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

Frederique Olivier / Close-up of a pair of Black browed albatrosses (Thalassarche melanophris) mutual grooming, New Island, Falkland Islands.

Bence Mate / Hyacinth macaws (Anodorhynchus hyacinthinus) mutual preening, Estrada Parque, Pantanal, Brazil.

Denis-Huot / Grant's zebra (Equus burchelli granti) mutual grooming after a bush fire, Masai-Mara Game Reserve, Kenya. October.

Terry Whittaker / 2020VISION / Konik horse (Equus caballus) mutual grooming, wild herd in rewilding project, Wicken Fen, Cambridgeshire, UK, June 2011

Carol Walker / Mustangs / wild horses, two cremello colts Claro and Cremosso interacting, mutual grooming, McCullough Peaks herd, Wyoming, USA, August 2007

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

Peter Cairns / 2020VISION / Pair of Gannets (Morus bassanus) mutual preening, Bass Rock, Firth of Forth, Scotland, UK, June. Photographer quote: 'I never get tired of watching gannets. This pair who momentarily lined up in perfe...

Wild Wonders of Europe / Hamblin / Two Konik horse foals mutual grooming, Oostvaardersplassen, Netherlands, June 2009 WWE BOOK

Wild Wonders of Europe / Radisics / Przewalski horses (Equus ferus przewalskii) mutual grooming, Hortobagy National Park, Hungary, May 2009

Roger Powell / Rainbow Lorikeets (Trichoglossus haematodus) courtship preening. Victoria, Australia

Roger Powell / Rainbow Lorikeets (Trichoglossus haematodus) courtship preening. Victoria, Australia

Anup Shah / Common zebra mutual grooming (Equus quagga), Serengeti NP, Tanzania

Mark Moffett / Ant (Pseudomyrmex sp) group drink nectar from Whistling Thorn (Acacia drepanolobium) acacia tree and protect the tree from leaf eating enemies ensuring mutual survival, Costa Rica

Karl Ammann / Bonobo family mutual grooming, Wamba, Zaire

Anup Shah / Lion females mutual grooming Masai Mara Kenya

Anup Shah / Common zebra {Equus burchelli} mutual grooming. Masai Mara, Kenya

Anup Shah / Chimpanzees mutual grooming {Pan troglodytes schweinfurtheii} Gombe NP, Tanzania. 2002

Anup Shah / Chimpanzees mutual grooming {Pan troglodytes schweinfurtheii} Gombe NP, Tanzania. 2002

Mike Read / Black-browed albatross (Thalassarche melanophrys) pair at nest mutual preening, Saunders Island, Falkland Islands, November.

Ernie Janes / Black-faced impala (Aepyceros melampus) mutual grooming, Namibia.

Richard Du Toit / Two Burchell's zebra (Equus quagga burchellii) mutual grooming with a Cattle egret (Bubulcus ibis) perched on back of one, Rietvlei Nature Reserve, South Africa.

Mike Read / Black-browed albatross (Thalassarche melanophrys) pair at nest mutual preening, Saunders Island Falkland Islands, November.

Frederique Olivier / Pair of Black browed albatrosses (Thalassarche melanophris) mutual grooming, with two Southern rockhopper penguins (Eudyptes chrysocome) in the background, New Island, Falkland Islands.

Frederique Olivier / Pair of Black browed albatrosses (Thalassarche melanophris) mutual grooming, New Island, Falkland Islands.

John Cancalosi / Pair of Northern gannets (Morus bassanus) mutual gooming, Canada, August.

John Cancalosi / Pair of Northern gannets (Morus bassanus) mutual gooming, Canada, August.

John Cancalosi / Pair of Northern gannets (Morus bassanus) mutual gooming, Canada, August.

Frederique Olivier / Two Olive baboons (Papio anubis) mutual grooming, Lake Manyara NP, Tanzania.

Tui De Roy / Snares Crested penguin (Eudyptes robustus) pair courtship mutual preening. Snares Island, New Zealand Sub-Antarctic Islands. Endemic and vulnerable species.

John & Mary-Lou Aitchison / Female European otter (Lutra lutra) and cub mutual grooming, Scotland, UK, November.

SCOTLAND: The Big Picture / Moorhen (Gallinula chloropus) pair courtship, mutual preening, St John's Pool Bird Reserve, Thurso, Caithness, Scotland, UK, May.

