Rats!

One of the commonest rodents in Malta, and the islands surrounding it, is the black rat Rattus rattus (L., 1758). It is usually found living together with man in highly artificial habitats all around the world, but has spread to any area where the temperature is warm enough and where food is in plentiful supply. Since this species is an omnivore (eats both vegetable and animal material), it also creates problematic issues when introduced in areas of ecological uniqueness.

In Malta this problem is seen in mostly relation to the unique reptilian fauna - on the islands of Selmunett, predatory actions of Rattus sp. are the main factors involved in the virtual extinction of the lizard Podarcis filfolensis kieselbachi (Fejervary, 1924), while the introduction of rats on General's Rock may result in the same situation with the lizard Podarcis filfolensis generalensis (Gulia, 1914) (cf. Sciberras & Schembri, 2008; Borg & Sultana, 2003).

The following black rat skulls have been found in Holocene deposits in Buskett and Mistra respectively. The other rat found in the Maltese Islands is the brown rat Rattus norvegicus (Berkenhout, 1769) which, despite its common name, can look highly similar to the black rat in form and colouration.

Examination of the skull, however, makes identification easier.

Black rat Rattus rattus (L., 1798) - specimens from Buskett (left) and Mistra (right). Top photo shows dorsal aspect of the skull, while the bottom photo shows the ventral aspect.

The black rat skull (as can be seen above) has a markedly pointed posterior end, whereas the brown rat's is more rounded. This feature is seen marked with a '1' in the drawings below. In addition, the bony ridges above the eyes also display a distinct difference. They are curved in the skull of the black rat while almost straight in the brown rat's. This feature is seen marked with a '2' in the drawings below. Both drawings are taken from the very interesting paper by Yiğit et al. (1998).

Black rat Rattus rattus (L. 1758) skull drawing

Brown rat Rattus norvegicus (Berkenhout, 1769) skull drawing

References:

Borg, J. J. & Sultana, J., 2003. The presence of the black rat Rattus rattus on Fungus Rock (Maltese islands). The Central Mediterranean Naturalist, 4 (1): 105-106.

Sciberras, A. & Schembri, P. J., 2008. Conservation status of St Paul's Island Wall Lizard (Podarcis filfolensis kieselbachi). Herpetological Bullettin, 105: 28-34.

Yiğit, N., Çolak, E., Sözen, M. & Özkurt, Ş., 1998. The taxonomy and karyology of Rattus norvegicus (Berkenhout, 1769) and Rattus rattus (Linnaeus, 1758) (Rodentia: Muridae) in Turkey. Turkish Journal of Zoology, 22: 203-212.