Survival of Rats at Eniwetok AtollI WILLIAM B. JACKSON2

THE STORY of rats at Eniwetok Atoll (Marshall While proof is lacking, I believe that the only Islands) and their apparently uncanny ability to rodent at Eniwetok Atoll prior to the initiation survive atomic detonations and inhabit areas of the AEC program in 1946 was the Polynesian with high levels of radiation has been referred rat (Rattus exulans). This is the common rat of to in various documents (Berrill, 1966; Hines, the Pacific islands, having moved with the 1962 and 1966; French, 1965; Woodbury, Micronesians from island to island. Probably 1962); all are to some degree incomplete or in only the larger islets of the atoll (those with error. The purpose of this paper is to pull to­ coconut plantings) were infested. gether the fragments of data that are available Although the Germans, and later the Japa­ and, at this late date, attempt to piece together nese, were active in the Marshall Islands in the the story of the survival of rat populations at first half of the twentieth century, no specific Eniwetok. records of rodents for Eniwetok Atoll seem to exist. St. John (1960) indicated that no botan­ HISTORICAL BACKGROUND ical accounts existed from German (or the Eniwetok and Bikini atolls in the northern earlier Spanish) explorations. While botanical Marshall Islands were involved in the United collections were made by the Japanese, I can States nuclear testing program between 1946 find no descriptions of rats, and no rodent and 1958. During this period six major opera­ specimens from Eniwetok Atoll were present whe~ exa~ined tions were carried out at Eniwetok Atoll and I the collection in the Japanese involved some 40 detonations. Many devices Natwnal SCience Museum in Tokyo. No speci­ were small and made little impact on the en­ mens or recorded observations of rats from Eni­ vironment; others, through shock, heat, and wetok Atoll are known to exist prior to 1945. radiation waves, destroyed biotic communities Prior to the first test, a biological survey was within several miles of the test sites. The "Mike" made, and J. P. E. Morrison (D. S. National explosion, rated at 10.4 megatons and by far the Museum, personal communication) has indi­ cated that, in 1946 when he visited Eniwetok largest shot undertaken at Eniwetok, obliterated isle~ two islets, carved a crater in the coral reef a he saw only Polynesian rats-on one mile in diameter, and left scorched and singed (Igurin) on which he camped overnight. His plants and animals 14 miles away. observations at Bikini Atoll the same year were As with many operations, code names were much more extensive. Though he observed rats given to each series and shot. The initial test on a number of islets there, he indicated that all program at Eniwetok in 1948 was labeled Sand­ were Polynesian rats. I have examined five spe­ stone; the Greenhouse series followed in 1951. cimens in the National Museum, each collected In 1952 the Mike shot, involving a thermo­ on a different islet, and I concur in the identifi­ nuclear device, was part of the Ivy series. In cation. 1954 the Nectar shot was the principal detona­ A similar, mono-specific rodent infestation tion of the Castle series. The Redwing series in can be cited for other relatively isolated areas in 1956 and the Hardtack series in 1958, both Micronesia prior to World War II or the post­ involving a number of small shots, were the last war period. Thus it seems reasonable to con­ in the test program (Hines, 1962). clude that only Polynesian rats were present at Eniwetok prior to 1946. 1 Adapted from presentation at Second National That an alternative hypothesis can be devel­ Symposium on Radioecology, Ann Arbor, 1967. oped must be admitted. The Japanese had exten­ 2 Department of Biology, Bowling Green State Uni­ versity, Bowling Green, Ohio 43402. Manuscript sive fortifications at Eniwetok Atoll, largely on received September 17, 1968. Engebi, Eniwetok, and Parry islets (Fig. 1). In 265 266 PACIFIC SCIENCE, Vol. XXIII, July 1969

I ENIWETOK ATOLL

N

CHINI[ERO JAPTAN

SOUTHWEST • EAST CHANNEL PASSAGE

NAUTICAL MILES

1012345178 SOUTH CHANNEL

FIG. 1. Map of Eniwetok Atoll. Island names are taken from U. S. Naval Oceanographic Chart 6033 (revised January 1966).

