By Eileen Westwig, Collections Manager in the Museum’s Life Collections.
About 320 km south of Java in the Indian Ocean lies Christmas Island. Although discovered and named on Christmas Day in 1643, the island remained unexplored until its first settlement in 1888, a development which had dire consequences for some of its native species.
Christmas Island is home to a variety of endemic animals such as rats, land crabs, butterflies and many birds. The accumulation of bird droppings over thousands of years made the island rich in phosphate, and the commercial potential of these deposits brought many expeditions to the island. With the ships’ cargo came black rats.
Two species of endemic rats, Maclear’s Rat (Rattus macleari) and the Bulldog Rat (Rattus nativitatis) went extinct within 20 years of settlement, despite having been previously very numerous on the island.
Maclear’s Rat, seen at the top of the page in an illustration from an 1887 publication, was described as chestnut brown above, with a partly white, long tail. It was once the most numerous mammal on the island ‘occurring in swarms’. The Bulldog Rat had a much shorter tail and a layer of subcutaneous fat up to 2 centimetres thick, the function of which is unknown to this day.
The likely cause of their extinction was the introduction of diseases by the ship rats, to which the Christmas Island rodents had no immunity. The disappearance of the native rats also had a knock-on effect: the parasitic Christmas Island Flea (Xenopsylla nesiotes) depended on the rats as hosts, and so the fleas became extinct with the rats’ demise.
In 1901 Dr. Herbert E. Durham, a British parasitologist investigating the origins of beriberi disease, led an expedition to Christmas Island. During his visit he collected several specimens of Maclear’s Rat, but was unable to find any Bulldog Rats, despite a lengthy search and the offer of a reward. Two of the nine Maclear’s Rats Durham obtained showed abundant parasites, trypanosomes, in their blood.
Christmas Island possesses quite a number of peculiar species in its fauna, and it is regrettable that observations were not made before animals had been imported to this isolated station, as well as that my own notes are so incomplete.
Dr. Herbert E. Durham
Durham also found blood parasites in the native fruit bats (Pteropus melanotus) but noted that these were unlikely to have been introduced, instead were “an old standing native occurrence.” These bats still inhabit various islands in the Indian Ocean, including Christmas Island, where they are critically endangered.
The Museum holds a range of material from Christmas Island, including six skins and three skulls of Rattus macleari, which were collected by H. E. Durham in 1901-02, and donated in 1938.
Visit the Museum’s Presenting… case between now and 6 March to see Christmas Island specimens from the collections.