Rod Williams / African pygmy goose (Nettapus auritus) male in foreground and female behind, Captive, occurs Madagascar

Alex Mustard / The smaller male ornate Ghost Pipefish (Solenostomus paradoxus) turns belly to belly with the larger female ghost pipefish and fertilises the eggs in her brood pouch. Unlike many seahorses, pipefish a...

Peter Cairns / 2020VISION / Gannet (Morus bassanus) mutual preening, Bass Rock, Firth of Forth, Scotland, UK, June

Peter Cairns / 2020VISION / Gannet (Morus bassanus) pair preening each other, Bass Rock, Firth of Forth, Scotland, UK, June

Frederique Olivier / Blue eyed shag / cormorant (Phalacrocorax atriceps) pair resting at nest with chick, Macquarie Island, Southern Atlantic, Australian Antarctica, December

Fergus Gill / Northern gannet (Morus bassanus) pair having a dispute with the bird on the neighbouring nest. Troup Head, Scotland, August.

John Cancalosi / American toad (Bufo americanus) or "Hop toad" pair in amplexus, the male (top) clasping the female. New York, USA, Jan 2000

Juan Carlos Munoz / Pair of Rockhopper penguins (Eudyptes chrysocome) with egg, with a group of penguins in the background. Penguin Island, Puerto Deseado, Patagonia, Argentina, Nov 2008

Gary K. Smith / Chalkhill blue butterflies (Polyommatus coridon) male and female in courtship behaviour, Norfolk, UK, August

Charlie Summers / King Cormorants (Phalacrocorax atriceps) courting atop their nesting site, strengthening the pair bond. Sea Lion Island, Falkland Islands

Charlie Summers / Pair of King Cormorants (Phalacrocorax albiventer) courtship ritual, on the coastline, Sea Lion Island, Falkland Islands, November

Charlie Summers / Pair of Rockhopper Penguins (Eudyptes chrysocome) copulating, Saunders Island, Falkland Islands, December

Charlie Summers / Pair of Rockhopper Penguins (Eudyptes chrysocome) preening in courtship display, Saunders Island in the Falkland Islands, November

Doug Wechsler / Male and female American toads (Bufo americanus) in amplexus on road at night, with car headlights behind. Philadelphia, Pennsylvania, USA

Doug Wechsler / Male and female American toads (Bufo americanus) in amplexus on road at night, with car headlights behind. Philadelphia, Pennsylvania, USA. March

Doug Wechsler / Girl watching male and female American toads (Bufo americanus) in amplexus crossing road at night; Philadelphia, Pennsylvania, USA. March

Suzi Eszterhas / Pair of Blanchard's Cricket Frogs (Acris crepitans blanchardi) Red Corral Ranch, Texas, USA

Russell Cooper / A pair of mating Blue-tailed damselflies (Ischnura elegans) Morden, South London. UK, July

Fabio Liverani / Alpine Newts (Triturus alpestris) male and female displaying courtship behaviour, Captive. From Traversari lake, Campigna National Park, Emilia Romagna and Tuscany regions, Italy

Fabio Liverani / Alpine Newts (Triturus alpestris) male and female displaying courtship behaviour, Captive. From Traversari lake, Campigna National Park, Emilia Romagna and Tuscany regions, Italy

Fabio Liverani / Alpine Newts (Triturus alpestris) male and female displaying courtship behaviour, Captive. From Traversari lake, Campigna National Park, Emilia Romagna and Tuscany regions, Italy

Fabio Liverani / Crested Newts (Triturus cristatus carnifex) male and female in courtship display, Captive. Found in Traversari lake, Campigna National Park, Emilia Romagna and Tuscany regions, Italy

Fabio Liverani / Smooth Newt (Triturus vulgaris) courtship between male and female. (Captive) Found in Traversari lake, Campigna National Park, Emilia Romagna and Tuscany regions, Italy

Fabio Liverani / Smooth Newt (Triturus vulgaris) courtship between male and female. (Captive) Found in Traversari lake, Campigna National Park, Emilia Romagna and Tuscany regions, Italy

Fabio Liverani / Smooth Newt (Triturus vulgaris) courtship between male and female. (Captive) Found in Traversari lake, Campigna National Park, Emilia Romagna and Tuscany regions, Italy

Fabio Liverani / Smooth Newt (Triturus vulgaris) courtship between male and female. (Captive) Found in Traversari lake, Campigna National Park, Emilia Romagna and Tuscany regions, Italy

Fabio Liverani / Pair of Alpine Newts (Triturus alpestris) male and female displaying courtship behaviour, Traversari lake, Campigna National Park, Emilia Romagna and Tuscany regions, Italy

Tom Vezo / Willet {Tringa semipalmatus} male displaying to female, Texas, USA

LYNN M. STONE / Pair of Trumpeter Swans (Cygnus buccinator) in courtship display, wintering on Mississippi River, Minnesota, USA

LYNN M. STONE / Pair of Trumpeter Swans (Cygnus buccinator) in courtship display, wintering on Mississippi River, Minnesota, USA

Paul Harcourt Davies / Nine potted moths (Amata phegea) mating pair. Montecucco, Tuscany, Italy, Europe.