1944 more than 3,500 troops and laborers were a result, the islet was largely denuded, though present on Engebi because of its air strip; Micro­ a palm grove covering nearly one-sixth of the nesians were restricted to the Biijiri, Aomen, islet remained near its center, and some palms Rojoa complex (Hines, 1962:84). Elsewhere in and/or second growth vegetation along the the Pacific, Japanese occupation on occasion lagoon shore and the northwest tip of the islet brought with it the roof rat (Rattus rattus) appear in war-period photographs. Although (Johnson, 1962); this possibility cannot be ex' some palms remained standing after the inva­ eluded here. However, the roof rat populations sion, much of the vegetation was badly shattered now present at Eniwetok Atoll, and the Mar­ (Bryan, 1944). Aerial photographs taken two shalls as a unit, are morphologically similar to months after the invasion show no trees and only the roof rat of the western world (Rattus rattus isolated patches of ground cover. Thus rat habi­ rat/us) rather than to subspecies of the Asian tat was relatively limited. mainland or western Pacific (Rattus rattus man­ In the early test years, no specific observations sorius and other subspecies) (Johnson, 1962 of Eniwetok rats can be found, though reference and personal communication). While post-war is made to a collection of rats on Engebi in 1948 invasions of western roof rats could have and 1949 (Hines, 1962:106). During the Sand­ swamped and replaced earlier introductions, stone series in 1948, one low-yield device was this seems unlikely, considering known inter­ exploded on Engebi on April 15 from a 200­ actions between the two subspecific groups in foot tower. At H + 1 day the gamma radiation the Carolines (Johnson, 1962). in the islet center was estimated roughly at 12 During the Japanese occupation, a major air R/hr; the accumulated dose, at H + 1 yr, 132 R field installation was constructed on Engebi. As (Laboratory of Radiation Biology, University of Rats at Eniwetok-JAcKsoN 267

Washington). Following the test, no exposed cumulated dose was 1,440 R.) The shot caused vegetation remained standing. Of the 43 plant a tidal wave over Engebi, and only stumps of species recorded from Engebi prior to the test, vegetation remained. Rigili islet, 14 miles from only 20 were not exterminated by the blast (St. Mike crater, had plants and birds scorched by John, 1950). thermonuclear heat. The Greenhouse tests in 1951 on Engebi Many observers supposed that rats on Engebi (two detonations) produced an initial gamma had been wiped out by the combined effects of radiation of 6,400-10,000 R in the islet center the 1952 test. But in 1954 rats were found on (Hines, 1962 :210). At H + 1 yr the accumu­ Engebi. This has led to prolonged speculation lated dose was 44 R. But the Polynesian rats (Hines, 1962:207-210). That the Polynesian apparently continued to exist on Engebi, since rat was indeed exterminated by the thermo­ the affected area was small and probably only nuclear test is a possibility. Roof rats perhaps those rats close to the detonation sites were survived, and their numbers may have been killed. supplemented later by individuals from the sup­ Probably about this time, the roof rat (R. ply boats traveling to Engebi. ratttls) was introduced. It may have arrived a The Laboratory of Radiation Biology (LRB) few years earlier at the main supply areas of the records give weights for 75 rats (identified as atoll on ships from the United States or from Polynesian rats) collected on Engebi in 1954. other areas of the Marshalls where it was abun­ Of these, 71 were surely roof rats, as the ani­ dant. But we have no records of observations, mals were far too big (heavy) to be Polynesian and so this statement is conjectural. rats; four were small enough, but no data on In 1952, in preparation for Mike shot (Ivy sexual maturity were given, so that no certain series), rats on Engebi were collected; no radio­ designation is possible. A poorly preserved rem­ activity in their bones was found (Hines, 1962: nant of one of the larger rats has been examined, 151), though slight activity occurred in other and it was a roof rat. tissues (UWFL-33, 1955). Rats were also col­ During the pre-Nectar period in 1954, there lected on Biijiri and Rojoa. All individuals was considerable experimental transportation of were referred to as Polynesian rats. However, rats (all termed Polynesian rats) from Engebi the single Engebi rat for which size data were to adjoining islets. Some 53 rats were involved, recorded (UWFL-33) was obviously not a Poly­ and the investigator (Major C. Barnes, LRB) re­ nesian rat; its weight (175 grams) was too great. cords in his field notes that some of the rats In all probability it was a roof rat. Rats from on Engebi were of a "new gray species." This the other two islets were most likely Polynesian could be taken to indicate that two rat species rats, as judged from their weights (82 grams or were present at this time. I prefer to discount less) . this hypothesis, since the measurements as well A thermonuclear device exploded on Novem­ as two photographs of rats (identified as Poly­ ber 1, 1952, formed Mike crater on the former nesian) show them quite clearly to be roof rats. site of Elugelab and Teiteiripucchi islets, 3 miles No weights or other data from the "gray northeast from Engebi. On November 8, no species" have been found. Irradiation-induced living animals were seen on Engebi; rats, ill and depigmentation (Upton et al., 1960) due to in­ lethargic, were found on Biijiri. On November activation of the follicle pigment cells might 10, six rats were found in traps on Rojoa that explain the appearance of gray animals. had been set on November 7 and had been Following the Nectar detonation of Castle empty on November 8. These two islets are series on May 13 in Mike crater, five rats from approximately 9 miles from Mike crater. (No Engebi (H + 3 days) and twelve from Aram­ size data appear to have been recorded for these biru (H + 4 days) were transported to Bogom­ specimens; the presumption is that they were all bogo. On H + 7 days eight rats were caught on Polynesian rats.) Engebi and transported to Bogombogo. No fur­ The gamma dose rate on Engebi at H + 1 ther notes were made about their survival, and day was 1,000 R/hr; the accumulated dose at no rats have subsequently been trapped on this H + 1 yr, 11,000 R. (At Biijiri the annual ac- islet. On the same day (H + 7), five rats that 268 PACIFIC SCIENCE, Vol. XXIII, July 1969

