In conjunction with studies of the rodent populations of the former nuclear test site at Eniwetok Atoll, the feeding patterns of Rattus rattus and Rattus exulans were detennined by food acceptance tests, histological examination of stomach contents, and observation of animals under both natural and cage conditions. Both species were active in all community types from the early successional stages to the shrub-tree stage. R. exulans was found mainly on islets having the remnants of coconut plantations, whereas R. rattus occurred on those extensively disturbed by nuclear testing. Plant foods predominated in the diets of both species; however, R. rattus used a wider range of foods, including a variety of insects. The apparent narrower preferences of R. exulans might explain its absence from islets that suffered habitat destruction and restriction of food sources during the nuclear test program.In the summers of 1964 to 1968, studies of rat populations were conducted at Eniwetok Atoll. This paper reports the feeding patterns of the roof rat (Rattus rattus) and Polynesian rat (Rattus exulans) based on analyses of stomach contents of trapped specimens and the relative acceptability of various atoll plants to live rats. Observation of rats in cages and under natural conditions afforded additional information on their feeding behavior.Eniwetok Atoll (Fig. 1) is a ring of 40 low coral islets located approximately at latitude 11°30' N, longitude 162°15' E, in the northern Marshall Islands. The land surface of the atoll occupies about 2.25 square miles (Woodbury, 1962). Islet size ranges from narrow bars, less than 1 acre, to about 300 acres for the larger islets, such as Engebi and Eniwetok. Annual rainfall is about 55 inches; but because of the poor holding capacity of the surface, most of the fresh water is lost through percolation and evaporation. Mean temperature at the atoll is 82°F, with little seasonal fluctuation; relative humidity averages near 80 per cent.The atoll has been extensively disturbed-first by many years of human occupancy, then by the events of World War II, and most recently by the United States nuclear testing program during the years 1948 to 1958. In the course of nuclear testing, some islets were denuded of vegetation. Soil and organic material were evaporated in large areas around test centers and waves, generated by tests in the lagoon, washed and scoured parts of the atoll surface.The atoll's most mature vegetation (on Igurin, for example) occurs as mixed forest among the old coconut plantations. Primary elements in these forests are Cacas nucifera, Pisonia grandis, Cardia subcardata, Terminalia samoensis, OchrasUz appositifalia, Guettarda speciasa, and M arinda citrifalia. The extensively disturbed islets (for example, Engebi and Runit, Fig. 2) were revegetated first by grasses (Lepturus repens ), sedges (Fimbristylis atallensis ), and creeping morning glory (Ipamaea sp.). Later, shrub and tree vegetation, primarily 69
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