeeding", New York, USA, May.

Tui De Roy / Adelie penguin (Pygoscelis adeliae) fighting over mates and nest sites, Prydz Bay, near Davis Station, Vestfold Hills, Ingrid Christensen Coast, East Antarctica, November.

Tui De Roy / Adelie penguins (Pygoscelis adeliae) fighting over mates and nest sites, Prydz Bay, near Davis Station, Vestfold Hills, Ingrid Christensen Coast, East Antarctica, November.

Tui De Roy / Adelie penguin (Pygoscelis adeliae) fighting over mates and nest sites, Prydz Bay, near Davis Station, Vestfold Hills, Ingrid Christensen Coast, East Antarctica, November.

Tui De Roy / Adelie penguin (Pygoscelis adeliae) fighting over mates and nest sites, Prydz Bay, near Davis Station, Vestfold Hills, Ingrid Christensen Coast, East Antarctica, November.

Nick Upton / Male White admiral butterfly (Limenitis camilla) standing on sunlit leaves, guarding its territory and looking out for mates, Woodland edge, Wiltshire, UK, July.

Georgette Douwma / Golden butterflyfish (Chaetodon semilarvatus) with Fire coral (Millepora dichotoma) this species is one of the few fish species to have longterm mates. Egypt, Red Sea.

Georgette Douwma / Golden butterflyfish (Chaetodon semilarvatus) with a Bluestreak cleaner wrasse (Labroides dimidiatus) this species is one of the few fish species to have longterm mates. Egypt, Red Sea.

Georgette Douwma / Golden butterflyfish (Chaetodon semilarvatus) with Fire coral (Millepora dichotoma) this species is one of the few fish species to have longterm mates. Egypt, Red Sea.

Denis-Huot / Lion (Panthera leo) male biting female as he mates with her and she tries to escape, Masai mara, Kenya. Vulnerable species.

Denis-Huot / Lion (Panthera leo) biting female as he mates with her, Masai-Mara Game Reserve, Kenya. Vulnerable species.

Danny Green / Tiger (Panthera tigris tigris), female performing the Flehman response, tasting the air for mates or rivals. Endangered. Bandhavgarh, India, November.

Martin Dohrn / Stitched panoramic image of Ostracods using their light to display to mates. There are two species here, both from a new genus and neither of which has been properly described. At this stage, they are...

Martin Dohrn / Stitched panoramic image of Ostracods using their light to display to mates. There are two species here, both from a new genus and neither of which has been properly described. At this stage, they are...

Solvin Zankl / Mating behaviour in Common fruit flies (Drosophila melanogaster) studied in laboratory for gene research, a Yellow (body pigmentation) Curly (wings turn up) type mutant male mates with a Yellow, Curly...

Juergen Freund / Sacoglossan sea slug / Sap sucker (Elysia sp) a herbivore that feeds, mates and lays eggs on one type of host algae, Batangas, Philippines

Tony Heald / Black-faced Impala (Aepyceros melamis petersi) male jumping ("stotting" or "pronking") to demonstrate fitness to potential mates, competitors and predators. Devil's Thorn fl (Tribulus terrestris) in f...

Nick Upton / Two male Greenbottle flies (Eudasyphora cyanella) competing with one another as they search for mates. This is an overwintering species. Wiltshire, UK, March

Miles Barton / Filming Panamanian Golden Frog (Atelopus ziteki)reacting to the model of a waving frog. Experiment carried out to reveal the purpose of the frog's waving behaviour – to attract mates and deter rivals....

Miles Barton / Panamanian Golden Frog (Atelopus ziteki) reacting to the model of a waving frog. Experiment carried out to reveal the purpose of the frog's waving behaviour – to attract mates and deter rivals. Featur...

Solvin Zankl / Mating swarm of Long-tailed / Tisza mayfly(Palingenia longicauda) Tisza river, Hungary. Every female is approached by several mature males. Eventually the female mates with one of them on the water su...

Solvin Zankl / Mating swarm of Long-tailed / Tisza mayfly (Palingenia longicauda) Tisza river, Hungary. Every female is approached by several mature males. Eventually the female mates with one of them on the water s...

Solvin Zankl / Female Long-tailed / Tisza mayfly (Palingani a longicauda) rise up in the air soon after mating, where they form huge swarms and are out of range from males still searching for mates close to the wate...

Solvin Zankl / Female Long-tailed / Tisza mayfly (Palingani a longicauda) rise up in the air soon after mating, where they form huge swarms and are out of range from males still searching for mates close to the wate...