had severe radiation burns were captured on invasion by swimming was not a possibility. Engebi and returned to the laboratory for pro­ Currents surrounding Engebi are such that rats cessing (Barnes, LRB). No rat collections were could not have crossed from adjoining islets, made after H + 7 days until September and even if these islets had had rats. Exposed reefs October 1954, when six specimens (all of roof at low tide do not provide the necessary path­ rat weight) were logged. Gamma radiation on way between islets. Movement on storm driven Engebi on H + 1 day was 10.7 R/hr; H + 1 flotsam is possible but not considered likely. yr, 118 R (accumulated). As a result of earlier construction activity and In 1955, rats (termed Polynesian) were re­ tests and finally the thermonuclear blast in 1952, ported present on Engebi in tremendous num­ Engebi was stripped of vegetation. The only bers (Hines, 1962:210). Pictures taken in 1957 remaining source of protection would have been of eight rats show that all individuals were roof various construction artifacts, test buildings, rats. The first complete specimens of Engebi rats photographic and instrument bunkers, and cable that we have been able to find were five animals tunnels. Many have assumed that rats which had (originally identified as Polynesian) collected in burrowed under such structures would have 1959 by LRB personnel. These are now in our been sufficiently shielded to permit survival. possession and are quite clearly roof rats. Our The Polynesian rat is not a burrowing animal field studies on Engebi (1964-1968) have but makes a nest under surface vegetation or shown through extensive trapping on the islet debris. The roof rat, while often nesting in that only the roof rat is now present on this much the same way, may burrow. Usually the islet. tunnels we found were adjacent to a concrete wall or slab, or under or adjacent to a coral block or tree root. This kind of physical support ANALYSIS OF RAT SPECIES may be necessary if the burrow walls are not to For a non-mammalogist, the distinction be­ collapse in the friable coral sand. Thus, if any tween these two rat species is not easy. Some rats were to survive a nearby detonation, the differences in size and body and tail proportions roof rat was the likely species. exist, but the pelages may look amazingly alike; Rats are highly adaptable and successful ani­ behavioral aspects may also provide a clue. It mals. While they orient poorly when visual con­ would be very easy for an individual who was tact with land has been broken (while swim­ not looking for species differences to be unaware ming in the lagoon, for example), they often do of the problem. No mammalogists were in­ live in marsh areas and successfully survive volved in any of the field surveys, and, judging seasonal flooding (Steiniger, 1949). Perhaps the from field notes, correspondence, and conversa­ ability of hibernating ground squirrels to survive tions, no one (with the exception of Morrison) early spring floods (Quanstrom, 1966) has some was aware of the rodent species which might parallel in the possible tidal wave survival of be encountered at Eniwetok. Quite clearly, all rats on Engebi. Air trapped in burrows might of the workers expected to find the Polynesian have prevented complete flooding and provided rat. the necessary oxygen supply. I propose that this misidentification has How many could have lived to form the seriously clouded the picture. In the absence nucleus of a new population can only be sur­ of adequate records and specimens, we can only mised, though sufficient protection probably guess about the history of rat populations on the existed for some hundreds of rats. The major atoll. In all probability, the Polynesian rat was limiting factor, after the period of heavy radia­ exterminated by the Mike test in 1952. On the tion, would have been food. Although some re­ strength of a single record, we can hypothesize sprouting of plants occurred within two weeks that the roof rat had been introduced to Engebi and regrowth had begun within two months prior to the 1952 Mike test. Had it been exter­ (Frank G. Lowman, Puerto Rico Nuclear Center minated, the only source of this species on the and LRB, personal communication), until suf­ atoll would have been Eniwetok and Parry islets, ficient vegetation reappeared, the rats would have and perhaps Biijiri and Runit islets; so natural had to exist on beach debris (of which there Rats at Eniwetok-JAcKsoN 269 was probably a considerable amount) and beach Since total land area on Engebi is 260 acres, invertebrates, and by cannibalism. Their omni­ and some scrub areas were present, further vorous food habits make this a reasonable extrapolation to an island population of 10,000 possibility. animals was not difficult (French, 1965). A Not until a year after the Mike test did inten­ current estimate, based on trapping data, sug­ sive preparations start for the Castle series of gests that the population now does not exceed tests, and no observations of flora and fauna on 4,500 rats. Engebi for the intervening period are available. Additional construction and vegetational suc­ Rats could have been transported to Enbegi in cession may have caused a lowered carrying the movement of supplies in early 1954. Field capacity. Lowman's old "rat colony" area is now notes of LRB personnel (especially Barnes) in­ overgrown with Scaevola taccada and T oume­ dicated that rats were relatively common imme­ fortia argentea trees 15-20 feet in height (Figs. diately prior to the Nectar shot in 1954; by 1955 2 and 3). While the airfield remains a grassland the population asymptote probably was being complex, the rest of the islet is covered to approached, for Lowman (LRB) recorded his various degrees by second growth. That the "rat colony" observations during this period sand burr (Cenchrus echinatus) might have been (Hines, 1962 :206-213). Thereafter, the popu­ virtually exterminated by the rats is possible, lation probably declined to the present-day level. since Lowman observed rats frequently feeding Lowman's estimate of the Engebi rat popula­ on the seeds. In 1964 none could be found tion was meant only as an approximation. In an (though in 1966 a few small patches were dis­ area 100 feet square, he saw up to 60 rats at covered). The loss of this single plant species once during the day. Extrapolating to the 15 by intensive feeding might of itself have re­ acres of available grassland yielded an esti­ duced the islet's carrying capacity significantly. mate of 1,000-4,000 rats (Hines, 1962:209). In any event, rats are no longer as abundant as