Konrad Wothe / Chimpanzees (Pan troglodytes) mutual grooming, Mahale Mountains National Park, Tanzania.

Konrad Wothe / Chimpanzee (Pan troglodytes) sitting with a baby and grooming itself, panning to a pair mutual grooming, Mahale Mountains National Park, Tanzania, East Africa.

Konrad Wothe / Chimpanzees (Pan troglodytes) mutual grooming, with a baby wandering around, Mahale Mountains National Park, Tanzania, East Africa.

Mike Potts / Southern royal albatross (Diomedea epomophora) mutual preening behaviour at the nest, Campbell Island, Subantarctic New Zealand January

Jussi Murtosaari / Common ravens (Corvus corax) mutual preening, Northern Ostrobothnia, Finland, MArch.

Andy Trowbridge / Two Yellow eyed penguins (Megadyptes antipodes) mutual preening. Katiki Point, Moeraki, Otago, New Zealand. January. Endangered species.

Carol Walker / Two bay Wild Mustang horses mutual grooming, McCullough Peaks Herd Area, Wyoming, USA.

Mark Hamblin / Northern Gannet (Morus bassanus), pair mutual preening. Bass Rock (East Lothian), Scotland, July

Kristel Richard / Two Lipizzaner foals mutual grooming, Piber Federal Stud, Maria Lankowitz, Koflach, Styria, Austria, September. Editorial use only.

Will Watson / Welsh Ponies (Equus caballus) engaged in mutual grooming, Llanbedr Hill, Powys, Wales, August.

Mark MacEwen / Wedge-tailed Shearwaters (Puffinus pacificus) outside nest burrow mutual grooming at night, Heron Island, southern Great Barrier Reef, Queensland, Australia. Taken with infra-red camera.

Suzi Eszterhas / Chimpanzee (Pan troglodytes) groups mutual grooming in tropical forest, Western Uganda

LYNN M. STONE / Guernsey cows mutual grooming in autumn pasture, East Granby, Connecticut, USA. (Non-ex)

Christophe Courteau / Aerial view of Gelada Baboons mutual grooming (Theropithecus gelada) Simien NP, Ethiopia, 3000m altitude

Christophe Courteau / Gelada Baboon (Theropithecus gelada) mutual grooming, Simien NP, Ethiopia, 3000m altitude

Christophe Courteau / Gelada Baboon (Theropithecus gelada) family mutual grooming, Simien NP, Ethiopia, 3000m altitude

Tui De Roy / Swallow-tailed gull (Creagrus furcatus) pair mutual preening in courtship. Genovesa Island, Galapagos Islands, Ecuador, June.

LYNN M. STONE / Black Vultures (Coragyps atratus) in courtship behaviour- (mutual grooming and head-touching. Sarasota County, Florida, USA, April.

Sue Daly / Hermit crab (Pagurus prideaux) with cloak Anemone (Adamsia carcinopados) Channel Islands, UK October

Brent Stephenson / Female Chacma Baboon (Papio ursinus) with male behind grooming her. Kruger National Park, South Africa, January.

Carol Walker / Wild horses / Mustangs, two mutual grooming, McCullough Peaks, Wyoming, USA

Carol Walker / Wild horses / Mustangs, two pintos, mutual grooming, McCullough Peaks, Wyoming, USA

Carol Walker / Wild horses / Mustangs, two foals mutual grooming, McCullough Peaks, Wyoming, USA

Carol Walker / Wild horses / Mustangs, pinto mare and foal mutual grooming, McCullough Peaks, Wyoming, USA

Florian Möllers / Quinling Golden snub nosed monkey (Rhinopitecus roxellana qinlingensis), adult male and female hugging each other in a tree. Zhouzhi Nature Reserve, Qinling Mountains, Shaanxi, China.

Brent Stephenson / Pair of Australasian gannets (Morus serrator) mutual preening at the nest. Cape Kidnappers, Hawkes Bay, New Zealand, September.

