Biraj Sarkar/ BIA / Ashy-headed Green Pigeon (Treron phayrei) feeding on fruit, Darjeeling, India

Graeme Guy / Pink-necked Green-Pigeon (Treron vernans) male feeding on berries, Kedah, Malaysia

Loic Poidevin / African Green Pigeon (Treron calvus) on a branch, Masai Mara, Kenya. March.

Loic Poidevin / African Green Pigeon (Treron calvus) on a branch, Masai Mara, Kenya. March.

Loic Poidevin / African Green Pigeons (Treron calvus) interacting in a tree, Masai Mara, Kenya. March.

Staffan Widstrand / Wild Wonders of China / Common emerald dove (Chalcophaps indica) Tongbiguan nature reserve, Dehong, Yunnan, China

Staffan Widstrand / Wild Wonders of China / Common emerald dove, (Chalcophaps indica) Tongbiguan nature reserve, Dehong, Yunnan, China

Staffan Widstrand / Wild Wonders of China / Common emerald dove (Chalcophaps indica) Tongbiguan nature reserve, Dehong, Yunnan, China

Staffan Widstrand / Wild Wonders of China / Asian emerald dove (Chalcophaps indica) walking over a branch in Hong Bung He, Dehong, Yunnan, China.

Debapratim Saha/ BIA / Pin-tailed Green-Pigeon (Treron apicauda), West Bengal, India

Eric Sohn Joo Tan/ BIA / Green Imperial-Pigeon (Ducula aenea), Udawalawe National Park, Sri Lanka

Ann & Steve Toon / Emerald-spotted dove wood (Turtur chalcospilos), Zimanga Private Game Reserve, South Africa.

Oriol Alamany / Emerald dove (Chalcophaps indica) on grounf in coastal forest, Lord Howe island, Lord Howe Island Group UNESCO Natural World Heritage Site, New South Wales, Australia, October.

Charlie Summers / Emerald-spotted wood dove (Turtur chalcospilos) on branch, Ruaha National Park, Tanzania.

Ole Jorgen Liodden / Emerald-spotted wood dove (Turtur chalcospilos) Zimanga, South Africa

Roger Powell / Grey-capped Emerald Dove (Chalcophaps indica) at rest in a park. Mary River, Northern Territory, Australia

Cyril Ruoso / African green pigeon (Treron calva) flock flying, Lake Lobak / Lobeke National Park, South East Cameroon, July.

Rod Williams / Male Black naped fruit dove (Ptilinopus melanospila) perched on branch, captive, occurs in South East Asia.

Aflo / White-bellied green pigeons (Treron sieboldii) perched in tree, Takyama, Gifu, Japan.

Ann & Steve Toon / Emerald-spotted wood dove (Turtur chalcospilos), Zimanga private Game Reserve, KwaZulu-Natal, South Africa

Dong Lei / Thick-billed green pigeon (Treron curvirostra) group of three drinking from puddle, Xishuangbanna National Nature Reserve, Yunnan Province, China. March.

Dong Lei / Pin-tailed green pigeon (Treron curvirostra) and Thick-billed green pigeon (Treron curvirostra) group foraging in mud. Xishuangbanna National Nature Reserve, Yunnan Province, China. March.

Steve O. Taylor (GHF) / Pink necked green pigeon (Treron vernans) for sale in cages, Singkawang, West Kalimantan, Indonesian Borneo. July 2010.

Hanne & Jens Eriksen / Common emerald dove (Chalcophaps indica) Thailand, February.

Pete Oxford / Congo green pigeon (Treron calvus calvus) flock in flight, Lango Bai, Republic of Congo (Congo-Brazzaville), Africa.

Debapratim Saha / Pin-tailed Green-Pigeon (Treron apicauda) pair taking flight, Darjeeling, India

Ashish & Shanthi Chandola / Orange-breasted green pigeon (Treron bicinctus), Yala National Park, Sri Lanka.

Dong Lei / Emerald Dove (Chalcophaps indica) on ground, Xishuangbanna National Nature Reserve, Yunnan Province, China, Asia

Dong Lei / Wedge-tailed Green Pigeon (Treron sphenura) Zhangmu County, Qinghai-Tibet Plateau, Tibet, China, Asia

Michael D. Kern / Nicobar pigeon (Caloenas nicobarica) feather against black background.

