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