John Cancalosi / Wood Frog (Rana sylvatica / Lithobates sylvaticus) several males attempting to mate with a single female, males compete for mates by "scramble competition", NY, USA

John Cancalosi / Wood Frog (Rana sylvatica / Lithobates sylvaticus) several males attempting to mate with a single female, males compete for mates by "scramble competition", NY, USA

John Cancalosi / Wood Frog (Rana sylvatica / Lithobates sylvaticus) several attempting to mate with a single female, males compete for mates by "scramble competition", NY, USA

John Cancalosi / Wood Frog (Rana sylvatica / Lithobates sylvaticus) three males attempting to mate with a single female, males compete for mates by "scramble competition", NY, USA

Albert Lleal / Close up of a male moth's head and highly sensitive antennas which detect the sexual pheromones released by potential mates, Barcelona, Spain

Christian Ziegler / Misfit Leaf Frog (Agalychnis saltator) two mating in La Selva, Costa Rica, this species only mates once or twice per year, usually after a huge rain storm at the end of the dry season

Rolf Nussbaumer / Least Grebe (Tachybaptus dominicus) feeding chicks on mates back, Willacy County, Rio Grande Valley, Texas, USA. May 2004

Piotr Naskrecki / Millipede males often guard their mates by riding on their backs, Costa Rica

Piotr Naskrecki / Ghost Crab (Ocypode quadrata) fully alert male scanning the horizon for mates and rivals, Pacific coast, Costa Rica

Carol Walker / Three black bachelor stallions chasing a bay filly while blue roan stallion mates with palomino mare next to blue roan mare, bay mare, and palomino filly, Pryor Mountains, Montana, USA.

Mark Moffett / Warty Tree Toad (Hylodes asper) repeatedly kicks its leg right and left to mark its streamside territory to attract mates, Atlantic Forest, Brazil, sequence 2 of 2

Mark Moffett / Warty Tree Toad (Hylodes asper) repeatedly kicks its leg right and left to mark its streamside territory and attract mates, Atlantic Forest, Brazil, sequence 1 of 2

Norbert Wu / Adelie Penguin (Pygoscelis adeliae) group returns to rookery to relieve their mates that are brooding on nests, Cape Bird, Antarctica

Norbert Wu / One-fin Flashlight Fish (Photoblepharon palpebratum) light organ under eye used to attract mates and prey, Borneo

Norbert Wu / Sharp-nosed Frog (Ptychadena oxyrhynchus) swimming underwater, inflates body to call loudly for mates, Panama Rainforest

Michael Quinton / Common Raven (Corvus corax) male mates with a female in her nest while her partner is away, North America

Michael Quinton / Common Raven (Corvus corax) male mates with a female in her nest while her partner is away, North America

Mark Moffett / Hercules Scarab Beetle (Dynastes hercules) males fighting over female, winner of fight mates, Guadaloupe

Mark Moffett / Leafcutter Ant (Atta sexdens) queen, lives for 20 years, each colony has only one queen that mates only at the start of her life, collecting all the sperm needed to produce millions of workers, when s...

Barrie Britton / Dunnock male pecks female so she ejects sperm from previoius mating with another male; this male then mates with her. From BBC TV programme 'Life of Birds'

E.A. KUTTAPAN / Tiger female 'Sita' with large cub, Bandhavgarh National Park, India. Sita has well documented history - born Jan 1982 and has had two mates for six litters by September 1997. This juvenile male is ei...

Premaphotos / Common yellow dung fly (Scathophaga stercoraria) females being guarded by their mates as they lay eggs in dung, UK

Norbert Wu / Adelie Penguin (Pygoscelis adeliae) group return to rookery to relieve their mates that are brooding on nests, Cape Bird, Antarctica

Yves Lanceau / Domestic sheep (Ovis aries), Berrichon du Cher Sheep, ram, with marker harness for marking females that he mates with, France

Nick Upton / Common red soldier beetles (Rhagonycha fulva) nectar feeding and looking for mates on Common hogweed flowers (Heracleum sphondylium), Wiltshire, England, UK, July.

Nick Upton / Common red soldier beetles (Rhagonycha fulva) nectar feeding and looking for mates on Common hogweed flowers (Heracleum sphondylium), Wiltshire, England, UK, July.

John Cancalosi / Wood Frogs males (Lithobates sylvaticus) attempting to mate with a single female. Males compete for mates by 'scramble competition', New York, USA

Roger Powell / Greater flamingoes (Phoenicopterus roseus) meeting and selecting mates in a disused salt pan. La Tancada Salinas Nature Reserve, Ebro Delta, Catalonia, Spain