There are about 9,993 living species of birds known by scientists. A collaboration between scientists at Yale and the Zoological Society of London (ZSL) have analyzed all of them and determined the world’s avian biodiversity. This is part of ZSL’s Evolutionary Distinct and Globally Endangered (EDGE) species list, and they have ranked 100 bird species based on conservation status and how unusual they are compared to other birds.

The list includes representatives from 20 of the 29 known orders. The birds are declining in population for a variety of reasons, though poaching, habitat destruction, and introduced predators are the most common threats.

The top 15 are listed here with details and pictures, and the rest of the list follows below:

1. Giant Ibis (Thaumatibis Gigantea)

Image credit: Henrick Grönvold

The Giant Ibis is critically endangered, with only about 230 mating pairs left in the wild. Most surviving members live in Cambodia, though there are a few living in Laos and Vietnam. This is the largest of the ibises, measuring up to 100 cm (39 in) tall and weighing up to 4.2 kg (9.3 lbs).

2. New Caledonian Owlet-nightjar (Aegotheles savesi)

Image credit: Joseph Smidt

The conservation status of this bird, which is endemic to New Caledonia, isn’t well known. It is believed that there are probably less than 50 individuals remaining, but scientists haven’t seen any of this species since 1998, which is the only sighting since 1960.

3. California Condor (Gymnogyps californianus)

Image credit: Stacy via WikiMedia Commons

In 1987, there were so few California Condors that all 21 remaining individuals were collected and the species was declared extinct in the wild. Through dedicated breeding programs, the birds were reintroduced into protected areas in 1991. There are now over 237 living in the wild. These huge birds have a 3 m (9.8 ft) wingspan and weigh up to 12 kg (26 lbs)

4. Kakapo (Strigops habroptila)

Image credit: Mnolf via WikiMedia Commons

This nocturnal flightless bird, endemic to New Zealand, is critically endangered with only 130 wild individuals remaining. The kakapo is the heaviest species of parrot, weighing up to 4 kg (9 lbs) when it reaches adulthood.

5. Kagu (Rhynochetos jubatus)

Image credit: Scott Meyer

The Kagu is endemic to New Caledonia and has a structure that is only found in members of this species: nasal corns. This is a structure which covers the nostrils, which is believed to shield dirt from entering the nostrils when the bird digs for insects.

6. Bengal Florican (Houbaropsis bengalensis)

Image credit: Richard Leydekker

There are likely fewer than 500 adults remaining of this species, which live in isolated populations in India and Southeast Asia. This species is the most threatened of all bustards, which are large terrestrial birds. Bengal Floricans grow up to 68 cm (27 in) in height and weigh up to 1.9 kg (4.2 lbs).

7. Forest Owlet (Heteroglaux blewitti)

Image credit: Dr. Raju Kasambe

This owl is endemic to India and was first believed to be extinct in 1884. A small population was discovered in 1997 and only 25 birds have been located since 2000, though it is estimated that there could be as many as 250 individuals remaining.

8. Philippine Eagle (Pithecophaga jefferyi)

Image credit: Harry Balais

This eagle is endemic to the Philippines and grows to an incredible 102 cm (3.4 ft) tall and can weigh up to 8 kg (17.6 lbs). Its crest of feathers resembles the mythical griffin, which is part lion, part eagle. Estimates on the number of breeding pairs varies, and could be as few as 82 or as many as 233 (which really isn’t that many).

9. Christmas Island Frigatebird (Fregata andrewsi)

Image credit: Shah Jahan

This bird is endemic to the Christmas Island, Australia. Its top predator is the yellow crazy ant, which was inadvertently introduced via trade ships. The ants attack the birds during breeding season.

10. Sumatran Ground-cuckoo (Carpococcyx viridis)

This bird is endemic to Sumatra and can grow up to 55 cm (22 in) in length. There are estimated to be fewer than 250 individuals left. Over a 90 year period, the bird has only been spotted twice; most recently from a tiger camera trap in 2006, though its call was identified in 2007.

11. Spoon-billed Sandpiper

12. Northern Bald Ibis

13. Plains-wanderer

14. New Zealand Storm-petrel

15. Hooded Grebe

16. White-shouldered Ibis

17. Maleo

18. Black-hooded Coucal

19. Madagascar Serpent-eagle

20. Dwarf Olive Ibis

21. Rufous Scrub-bird

22. Noisy Scrub-bird

23. Junin Grebe

24. White-collared Kite

25. Congo Bay-owl

26. White-eyed River-martin

27. Red-headed Vulture

28. Secretarybird

29. Peruvian Diving-petrel

30. Egyptian Vulture

31. St Helena Plover

32. Australian Painted Snipe

33. Cuban Kite

34. Tooth-billed Pigeon

35. Nahan's Francolin

36. Sulu Hornbill

37. Shoebill

38. Purple-winged Ground-dove

39. Asian Crested Ibis

40. Sangihe Shrike-thrush

41. Jerdon's Courser

42. Lesser Florican

43. Kokako

44. Rufous-headed Hornbill

45. Masked Finfoot

46. Bahia Tapaculo

47. Waved Albatross

48. Stresemann's Bristlefront

49. Sociable Lapwing

50. Eskimo Curlew

51. Slender-billed Curlew

52. Bannerman's Turaco

53. Ashy Storm-petrel

54. Siberian Crane

55. White-throated Storm-petrel

56. Juan Fernandez Firecrown

57. Dark-winged Trumpeter

58. Uluguru Bush-shrike

59. Polynesian Ground-dove

60. Sichuan Jay

61. Mountain Serpent-eagle

62. Sulu Bleeding-heart

63. Zapata Rail

64. Mindoro Bleeding-heart

65. Kaka

66. Negros Bleeding-heart

67. Black Stilt

68. Makira Moorhen

69. Great Indian Bustard

70. Abbott's Booby

71. Kittlitz's Murrelet

72. Titicaca Grebe

73. Greater Adjutant

74. Western Bristlebird

75. Eastern Bristlebird

76. Shore Plover

77. Udzungwa Forest-partridge

78. Madagascar Fish-eagle

79. White-bellied Heron

80. Subdesert Mesite

81. Long-whiskered Owlet

82. Philippine Cockatoo

83. Spix's Macaw

84. South Island Wren

85. Crow Honeyeater

86. Northern Brown Kiwi

87. Banded Ground-cuckoo

88. Flores Hawk-eagle

89. Tachira Antpitta

90. Beck's Petrel

91. Cebu Flowerpecker

92. Blue-eyed Ground-dove

93. Javan Trogon

94. Pulitzer's Longbill

95. Alagoas Antwren

96. Pernambuco Pygmy-owl

97. Jamaica Petrel

98. Grenada Dove

99. Wood Snipe

100. Rio de Janeiro Antwren