FIG. 2. Engebi islet viewed looking west toward "Mike" crater (1967). Lowman's rat colony area is just beyond and to the right of the large test building. Remnants of the air strip can be seen on far side of islet. 270 PACIFIC SCIENCE, Vol. XXIII, July 1969

FIG. 3. Vegetation in rat colony area (1965). Shrubs are Tournefortia argentea and Scaevola taccada and are up to 15 feet in height. they were in 1955; rodent actlVlty during the script). Several recent reports are concerned day (prior to late afternoon) and large numbers with the assimilation of radioisotopes by small of rat burrows are not now observed. mammals at the Nevada Test Site (French et aI., 1965; French, 1966; Turner et aI., 1966). Be­ cause of low concentration levels, only temporary RADIATION EFFECTS physiological changes were noted, though con­ For very practical reasons few studies have centrations in specific tissues (e.g., 1-131 in the been able to evaluate radiation-induced popula­ thyroid) did occur. tion changes of rodents under field conditions Laboratory studies (cited by Dunaway and (Dunaway, 1965). Several studies (briefly re­ Kaye, 1964) of the impact of radiation on mam­ viewed by Provost et aI., 1965) have subjected malian reproduction suggest that cumulative individuals to acute radiation and returned them doses above 300 R result in sterility. Except for to their natural environment. Doses below 500­ the Mike shot, estimated annual and accumu­ 750 R generally were ineffective in reducing lated gamma doses (exclusive of prompt radia­ reproductive rates or population size. tion) for rats living on Engebi did not exceed Only one field study under conditions of 132 R (Sandstone). For Nectar the dose was chronic low-level radiation has been reported in 118 R. At daily doses of less than 1 R, some detail. Dunaway and Kaye (1964) evaluated a reproductive cycle disturbances do occur, and cotton rat population living in an area with a partial loss of fertility would by expected at radiation level of 15 mR/hr; no unequivocal ef­ sublethal levels (see Dunaway and Kaye, 1964). fect of radiation on body weight or breeding Certainly any rat caught unprotected above could be demonstrated. Analysis of roof rat data ground by a detonation would have been killed from H. T. Odum's El Verde study in Puerto immediately or in a short time by radiation Rico revealed no change that could be related to effects. The gamma dose above ground during radiation exposure (Jackson, unpublished manu- the first hour ranged from 6,400-10,000 R Rats at Eniwetok-JACKSON 271

(Greenhouse) to 2,800-6,700 R (Mike) to ability of disappearance of 0.4. This figure was a somewhat lower levels in subsequent tests. Ani­ composite of estimates for Polynesian rats on mals protected in burrows were estimated to Ponape in the eastern Caroline Islands (Jackson have received an integrated dose (beta and and Barbehenn, 1962) and Harrison's (1956) gamma) in the nine days following the Mike estimates for the same species in Malaya. On shot of 250-2,500 R; in the week following the this basis, using a litter size of six, the annual Nectar shot, 55-80 R (Hines, 1962:210-211). rate of population multiplication (Ra ) is 7.5 Rats in deeper burrows would have had more (more than twice that calculated by French). protection, but those moving above ground to Following through with calculations and as­ feed would have proportionately increased their sumptions made by French, estimates of sur­ load. Certainly, these estimates provide a basis viving