Rediscovery of rodents (GenusNesoryzomys) considered extinct in the Galápagos Islands

Abstract

The history of the endemic rodents of the Galapagos Islands began with the discovery of the first Galapagos rice rat species by Charles Darwin in 1835 and the last species was described as recently as 1980. Unfortunately, of the seven described species known to occur in the islands during the past 150 years, only two were known to be extant to 1995. Since then, two expeditions to the Galapagos Islands have been conducted to survey endemic rodent populations. The first confirmed the existence of a small endemic rice rat, Nesoryzomys fernandinae, on Fernandina, known previously only from owl pellet remains found in 1979. In 1997, an expedition to Santiago revealed a population of the larger rice rat N. swarthi, a species collected alive only once in 1906 and considered extinct in all recent literature on the Galapagos Islands. Survey efforts on Santa Cruz resulted only in the collection of introduced rodent species (Rattus rattus, R. norvegicus and Mus musculus). The extant species of native rodents in the Galapagos Islands now number four: N. narboroughi and N. fernandinae on Fernandina; N. swarthi on Santiago; and Oryzomys bauri on Santa Fe. Three species are found on islands where no introduced rodents or cats occur, whereas only one (N. swarthi) co-exists with R. rattus and M. musculus. Nesoryzomys darwini and N. indefessus on Santa Cruz and O. galapagoensis on San Cristobal are still considered extinct. Strategies for conservation should include monitoring islands for introduced rodents and cats, development of emergency plans in the event of introductions, and captive management .

Diversity, distribution, and conservation of endemic island rodents

“…In the future, without successful conservation initiatives, many other threatened species of rodents that are currently ''continental'' in distribution could follow this Australian path to become insular ''pseudo-endemics'' on small coastal islands. Rodent pseudo-endemism also applies to the Galapagos, where Nesoryzomys indefessus and Oryzomys galapagoensis were formerly distributed across multiple islands but today survive only on the islands of Fernandina and Santa Fe, respectively (Dowler et al, 2000;Musser and Carleton, 2005).…”

“…However, reliance on flagship taxa is not always an effective path to conservation of less charismatic species in the same areas. Conservationists should remember the cases of rodents like Hypogeomys on Madagascar and Nesoryzomys on Galapagos, which are declining even while some targeted flagship species are flourishing or stable in these areas (Dowler et al, 2000;Sommer and Hommen, 2000). Further, on smaller and more remote islands, large mammals and birds may be absent.…”

Understanding Invasive Species in the Galapagos Islands

“…Of the seven species that existed, there are only four extant species. One was discovered in Fernandina (Nesoryzomys fernandinae), and the other (Nesoryzomys swarthi) was discovered in 1997, on Santiago (Dowler et al 2000). This rat is the only one of four remaining Galapagos rats of the original 12 species that lived in the same island as the introduced rat (Harris and Macdonald 2007).…”

Sydney's bubonic plague outbreak 1900-1910: a disaster for foreshore wildlife?

“…Extinction was suspected to result from direct competition and disease that was spread by Black Rats. Surprisingly, in 1997, the largest of the previously listed extinct native rats, the Santiago Rat N. swarthi, was rediscovered living sympatrically with Black Rats on Santiago Island (Dowler et al 2000). There was no evidence of strong spatial segregation, differences in home range size or temporal activity between the two species, but there was an increase in activity of the Santiago Rat pre-dawn and post-dusk in areas of high Black Rat density (Harris et al 2006).…”