Nick Garbutt / A pair of Short-horned Chameleons (Calumma brevicornis) mating. Rainforest understorey, Andasibe-Mantadia National Park, Madagascar.

Hanne & Jens Eriksen / Arabian toad {Bufo arabicus} mating pair, Oman, March

Hanne & Jens Eriksen / Arabian toad {Bufo arabicus} mating pair, Oman, March

Eric Baccega / Pair of Northern gannets (Morus bassanus) displaying, Bonaventure island Quebec Canada

Eric Baccega / Pair of Northern gannets (Morus bassanus) displaying, Bonaventure island Quebec, Canada

Luiz Claudio Marigo / Pair of King / Thoas Swallowtail butterflies (Papilio thoas) mating, Pantanal of Mato Grosso, Mato Grosso State, Center-west of Brazil.

LYNN M. STONE / Trumpeter Swans (Cygnus buccinator) and Mallard duck, wintering on Mississippi River, Minnesota, USA

LYNN M. STONE / Trumpeter Swans (Cygnus buccinator) "gabbing" during courtship behaviour on Mississippi River, Minnesota, USA, February

LYNN M. STONE / Trumpeter Swans (Cygnus buccinator) two adults and two juveniles, in flight over Mississippi River, Minnesota, USA

LYNN M. STONE / Trumpeter Swans (Cygnus buccinator) showing courtship behaviour on Mississippi River, Minnesota, USA

Dietmar Nill / Northern gannet (Morus bassanus) bringing nest material to nest, Helgoland, Germany

David Kjaer / Adonis blue butterfly (Polyommatus bellargus) pair mating, on flower, Dorset, England, May

Roy Mangersnes / Antarctic Shag (Leucocarbo bransfieldensis) pair preening on Useful Island, Antarctica. November.

David Woodfall / Little terns (Sternula albifrons) pair changing over incubation at nest, Northumberland, UK

David Woodfall / Little tern (Sternula albifrons) pair at nest scrape with Sandeel prey for newly hatched young, Northumberland, UK

David Woodfall / Little tern (Sternula albifrons) bringing Sandeel prey to nest, with sitting bird and newly hatched young, Northumberland, UK

David Woodfall / Little tern (Sternula albifrons) feeding newly hatched chicks with Sandeel, Northumberland, UK

David Woodfall / Little tern (Sternula albifrons) pair creating nest scrape, Northumberland, UK

David Woodfall / Little tern (Sternula albifrons) pair, one taking off, the other feeding in marked scrape nest on raised fish boxes to prevent flooding by rising sea levels, Northumberland, UK

David Woodfall / Little tern (Sternula albifrons) pair, one on nest the other taking off, Northumberland, UK

David Woodfall / Little tern (Sternula albifrons) pair, one on nest, Northumberland, UK

David Woodfall / Little tern (Sternula albifrons) pair displaying aggression towards Arctic tern (Sterna paradisaea) above, Northumberland, UK

David Woodfall / Little tern (Sternula albifrons) pair, one in flight, the other feeding, in marked nest on raised fish box to prevent flooding by rising sea levels, Northumberland, UK

David Woodfall / Little tern (Sternula albifrons) courtship prior to nest scrape creation, Northumberland, UK

Wild Wonders of Europe / Hermansen / Two Northern gannets (Morus bassanus) interacting, Saltee Islands, County Wexford, Republic of Ireland, June 2009

Wild Wonders of Europe / Hermansen / Gannet (Morus bassanus) courtship, Saltee Islands, County Wexford, Republic of Ireland, June 2009

Angelo Gandolfi / Two Moroccan Spiny-tailed Lizards (Uromastyx acanthinurus), male (right, green) and female (left), Morocco.

