A prehistoric-looking stork as tall as an adult human and an eagle that preys on monkeys and flying lemurs are among the world's 100 most Evolutionary Distinct and Globally Endangered (Edge) birds, according to a list released by the Zoological Society of London (ZSL) and Yale University.
Edge birds represent millions of years of unique evolutionary history, said zoo management.
Carly Waterman, Edge programme manager at ZSL said: "Half of the 100 highest-ranked Edge bird species are receiving little or no conservation attention. We lament the extinction of the dodo, but without action we stand to lose one of its closest relatives, the tooth-billed pigeon or 'little dodo', and many other extraordinary birds."
See the full list of 100 birds here. In this gallery we highlight 10 of the most threatened birds (number indicates Edge rank).
1. Giant ibis (Thaumatibis gigantea). Occupying the top spot on the Edge birds list, this striking bird is the world's largest ibis. It is the national bird of Cambodia and, owing to its rarity and exceptional size, holds near-mythical status for bird-watchers, naturalists and conservationistsOMALISS KEO
4. Kakapo (Strigops habroptilus). The world's heaviest parrot, the New Zealand kakapo is also unusual in being nocturnal and flightless. The male kakapo produces a loud 'boom' call to attract potential mates which can be heard up to five kilometres away.SHANE MCINNES
8. Philippine eagle (Pithecophaga jefferyi). One of the largest and rarest eagles on the planet, this incredible predator was formerly thought to prey exclusively on monkeys. It is now known to prey on a variety of animals ranging from rodents and bats to pigs and monitor lizards.REUTERS / ALAIN PASCUA
11. Spoon-billed sandpiper (Eurynorhynchus pygmeus). This small wading bird has a unique spatula-shaped bill. Every year the birds undertake an incredible 8,000 km journey from their breeding grounds in northeast Russia to their main wintering grounds in Bangladesh and Myanmar.SMITH SUTIBUT
12. Northern bald ibis (Geronticus eremita). Once widespread across Northern Africa and Europe, this distinctive, red-faced bird has declined to just 200 breeding wild adults. There are more than 2,000 individuals in captivity, including a population at ZSL London Zoo.HEATHER BURGESS
28. Secretary bird (Sagittarius serpentarius). So-called because it supposedly resembles an old-fashioned secretary carrying quill-pens tucked behind his ears, this unmistakable African bird has an incredible method of stalking its prey, which it often stamps on before swallowing whole.REUTERS
30. Egyptian Vulture (Neophron percnopterus). This white vulture with a bright yellow bill and face is thought to be intelligent, having exhibited the use of tools to crack open large eggs. As a scavenger its diet is varied and includes carrion, tortoises, organic waste and even mammalian faeces. Despite its huge range, populations of Egyptian Vulture are declining across the globe. This is due to an array of threats like poisoning, poaching, electrocution and human disturbance.REUTERS
44. Rufous-headed Hornbill (Aceros waldeni). This colourful and distinctive bird is the world's second most endangered hornbill. Like most hornbills it possesses a bony 'casque', which protrudes from the top of its bill. Originally found on the three Philippine islands of Negros, Panay and Guimaras, it is now locally extinct from the latter due to severe deforestation.Getty
56. Juan Fernandez firecrown (Sephanoides fernandensis). This beautiful, fiery hummingbird is found on only one island off the coast of Chile. During territorial disputes, the firecrown will hover in front of the intruder and flash its crown of stunning, iridescent plumage. The male is a beautiful rich chestnut colour, while the female is blue and green. Unfortunately, we are close to losing this stunning species, which has been classified as critically endangered.PETER HODUM
73. Greater adjutant (Leptoptilos dubius). This enormous prehistoric-looking stork grows to 1.5m high with a wingspan of 2.5m. The name 'adjutant' actually refers to a military rank – it was given to this bird on account of its stiff, marching walk.REUTERS / BEN FITZGERALD