Ben Osborne / A young male African lion (Panthera leo) grooms a lioness, Savuti, Botswana. Taken on location for BBC Planet Earth series 2005

Ben Osborne / A young African lioness (Panthera leo) grooms a young male lion, Savuti, Botswana. Taken on location for BBC Planet Earth series 2005

Ben Osborne / A young African lioness (Panthera leo) grooms a young male lion, Savuti, Botswana. Taken on location for BBC Planet Earth series 2005

Ben Osborne / A young male African lion (Panthera leo) grooms a lioness, Savuti, Botswana. Taken on location for BBC Planet Earth series 2005

Ole Jorgen Liodden / Nazca Booby (Sula granti) pair mutual grooming. Galapagos

Brent Stephenson / Two Shetland Ponies (Equus caballus) mutual grooming, Shetland, Scotland, UK, August.

Anup Shah / White faced whistling ducks (Dendrocygna viduata) preening each other, Masai Mara National Reserve, Kenya

Kristel Richard / Konik horses (Equus caballus) - wild Konik breeding stallion mutual grooming with one of his wild Konik mares, Arnhem natural reserve, Netherlands, April

Fiona Rogers / Bonobo (Pan paniscus) two males grooming, Lola Ya Bonobo Sanctuary, Democratic Republic of Congo. October.

Carol Walker / Wild Horses / mustangs, two foals mutual grooming, Pryor Mountains, Montana, USA, June

Carol Walker / Mustangs / wild horses, two cremello colts interacting, mutual grooming, two years, McCullough Peaks herd, Wyoming, USA, August 2009

Carol Walker / Wild Horses / mustangs, two foals mutual grooming, Pryor Mountains, Montana, USA, June

Carol Walker / Mustangs / wild horses, two cremello colts Claro and Cremosso interacting, mutual grooming, McCullough Peaks herd, Wyoming, USA, August 2007

Carol Walker / Wild Horses / mustangs, two mares mutual grooming, McCullough Peaks Herd Area, northern Wyoming, USA, August

Carol Walker / Wild Horses / mustangs, two pintos mutual grooming, McCullough Peaks Herd Area, northern Wyoming, USA, June

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 / Royal Penguin (Eudyptes schlegeli) mutual preening, Macquarie Island, Southern Atlantic, Australian Antarctica, November

Suzi Eszterhas / Macaroni penguin (Eudyptes chrysolophus) mutual preening, Cooper Bay, South Georgia, January

LYNN M. STONE / Guernsey Cow (on left) mutual grooming with Red and White Holstein, Connecticut, USA

LYNN M. STONE / Guernsey Cow (Left) licking neck of Red and White Holstein, mutual grooming, Connecticut, USA, October

Christophe Courteau / Unusual grooming behaviour between a Common / Crested caracara (Caracara plancus) and a Black vulture (Coragyps atratus) Pantanal, Brazil, July

Tui De Roy / Swallow-tailed Gull (Creagrus furcatus) pair mutual preening in courtship, Galapagos Islands, Ecuador

Jean E. Roche / White horses of the Camargue mutual grooming on wetlands, Camargue, France, January 2009

Andrew Walmsley / Two Yellow eyed penguins (Megadyptes antipodes) mutual preening, Otago Peninsula, New Zealand, February

Tom Marshall / Yellow eyed penguin (Megadyptes antipodes) pair engaged in mutual preening, Otago Peninsula, New Zealand, February, Endangered species

Andy Rouse / Two Burchell's zebras (Equus quagga) mutual resting allows tail to protect face from flies, Masai Mara, Kenya

Andy Rouse / Common / Burchell's zebra (Equus quagga) mutual fly protection in the heat, Masai Mara, Kenya

Carol Walker / Mustang / Wild Horse foal and yearling, mutual grooming at sunset, McCullough Peaks Herd Area, Cody, Wyoming, USA,

Carol Walker / Wild horses / Mustangs, mare and yearling mutual grooming, Pryor Mountains, Montana, USA

Carol Walker / Two young colts mutual grooming, Mustangs, McCullough Peaks Herd Area, Cody, Wyoming, USA

Pete Oxford / Nazca booby (Sula dactylatra granti) pair, mutual preening, Punta Cevallos, Española / Hood Island, Galapagos Islands

Pete Oxford / Nazca boobies (Sula dactylatra granti) pair, mutual preening, Punta Cevallos, Española / Hood Island, Galapagos Islands

Steven David Miller / Sulphur-crested cockatoo {Cacatua galerita galerita} pair mutual grooming, Grampians National Park, Victoria, Australia

Steven David Miller / Sulphur-crested cockatoo {Cacatua galerita galerita} pair mutual grooming, Grampians National Park, Victoria, Australia