Conservation status

In April 2003 the IUCN Red List of Threatened Species listed 54 sigmodontine species. Three sigmodontines, Neso-ryzomys darwini, N. indefessus, and Oryzomys nelsoni, are considered to be extinct; four other species, Nectomys parvipes, Oryzomys gorgasi, Rhagomys rufescens, and Sigmodontomys aphrastus, are listed as Critically Endangered. Ten sigmodontines species are considered Endangered, 13 Vulnerable, one species Near Threatened, and 19 to be at Lower Risk. Data are deficient to evaluate the status of four species. For the sole fact that the understanding of species limits of most sigmodontine genera is far from being settled, these figures are subject to change. For instance, instead of subsuming Oryzomys galapagoensis under O. bauri, Dowler et al. (2000) recognize both forms as distinct Galápagos endemic species. This classificatory scheme implies that another sigmodontine species, O. galapagoensis that has not been collected since 1835, should be regarded as extinct.

One of the major sigmodontine threats is habitat destruction due to land conversion for urbanization and agricultural and logging expansion. Another important threat is the introduction of exotic fauna. For instance, the most likely cause of the extinction of the Galápagos endemic Nesoryzomys dar-wini and N. indefessus is the introduction of black rats (Rattus rattus), either through the introduction of pathogens to which native species were susceptible, or through direct competition. Similarly, Megaroyzomys, another Galápagos endemic, became extinct presumably in historic times, through predation by introduced dogs, cats, pigs, and Rattus. Hunting pressure may be considered as a minor threat affecting sigmodontine conservation. Mann (1945) suggested that in some Chilean areas extensive trapping may have seriously reduced the populations of Chinchillula.

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