The Heath Mouse Pseudomys shortridgei was discovered in South Australia when a museum specimen collected from Kangaroo Island in 1967 was re-identified in 2000 and during trapping in the lower South East since 2001. These and subfossil records are summarized and compared with information from Western Australia and Victoria. Preliminary morphological comparisons of the single recent Kangaroo Island specimen and those from mainland South Australia and Victoria showed some differences in fur colour and body size. A total of 20 subfossil deposits containing P. shortridgei were documented in southern South Australia, spanning the Victorian to Western Australian borders. It and M. musculus were recorded together at only two sites, both surface deposits where material of different ages could have been mixed. At excavated sites, layers in which P. shortridgei was found were dated at <700 yBP in the lower South East of South Australia but the species was absent from layers dated <2000 yBP on the coast of the Nullarbor Plain. Pseudomys shortridgei was found in undated surface deposits collected from the Eyre and Yorke Peninsula along with other rodents that are both extinct and extant in the surrounding habitats. At these deposits, relative abundance compared with other rodents varied from 2.7 to 8.5%. Trapping of extant populations in the lower South East of South Australia has yielded trap successes of 2.0–13.3%, a range that is broadly comparable with other states. Intensive surveys in the last 20 years have not trapped P. shortridgei on Kangaroo Island and its status there is unknown. Long-term climatic cycles (increasing aridity), and habitat clearance and fragmentation have probably resulted in the decline of P. shortridgei in South Australia.
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