Fauna
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While no mammals exist on North Keeling, land crabs are conspicuous on the forest floor, seabirds are prolific with many species breeding, and there is a host of small invertebrates present.
Vertebrates
The only terrestrial vertebrates recorded from North Keeling Island are birds, the Gecko (Lepidodactylus lugubris) and the rabbits (Oryctolagus cuniculus). The Gecko is relatively uncommon (Stokes and Cogger 1987) while the rabbit was an early introduction that had disappeared by the 1880s (Guppy 1890).
Reptiles
Lepidodactylus lugubris has successfully colonised many oceanic islands, a success partly attributed to its ability to reproduce asexually. Nesting Green turtles occur occasionally on the southern atoll, but frequently on North Keeling. Although Hawksbill turtles are seen around the island, nesting has not been recorded. The only species of sea snake recorded from the southern atoll is the Yellow-bellied sea-snake (Pelamis platurus).
Birds
When Charles Darwin visited the Cocos (Keeling) Islands in April 1836, the "immense number" of marine birds recorded in 1828-29 on the main atoll (cited Gibson-Hill 1949) were probably still present though somewhat diminished. The reason for the decline in birds of the main atoll was almost certainly due to habitat change, intense hunting by people and predation by cats and rats.
Today there are very few birds on the main atoll. Birds remain in large numbers on North Keeling Island due to its isolation, the difficulty of landing, the absence of any feral animals and access restrictions placed by the former Clunies Ross family up to the mid 1970s . Of the approximately sixty species of birds recorded from the Cocos (Keeling) Islands, twenty-five have been seen on North Keeling Island in recent times. Fourteen of the latter are seabirds, eleven of which breed on the Island.
Fourteen species recorded from North Keeling Island are listed for protection under the Japan-Australia and China-Australia Migratory Birds Agreements (JAMBA & CAMBA). The island is the focus of seabirds over a huge expanse of the central-eastern Indian Ocean, is one of the few remaining pristine tropical islands in the Indian Ocean and is of unique importance to the ocean's seabird biota.
The status of many seabird species on the island is precarious and careful management is required if they are not to follow the decline in seabird populations evident on other Indian Ocean islands over the past 100 years.
By far the most numerous seabird on North Keeling Island is the Red-footed Booby (Sula sula). Based on comprehensive population surveys between 1985 and 1996, the current population is estimated at 22,000 breeding pairs, making it one of the most important colonies of Red-footed Boobies in the world. However, the population is by no means stable. Of 16 known breeding populations of Red-footed Boobies in the Indian Ocean, only four, including North Keeling Island, remain. North Keeling Island has in fact the largest colony of Red-footed Boobies in either the Australian region or the Indian Ocean. Large numbers of birds of all ages have been harvested by Cocos-Malays over the last century and this has undoubtedly had a significant effect on the population status.
Least and Great Frigate birds (Fregata ariel and F. minor), also occur on the island in large numbers with possibly 3,000 breeding pairs of Least Frigate birds with a smaller number of Great Frigate birds. This is the second largest population of Least Frigate birds in Australia and in the Indian Ocean. Numbers of these two species have also been depleted by harvesting.
The Cocos Buff-banded Rail (Rallus phillipensis andrewsi) is significant as the only endemic bird in the island group. It is a common bird on North Keeling Island and occurs in all habitats. It frequently forages along the lagoon shore, apparently eating crustacea which are abundant in the seagrass deposited along the tide line. The Rail is now probably extinct on the southern atoll, due largely to habitat destruction. The population on North Keeling Island is between 500 - 800 individuals, and the species is listed as endangered.
White-tailed Tropicbirds (Phaethon lepturus) are a common sight in the skies above North Keeling Island spiralling upwards in the thermal eddies. They nest in moderate numbers in hollows of mature Pisonia and Cordia trees. Several species of migratory waders are occasionally seen feeding on the lagoon shoreline.
The Herald Petrel, listed as a critically endangered species, has not been found in Pulu Keeling National Park since it was first discovered in the mid-eighties.
Invertebrates
Crabs are the most conspicuous and probably the most numerous inhabitants of the forest floor and beach fringe. The Little Nipper (Geograpsus grayi) is common under the Pisonia forest. The robber crab (Birgus latro) listed in the IUCN Red Data Book (1981) as being vulnerable to extinction, is occasionally observed within the forest but was more abundant prior to harvesting by Cocos-Malays.
Three species of hermit crabs are present in large numbers - the Red hermit crab (Coenobita perlata) the Purple hermit crab (C. brevimana) and the Tawny hermit crab (C. rugosa). The Land crab (Cardisoma carnifex) is abundant, particularly in the saltmarsh and on the fringes of the lagoon. Yellow Nippers (Geograpsus crinipes) and the Red crab (Gecarcoidea natalis) also occur. The Horn-eyed Ghost crab (Ocypode ceratophthalma) is commonly found on the north-western beaches with Grapsus (Grapsus tenuicrustatis) common on rock sections of the coast.
A species of cricket Ornebius sp., occurs among the leaves of both Cordia and Pisonia, and Nerius lineolatus, a long-legged Dipteran, and the mosquito (Aedes aegypti) are plentiful. Butterflies, ants, cockroaches, beetles and weevils are also represented. Spiders, a small wood-louse, various species of ectoparasitic ticks and mites, scorpions, termites, a centipede and a terrestrial mollusc (Melampus sp.) have been recorded but as yet no millipedes or earthworms have been found.