Loic Poidevin / Emeraud-Spotted Wood Dove (Turtur chalcospilos) foraging on ground, Bogoria Lake, Kenya.

Ralph Martin / Bruce's Green-Pigeon (Treron waalia), Oman

Ralph Martin / African Green-Pigeon (Treron calvus) flock flying, Okavango Delta, Botswana

Jabruson / Nesting Green Pigeon (Treron calvus) in riverine forest along the Rutshuru river. Rwindi sector of the Virunga National Park, Democratic Republic of Congo.

Jabruson / Flock of Green Pigeons (Treron calvus) taking off after feeding, Rutshuru river. Rwindi sector of the Virunga National Park, Democratic Republic of Congo.

Roland Seitre / Emerald dove (Chalcophaps indica) Lifou, Loyalty Islands, New Caledonia.

Roland Seitre / Emerald dove (Chalcophaps indica) Lifou, Loyalty Islands, New Caledonia.

Roland Seitre / Emerald dove (Chalcophaps indica) Lifou, Loyalty Islands, New Caledonia.

Laurent Geslin / Yellow legged green pigeon {Treron phoenicoptera} Sariska NP, India

Pete Oxford / African Green-Pigeon (Treron calvus) flock flying, Lango Bai, Odzala-Kokoua National Park, Democratic Republic of the Congo

Cyril Ruoso / African Green-Pigeon (Treron calvus) flock flying, Cameroon

Martin Willis / African Green-Pigeon (Treron calvus) sunning itself on a branch, Lake Mburo National Park, Uganda

Loic Poidevin / Yellow legged green pigeon (Treron phoenicoptera) Keoladeo Ghana National Park, Bharatpur, Rajasthan, India, March

Tim Fitzharris / Pink-necked Green-Pigeon (Treron vernans) pair, Jurong Bird Park, Singapore

Tom Vezo / Mourning Dove (Zenaida macroura), Green Valley, Arizona

Sebastian Kennerknecht / Bruce's Green-Pigeon (Treron waalia), Hawf Protected Area, Yemen

Steve Nicholls / Close up of feathers of Nicobar pigeon (Caloenas nicobarica) from south east asia

Tui De Roy / African Green-Pigeon (Treron calvus), Solio Game Reserve, Kenya

Christophe Courteau / Speckled / Green pigeon (Columba guinea) and moon, South Africa, June

Patricio Robles Gil / Two African green pigeon {Treron calva} feeding in bush, Kruger NP, South Africa

Patricio Robles Gil / African green pigeon {Treron calva} perched in bush, Kruger NP, South Africa

David Tipling / Pompadour green pigeon (Treron pompadora) perched at the top of a tree, Subic, Luzon, Philippines

Tim Laman / Thick-billed green-pigeon (Treron curvirostra) female in fig tree, Subterranean River National Park, Palawan Island, Philippines. October

Tim Laman / Thick-billed green-pigeon (Treron curvirostra) male in fig tree, Subterranean River National Park, Palawan Island, Philippines. October

Hanne & Jens Eriksen / Bruce's green pigeon {Treron waalia} perched in tree, Ayn Razat, Dhofar, Oman

Hanne & Jens Eriksen / Bruce's green pigeon {Treron waalia} perched in tree, Ayn Razat, Dhofar, Oman

Tom Vezo / White-winged Dove (Zenaida asiatica) on cactus, Green Valley, Arizona

Tom Vezo / White-winged Dove (Zenaida asiatica) on cactus, Green Valley, Arizona

Tom Vezo / White-winged Dove (Zenaida asiatica) wading in puddle, Green Valley, Arizona

Tom Vezo / Mourning Dove (Zenaida macroura) portrait, Green Valley, Arizona

Bernard Castelein / Yellow legged green pigeon (Treron phoenicoptera) feeding on berries. Ranthambore NP, Rajasthan, India

Tom Vezo / White-winged Dove (Zenaida asiatica) perching, Green Valley, Arizona

Tom Vezo / White-winged Dove (Zenaida asiatica) perching in tree, Green Valley, Arizona

Tom Vezo / White-winged Dove (Zenaida asiatica), Green Valley, Arizona

Pete Oxford / African green pigeon (Treron calva) in bush. Okavango Delta, Botswana, Southern Africa

Peter Waechtershaeuser/ BIA / Orange-breasted Green-Pigeon (Treron bicincta), Sri Lanka

Graeme Guy/ BIA / Thick-billed Green-Pigeon (Treron curvirostra) male, Penang, Malaysia

Roland Seitre / Makatea Grey-Green Fruit-Dove (Ptilinopus chalcurus) at nest, Tuamotus archipelago, French Polynesia. Endemic and vulnerable species.

