Historical records for the Bcga district wcix' examined to chart the environmental changes wixiught by Europeans thivugh habitat alteration and the introduction of exotic species, and to intcrpi-ct the anpact of these on native manimals. Early recorded increases in native mammal populations, particularly koalas, niay have been attrihutahle to a decline in Aboriginal hunting pressure. .After settlement in IS30. the valley forest was cleared pivgi'cssively, ecosystems were altered by grazing and impi-oved pastures, and many introduced plants became weeds in the disturbed enviivnment. The timber industry exploited the foi'ests of the valley and then the slopes of the sunvunding mountains. Three exotic manunal species had a major impact on the district -hai'cs. I'abbits and foxes. Ofthe native fauna, the large and medium sized mammal species were those recoided most frequently. Dramatic fluctuations in numbers occurred in most of these species, and many reached plague proportions between 1880 and 1910, after which their numbers fell sharply. The peaks of exotic mammals and the decline of native mammals coincided with the clearing of the i-emaimngforests in the Bega \ 'alley. Many native mammal species are now rare, four aiv in danger of extinction, and at least six species have become locally extinct since settlement. As most ofthe native mammal populations in the district now occur in the State Forests suri-ounding the Bega I'alley, the importance of presei'ving or managing these foi'ests for wildlife must be weighed against proposals to manage the forests for pulpwood (woodchip) production.

The aim of this study was to describe the roosts of Nyctophilus bifax in littoral rainforest in Iluka Nature Reserve on the north coast of New South Wales. Radio-telemetry was used to track 17 bats in November 1988 (lactation season) and 11 in May 1989 (mating season) to 87 roosts in 49 trees within the littoral rainforest. The bats frequently changed roosts, which were clustered within a small area. During November, lactating females moved twins between diurnal roosts and some carried twins while foraging. Twins represented a load of up to 95% of their mother's bodyweight. Bats roosted communally in foliage and tree hollows, beneath peeling bark, among epiphytes, and between strangler figs and host trees. Hollows were used more frequently when bats were lactating, while the use of foliage roosts was greater during the mating season. Roosts were concentrated in four tree species, although a wide range of other tree species was used. Roost trees used in November were taller (17 m) than those used in May (8.2 m), and refiect selection oi Syzygium leuhmannii and Acmena hemilampra, both trees of the forest interior. The converse applied for selection of Cupaniopsis anacardioides, a small tree of the littoral zone, in May. These results identify the need for conserving a diversity of roosts for this species of bat.

The murine rodent genus Microhydromys Tate and Archbold, 1941, includes the smallest of the native rodents of New Guinea and is the rarest Australo-Papuan rodent genus preserved in world museums. We discuss the morphological characteristics of Microhydromys and diagnose two species in the genus: M. richardsoni Tate and Archbold, 1941, distributed over northern New Guinea, and M. argenteus, n. sp., recorded from three localities in southern New Guinea. The only other species previously classified in the genus-Microhydromys musseri Flannery, 1989-is reallocated to the genus Pseudohydromys Rü mmler, 1934. The little available information relating to their biology indicates the species of Microhydromys to be terrestrial inhabitants of foothill and lower montane forest formations and probably naturally rare in those environments.