Claudio Contreras / Royal tern (Thalasseus maximus) pair greeting each other, Rasa Island Special Biosphere Reserve, Sea of Cortez (Gulf of California) Mexico, April

Claudio Contreras / Royal tern (Thalasseus maximus) pair, post-mating dance, Rasa Island Special Biosphere Reserve, Sea of Cortez (Gulf of California) Mexico, April

Wild Wonders of Europe / Green / Northern gannets (Morus bassanus) displaying, Saltee Islands, Republic of Ireland, May 2008

Stephen Dalton / Cave spider (Meta menardi) pair with egg-sac, UK

Adrian Davies / Drinker Moth {Euthrix potatoria} male and female pair, Devon, UK, August.

Nick Upton / Male Banded demoiselle damselfly (Calopteryx splendens) flying down to mate with a female perched on a riverside leaf after hovering above her, Wiltshire, UK, summer

Nick Upton / Male Banded demoiselle damselfly (Calopteryx splendens) gripping female with tail claspers before flying off in tandem and mating, Wiltshire, UK, May

Nick Upton / Male Banded demoiselle damselfly (Calopteryx splendens) hovers near a female perched on a riverside leaf, Wiltshire, UK, summer

Nick Upton / Male banded demoiselle damselfly (Calopteryx splendens) flying down to mate with a female perched on a riverside leaf after hovering above her, Wiltshire, UK, summer

Nick Upton / Banded demoiselle damselflies (Calopteryx splendens) fanning wings as they mate in the wheel position, Wiltshire, UK, May

Nick Upton / Male Banded demoiselle damselfly (Calopteryx splendens) gripping female with tail claspers as she prepares to mate in wheel position, Wiltshire, UK, May

Rod Williams / Silver Gull (Chroicocephalus novaehollandiae) pair on rock on ground, Burleigh Heads, SE Queensland, Australia, March

John Cancalosi / American toad (Bufo americanus) pair in amplexus, laying eggs, New York, USA

John Cancalosi / American toad (Bufo americanus) pair in amplexus, laying eggs, New York, USA

John Cancalosi / American toad (Bufo americanus) pair in amplexus, New York, USA

John Cancalosi / American toad (Bufo americanus) pair in amplexus laying eggs, New York, USA

John Cancalosi / American toad (Bufo americanus) pair in amplexus laying eggs, New York, USA

Wild Wonders of Europe / Allofs / Greater flamingo (Phoenicopterus roseus) pair mating, in lagoon, Pont Du Gau, Camargue, France, April 2009

Hanne & Jens Eriksen / Arabian toads {Bufo orientalis arabicus} mating pair, showing size difference of the male and female, Wakan, Oman

Ross Couper-Johnston / Great egret {Ardea alba} nesting colony, Ibera Marshes, Argentina

Jose B. Ruiz / Booted eagle (Aquila pennata) pair with chick at nest in Pine woods, Murcia, Spain

John Waters / Mute swan (Cygnus olor) courtship, swimming close together and copying each other's actions, Somerset, UK, Spring 2009

John Cancalosi / American Toad (Bufo americanus) pair in amplexus, mating, female laying eggs, NY, USA

John Cancalosi / Wood Frog (Rana sylvatica / Lithobates sylvaticus) pair in amplexus, mating, NY, USA

Gabriel Rojo / Rockhopper penguin (Eudyptes chrysocome / crestatus) pair, social preening, Penguin Island, Ria de Puerto Deseado Nature Reserve, Santa Cruz Province, Patagonia, Argentina, December

John Cancalosi / Wood Frog (Rana sylvatica / Lithobates sylvaticus) pair in amplexus, mating, NY, USA

Gabriel Rojo / Crested duck (Lophonetta specularioides) pair, Ria de Puerto Deseado Nature Reserve, Santa Cruz Province, Patagonia, Argentina, December

Edwin Giesbers / Northern gannets (Morus bassanus) pair, Heligoland, Germany

Edwin Giesbers / Northern gannets (Morus bassanus) mating, Heligoland, Germany

Edwin Giesbers / Northern gannet (Morus bassanus) pair courtship, Heligoland, Germany

Tim Laman / Pied Herons (Egretta picata) pair at the water's edge, Karawari River vicinity, East Sepik Province, Papua New Guinea

Steve Knell / Northern gannets (Morus bassanus) displaying at breeding colony, Saltee Islands, County Wexford, Republic of Ireland, May

Steve Knell / Northern gannets (Morus bassanus) displaying in colony, Saltee Islands, County Wexford, Republic of Ireland, May

Steve Knell / Northern gannets (Morus bassanus) displaying in symetry at breeding colony, Saltee Islands, County Wexford, Republic of Ireland, May