The study was initially a long term study of the ecology of small mammals at Mlawula Nature Reserve in the eastern part of Swaziland. Due to the drought and dwindling numbers of rodents in the reserve the study was redirected to determining the factors resulting in the low numbers. The impacts of food and cover and grazing by the larger ungulates were studied. In addition, the age class distribution and gastro-intestinal parasites of small mammals were studied. A study of the small mammals in the Siphiso Valley of Mlawula Nature Reserve was conducted over four years from August 2000. The population density, biomass and composition of the small mammal community in the area were studied. The community comprised of Mus minutoides A. Smith, 1834, Mastomys natalensis (A. Smith, 1834), Lemniscomys rosalia (Thomas, 1904), Crocidura hirta Peters, 1952, Steatomys pratensis Peters, 1846 and Graphiurus murinus (Desmarest, 1822). Mus minutoides was the dominant species with pregnant females caught from November to May. Species richness varied significantly with the time of the year. The biomass, density and numbers of small mammals were low and by the end of the second year of the study, small mammal density was close to zero. Mastomys natalensis from a Middleveld study site, Luyengo, Swaziland were used to study the age structure of the population by means of eye lenses. The eye lens to age (in days) curve determined by Leirs (1994) was applied. A large percentage of M. natalensis in winter (June) were 2 months old while in spring/summer (October to March) the population consisted mainly of 3 month old specimens. A very low number of specimens were older than 4 months. This suggests a high mortality/removal rate of the young especially in the winter months. The impact of grazing pressure and rainfall on small mammal densities were investigated. High grazing pressure by ungulates rendered the habitat unsuitable for small mammals as it removed cover and encouraged colonization by alien invasive plant species. This effect was exacerbated by diminishing and unpredictable rains, such that mild grazing pressure negatively impacted on small mammal communities and on individual species. When the small mammals disappeared from the study site, M. natalensis was reintroduced to determine the factors that led to the disappearance. Supplementary food resulted in the longest persistence of the reintroduced mice while the impact of additional cover was small. Predation was likely responsible for the rapid decline of the reintroduced mice. Small mammals were examined for ectoparasites and gut parasites as these were thought to negatively impact on their physiology and reproduction. Ectoparasites collected included the ticks Ixodes sp. and Boophilus sp., the mite Allodermanyssus sp. and another species of mite. The gastrointestinal tracts contained the helminths Syphacia sp., Heligmonina sp., Trichuris sp., Protospirura sp., two unidentified nematode species and different cestode species. A new species of heligmosomoid nematode is described and named. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.