Monday 25 January 2021

Pallas’s Squirrel in Hong Kong: Feral pets, an introduced or reintroduced species…or even a range expansion?

Fifty years ago the sight of a wild squirrel in Hong Kong would have been unthinkable. But now, Pallas’s Squirrel (Callosciurus erythraeus) can be seen both on Hong Kong Island and in the New Territories. I have no reason to doubt the story that these populations were from the accidental or intentional release of squirrels imported for the pet trade. Well…perhaps a nagging doubt.

Pallas's Squirrel photographed in the New Territories of
Hong Kong by AJP, December 2020. Note the black
'spot' near the end of the tail. In the second photograph
the red belly can be glimpsed.

In the 1960s these squirrels, along with Siberian Chipmunks, were being sold as pets in Hong Kong. The ‘lab boys’ had a couple in a tiny cage in their room in the Zoology Department of the University of Hong Kong, for example. In view of the appearance of flocks of feral Yellow-crested Cockatoos we perhaps should not have been too surprised to have seen squirrels in the trees of Government House on our first return to Hong Kong in 1997.

The standard account of these squirrels in Hong Kong is that the ones on Hong Kong Island are different from those in the New Territories. Those on the island are described as belonging to the subspecies C.e. thai, with those in the New Territories as C.e. styani, the former from Thailand; the latter from Northern China. I am not sure how the feral animals in Hong Kong were assigned to these subspecies and having looked up some of the original papers I am even less sure about the identification of thai other than Thailand is perhaps where the animal dealers said they were imported from. The black hairs near the tip of the tail of the ones from the New Territories do, however, fit the description of styani. The import of the Siberian Chipmunk, Eutamias sibiricus, is also compatible with the importation of C.e. styani, into Hong Kong from the same area of northern China.

In many parts of its range the belly of the squirrel, as its specific name implies, is some shade of red. That is true of those in the New Territories of Hong Kong. That was not the case in at least some of those kept as pets. The ones the lab boys kept were a light yellowish grey—as were those we saw in the gardens of Government House 30 years later.

It does seem odd that a native squirrel had never been reported for Hong Kong. The question is if they were once there and had been extirpated or had never even been part of the native fauna. Two squirrels apparently from near Canton (now Guangzhou)—only 135 km (85 miles) from Hong Kong—were collected by John Reeves between 1812 and 1831; the skins are in the Natural History Museum in London. They are currently assigned to a subspecies, C.e. castaneoventris, with a distribution south of the Pearl River including the island of Hainan. Nothing seems to be known in formal descriptive terms of the Pallas’s Squirrels that occur over much of China (including the mainland north of the Pearl River adjacent to Hong Kong) and this leads me to the first of my nagging questions: is it just possible that the squirrels in the New Territories of Hong Kong are not feral but are native squirrels that have come over the border as Hong Kong became reforested after the devastation of the hillsides for firewood during and shortly after the Japanese occupation?

The whole taxonomy of squirrels of the genus Callosciurus seems to this outsider as a mess, in part due simply to a lack of series of specimens from most parts of the range. Clarity has not be advanced by simplistic molecular phylogenetic studies (using only mitochondrial DNA). That leaves me with a second nagging question: why, if two apparent subspecies were imported for the pet trade in the 1960s has one become feral in mainland Hong Kong and the other on Hong Kong Island? Surely, both would have been sold in the pet shops and bird markets on both sides of the harbour. Did they interbreed on the mainline side and if so does that mean that the ‘styani’ coloration is dominant to the ‘thai’?

Tackling the questions on the origins of the Pallas’s Squirrels would also help settle the obvious corollary: can those in Hong Kong be classified as an ‘introduction’ or a ‘re-introduction’ or even a natural range expansion?

Lurz PWW, Hayssen V, Geissler K, Bertolino S. 2013. Callosciurus erythraeus (Rodentia: Sciuridae). Mammalian Species 45, 60-74.

Moore JC, Tate GHH. 1965. A study of the diurnal squirrels, Sciurinae, of the Indian and Indochinese subregions. Fieldiana 48. Chicago: Chicago Natural History Museum.

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