Bulldog rat

Introduced parasite wiped out native rats

Christmas Island once also had endemic rats: the bullog rat and the Maclear’s rat. Both are now extinct—most probably for the same reason. Christmas Island, which lies in the Indian Ocean and belongs to Australia, was known for its rich phosphate deposits. Therefore, in the 1890s miners founded a settlement near Flying Fish Cove to operate phosphate mining.

With the supply ship S.S. Hindustan, black rats (Rattus rattus) subsequently reached the island in 1899, introducing via fleas the pathogen Trypanosoma lewisi—a parasite that infested the rats native to Christmas Island and thus triggered an epidemic.

This is also confirmed by a study by Kelly B. Wyatt and colleagues from 2008. They examined old DNA samples of the bulldog rat and Maclear’s rat that fit into the extinction window, 1888 to 1908, as well as DNA from before the introduction of the black rats. It turned out that the bullldog and Maclear’s rats showed no signs of the pathogen before the presence of the black rats, but they did afterward.

There was also another hypothesis for the sudden disappearance of the endemic rat species on Christmas Island: hybridization, the crossing of endemic rats with introduced black rats. But Wyatt and his team were able to disprove this thesis.

Bulldog rat – fact sheet

alternative name	Christmas Island burrowing rat
scientific names	Rattus nativitatis, Mus nativitatis, Rattus navitatis, Rattus nativitatus
original range	Christmas Island (Australia)
time of extinction	1903
causes of extinction	black rats introduced to the island together with parasites
IUCN status	extinct

Extinct within eight years

Both the bulldog rat and Maclear’s rat were initially common on the island and both died out within about eight years. The bulldog rat was last documented by the vertebrate paleontologist Charles William Andrews during his ten-month stay on Christmas Island between 1897 and 1898, during which he collected six specimens.

In the book A Monograph of Christmas Island (Indian Ocean), Andrews stated in 1900 that he had already noticed a decline in the rodent species at that time. And when Andrews finally visited the island again in 1908, he declared the bulldog rat extinct.

Oldfield Thomas writes in On the Mammals of Christmas Island (1888) that in 1887 two further specimens of the bulldog rat were collected by the British zoologist Joseph Jackson Lister.

Already during a visit to Christmas Island in 1904, according to an article by J. Pickering and C. A. Norris published in 1996 in the journal Australian Mammalogy, no native rats could be collected any longer. At this point, the bulldog rat must therefore already have been extinct.

In addition, Andrews wrote in 1909 in On the Fauna of Christmas Island about the company doctor Dr. McDougal, who between 1902 and 1904 had seen “native rat species crawling about in their death throes during the day.” Whether this description can also be related to the bulldog rat or exclusively to Maclear’s rat remains unclear so far.

Little is known about the bulldog rat

Little is known about the habits and behavior of the bulldog rat. It can be assumed that it owed its English name Bulldog Rat to its compact body with the short tail. The animal, which reached up to 42 centimeters in length, also had a hard layer of fat around two centimeters thick on its back, which indeed recalls the bulky shape of a bulldog.

Because of the powerful tail, the large claws, and the strong paws, experts assume that the rodent could dig well. The species was also frequently observed in and around caves, and unlike Maclear’s rat it could not climb trees.

During the day the animals stayed hidden under roots, in hollow trees, or in rotting plant matter, and they were active at night. Bulldog rats preferred dense forests and higher regions of the island.