populations necessary to produce the for assuming survival of some individuals, for 1955 estimated population have been mace the LD50 (5 days) for laboratory rats is 800 R (Fig. 5). The interval between shots was 18 (Bond et al., 1965). months; between the 1954 shot and the 1955 obervation, 12 months. French had taken a three-year period; consequently his estimated POPULATION DYNAMICS OF RATS initial populations were actually too small. For At the Hanford symposium, "Radiation and example, where Ra = 4, initial population Terrestrial Ecosystems," French (1965) con­ would have had to be 300, not 150; where Ra = sidered the growth potential and recovery of the 3 (1 Y post-Nectar), Ra = 2.1 (1.5 Y post­ Engebi rat population. Since he assumed ~he Mike), or 1,050 rather than 700 rats. Assume wrong species" based on published sources, his also, as did French, a 50 percent reduced fer­ calculations of reproductive and survival rates tility (multiplication rate) following the Mike were not strictly applicable. In the time period shot; following the Nectar shot, a 25 percent available, could the roof rat have populated reduction. Engebi to the density observed? With these restrictions and assuming that no Let us assume maximal reproductive rates, mortality resulted from the Nectar shot, 250 even though the roof rat population on Engebi survivors of the Mike thermonuclear shot could probably has now stabilized and shows a very have produced a population of 10,000 rats in low level of reproduction. Under conditions of 1955. If no loss of fertility were assumed, only habitat exploitation, high reproductive and low 63 surviving rats would have been necessary. death rates would be expected (Davis, 1951). If a lesser initial population mortality rate Data on the reproduction of Pacific roof rats were assumed (a straight line relationship with are inadequate. Average litter size, for example, 40 percent of the initial cohort remaining after varies considerably. For a different subspecies on 12 months-Fig. 4), an annual multiplication Ponape, the value was 3.8; in Malaya, 5-6. For rate (Ra ) of 11.0 results, and an initial popula­ the same subspecies in temperate regions the tion of only 25 rats is required. With adjust­ litter size was 6-7; in the southern Marshalls ments for reduced fertility-Ra = 8.2 (1 y) ,. (Majuro) in a limited sample, 5 (Jackson, Ra = 5.5 (1.5 y)-an initial population of 961 1962, 1965). In our current Eniwetok studies, animals is indicated (Fig. 5). This initial sur­ litter size has averaged 4.8 (32 pregnancies). As vival rate is only slightly higher than that found an estimate for the increasing Engebi popula­ by P. Q. Tomich (unpublished manuscript) for tion, we used a litter size of six. roof rats in Hawaiian cane fields (mean sur­ Mortality data are even more limited. Harri­ vival: females 8.00 months; males, 6.63. son (1956) cites some data for a similar species months). (R. diardii) in Malaya (Fig. 4), but this is a Rats certainly were killed by the Nectar shot mainland population, and the mortality rates (1954). Most of these estimates require be­ calculated probably are considerably higher than tween 1,000 and 2,000 survivors after this shot" those experienced in an island situation. a figure perhaps not too unreasonable, consider·· Let us assume the same natural mortality esti­ ing the cable tunnels, bunkers, and other pro-· mate used by French (1965)-an annual prob. tected sites available, the relatively low level of 272 PACIFIC SCIENCE, Vol. XXIII, July 1969