Pete Oxford / African Green-Pigeon (Treron calvus) flying near mineral lick, Lango Bai, Odzala-Kokoua National Park, Democratic Republic of the Congo

Pete Oxford / African Green-Pigeon (Treron calvus) flock flying near mineral lick, Lango Bai, Odzala-Kokoua National Park, Democratic Republic of the Congo

Tim Fitzharris / Pink-necked Green-Pigeon (Treron vernans) pair, Jurong Bird Park, Singapore

Tom Vezo / White-winged Dove (Zenaida asiatica) bathing, Green Valley, Arizona

Suzi Eszterhas / African Green-Pigeon (Treron calvus), Okavango Delta, Botswana

Julian Hume / Illustration of extinct pigeons. Clockwise from top right: red-moustached fruit dove (Ptilinopus mercieri tristrami) - extinct 1920,Hivoa,Maquesas; Marquesas fruit dove (Ptilinopus mercieri mercieri)...

Mike Read / African green pigeon {Treron calva} perched in tree, Kruger National Park, South Africa

Thoswan Devakul / Thick billed green pigeon female (Treron curvirostra) Thailand, Pang Sida NP

Bruce Thomson / Emerald dove (Chalcophaps indica) male, perched on branch, Wet Tropics World Heritage, Lake Eacham, Queensland, Australia.

Bruce Thomson / Emerald dove (Chalcophaps indica) male, perched on branch, Wet Tropics World Heritage, Lake Eacham, Queensland, Australia

Tom Vierus / Many-colored fruit-dove (Ptilinopus perousii) female, perched in tree, Turtle Island, Yasawa Islands, Fiji.

Brian Bevan / European turtle dove (Streptopelia turtur) perching in Hawthorn (Crataegus sp.) bush and calling, Bedfordshire, UK, June.

Roland Seitre / Island imperial pigeon (Ducula pistrinaria) perched on branch, stretching its wings, Hong-Kong Gardens, Hong Kong. Captive, occurs in New Guinea.

Roland Seitre / Island imperial pigeon (Ducula pistrinaria) perched on branch, Hong-Kong Gardens, Hong Kong. Captive, occurs in New Guinea.

Roland Seitre / Red-knobbed imperial-pigeon (Ducula rubricera) portrait, Solomon Islands. Captive.

Roland Seitre / Two Red-knobbed imperial-pigeons (Ducula rubricera) portrait, Solomon Islands. Captive.

Roland Seitre / Two Red-knobbed imperial-pigeons (Ducula rubricera) perched in the rain, one flapping its wings, Solomon Islands. Captive.

Roland Seitre / Two Blue-tailed imperial pigeons (Ducula concinna) perched on branch, New Guinea. Captive.

Roland Seitre / Blue-tailed imperial pigeon (Ducula concinna) perched on branch, New Guinea. Captive.

Roland Seitre / Two Indian green imperial-pigeons (Ducula aenea sylvatica) perched on branch, China. Captive.

Roland Seitre / Green imperial-pigeon (Ducula aenea aenea) perched on branch, Sulawesi, Indonesia. Captive.

Roland Seitre / Two Green imperial-pigeons (Ducula aenea aenea) perched on branch, Sulawesi, Indonesia. Captive.

Roland Seitre / Two Green imperial-pigeons (Ducula aenea aenea) perched on branch, Sulawesi, Indonesia. Captive.

Roland Seitre / Green and white zone-tailed pigeon (Ducula forsteni) perched on branch, Sulawesi, Indonesia. Captive.

Roland Seitre / Green and white zone-tailed pigeon (Ducula forsteni) perched on branch, Sulawesi, Indonesia. Captive.

Roland Seitre / Atoll fruit-dove (Ptilinopus coralensis) perched on branch, Rangiroa,Tuamotus, French Polynesia.

Roland Seitre / Black-naped fruit dove (Ptilinopus melanospilus) male, perched in tree feeding on fruit, Borneo.

Roland Seitre / Black-naped fruit dove (Ptilinopus melanospilus) male, perched in tree feeding on fruit, Borneo.