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FIG. 4. Survival curves for roof rats (after French, 1965). radiation, and the relatively limited physical Though such survival cannot be actually docu­ damage to the islet-the central area was not mented, the circumstantial evidence strongly sug­ ,covered by the tidal wave. gests that it did occur. Regardless of the rat species designated, re­ population of Engebi by the survivors of the SUMMARY Mike test (1952) was theoretically possible. Indeed, by involving the roof rat with its larger The story of the survival of rats at Eniwetok litter size, even fewer survivors were needed. during the nuclear testing program (1948- Rats at Eniwetok-JACKSON 273

10,000 ~

/ // '(-. // I",y V /17 .....v / /11 ~/ / '11 / ~ V .10/ ff/ / / ~~ IJV V "t /V .(~ / '/II Y ~~. ~ l~~ ~~~ VI / ~ ~I ~ / IpOO '<-, / J. If-o/

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FIG. 5. Initial populations surviving the 1952 "Mike" shot, using several estimates of the annual rate of mul­ tiplication (Ra), required to produce a population of 10,000 roof rats in 1955. 274 PACIFIC SCIENCE, Vol. XXIII, July 1969

1958) is made difficult by taxonomic confusion populations of native rodents. Radiation ef­ and lack of specimens. At best, a hypothetical fects on natural populations, Argonne Na­ reconstruction can be attempted. Early in the test tional Laboratory, pp. 11-18. program at Engebi islet, the Polynesian rat (Rat­ DUNAWAY, PAUL, and S. V. KAYE. 1964. tus exulans) was exterminated, probably by Weights of cotton rats in relation to season, heavy surface radiation. Prior to the detonation breeding, and environmental radioactive con­ of a thermonuclear device in 1952, the roof rat tamination. American Midland Naturalist, (R. rattus) had become established on Engebi, vol. 71, no. 1, pp. 141-155. and a nucleus survived the heavy initial radiation FRENCH, NORMAN R. 1965. Radiation and ani­ by being in deep burrows. Calculations show mal populations: problems, progress, and pro­ that repopulation by the time of the 1954 and jections. Health Physics, vol. 11, pp. 1557­ 1955 observations was theoretically possible. The 1568. decline of the Engebi rat population from its --- 1966. Comparison of radioisotope as­ high density in the mid-fifties probably was a similation by graniverous and herbiverous result of a change in the carrying capacity of the mammals. Proceedings of International Sym­ environment. posium, Stockholm, 25-29 April, 1966, pp. 665-673. FRENCH, NORMAN R., PAGE HAYDEN, and ACKNOWLEDGMENTS THEODORE TAGAMI. 1965. The source of in­ The studies reported here were supported by gested radioactivity in desert rodents. Health the Atomic Energy Commission. A contract to Physics, vol. 11, pp. 637-645. the author (AT(11-1) -1485) provided for field HARRISON, J. 1. 1956. Survival rates of Malayan work in 1965-1967 and for subsequent data rats. Raffles Museum Bulletin, vol. 27, pp. 5­ analysis. Field studies in 1964 were conducted 26. while the author was a member of the Univer­ HINES, NEAL O. 1962. Proving ground. Seattle, sity of Washington Resurvey Expedition to the University of Washington Press. 366 pp. northern Marshalls. The facilities of the Eniwe­ --- 1966. Atoms, nature, and man. USAEC tok Marine Biological Laboratory also supported Division of Technical Information, Oak the field work (1964-68). The Laboratory of Ridge. 57 pp. Radiation Ecology, University of Washington, JACKSON, WILLIAM B. 1962. Reproduction, pp. was of great assistance in providing records, 92-107. In: T. I. Storer, ed., Pacific island data, and specimens. rat ecology. Bishop Museum Bulletin 225. --- 1965. Litter size in relation to latitude in two murid rodents. American Midland LITERATURE CITED Naturalist, vol. 73, no. 1, pp. 245-247. BERRILL, MICHAEL. 1966. Stillness on Eniwe­ JACKSON, WILLIAM B., and KYLE R. BARBE­ tok. Natural History, vol. 75, no. 10, pp. 20­ HENN. 1962. Longevity and mortality, 25. pp. 107-113. In: T. I. Storer, ed., Pacific BOND, VICTOR P., THEODOR M. FLIEDNER, and island rat ecology. Bishop Museum Bulletin JOHN O. ARCHAMBEAU. 1965. Mammalian 225. radiation lethality. New York, Academic JOHNSON, DAVID H. 1962. Rodents and other Press. 340 pp. Micronesian mammals collected, pp. 21-38. BRYAN, EDWIN H., JR. 1944. Revegetation of In: T. I. Storer, ed., Pacific island rat ecology. certain Marshall Islands. Headquarters Cen­ Bishop Museum Bulletin 225. tral Pacific Base Command, mimeograph, 28 PROVOST, E. E., MICHAEL R. PELTON, and pp. FOREST B. KELLOGG. 1965 (1966). The ef­ DAVIS, DAVID E. 1951. The relation between fect of acute gamma irradiation on survival in level of population and pregnancy of Norway feral rodents. Radiation effects on natural rats. Ecology, vol. 32, no. 3, pp. 459-461. populations, Argonne National Laboratory, DUNAWAY, PAUL. 1965 (1966). Problems of pp. 35-39. evaluating consequences of irradiation on QUANSTROM, WALTER Roy. 1966. Flood toler- Rats at Eniwetok-JACKSON 275 ance in Richardson's ground squirrel. Journal jackrabbits after the Sedan Test. Journal of of Mammalogy, vol. 47, no. 2, p. 323. Wildlife Management, vol. 30, no. 2, pp. ST. JOHN, HAROLD. 1950. Flora of Engebi, 433-443. Aomen-Biijiri, and Runit islands, pp. 37-54. UPTON, A. c., A. W. KIMBALL, J. FURTH, K. In: Radiobiological survey of Bikini, Eniwe· W. CHRISTENBERRY, and W. H. BENEDICT. tok, and Likiep atolls, July-August 1949. Ap­ 1960. Some delayed effects of atom-bomb plied Fisheries Laboratory, University of radiations in mice. Cancer Research, vol. 20, Washington (UWFL-23) . no. 8, pp. 1-62. --- 1960. Flora of Eniwetok Atoll. Pacific UWFL-33. 1953. Radiobiological studies at Eni­ Science, vol. 14, no. 4, pp. 313-336. wetok Atoll before and following the Mike STEINIGER, F. 1949. Biologische Beobachtungen shot of November 1952 testing program. Ap­ an freilebenden Wanderratten auf der Hallig plied Fisheries Laboratories, University of Norderoog. Zoologischer Gesellschaft Ver­ Washington. handlungen, vol. 13, pp. 152-156. WOODBURY, ANGUS M. 1962. A review of the TURNER, FREDERICK B., RICHARD H. Row­ ecology of Eniwetok Atoll, Pacific Ocean. In­ LAND, and ROBERT A. WOOD. 1966. Nuclear stitute of Environmental Biological Research, engineering and wildlife: radioactivity in University of Utah, pp. 1-123.