The population of rock wallabies (genus Petrogale) on Oahu, Hawaii

Biological Conservation 30 (1984) 99-108

The Population of Rock Wallabies (Genus Oahu, Hawaii

Petrogale) on

James D. Lazell, Jr The Conservation Agency, 8 Swinburne Street, Conanicut Island, RI 02835, USA

Timothy W. Sutterfield Division of Forestry and Wildlife, Honolulu, HI 96813, USA

&

William D. Giezentanner Massachusetts Audubon Society, Lincoln, MA 01773, USA

ABSTRACT d population of peculiar rock wallabies (Macropodidae." Petrogale) became established in the Ko'olau Range, Oahu, in 1916. The few available specimens differ f r o m known Australian forms in skull characters, size, and electrophoretic profile. The population seems largely confined to ca 7.0 ha in one valley f r o m ca 150-400 m, on a mean slope of 60 °. There were ca 53 (range 27-94, p = 0.05) individuals in a grid of l.5 ha, indicating a population o f 247 (126-439) animals. The sex ratio was 1:3 males:females. Fifty per cent o f females over 89 cm were carrying or nursing joeys during November. Seemingly old, blind, postreproductive individuals o f both sexes were present and all individuals appeared robust. There was no significant size difference between the sexes. The taxonomic status o f these animals is under study. 99 Biol. Conserv. 0006-3207/84/$03.00 © Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain

100 James D. Lazell, Jr, Timothy W. Sunerfield, William D. Giezentanner

A population of rock wallabies has been resident in the Ko'olau Range of Oahu since the successful escape of a pair in August 1916 (Tomich, 1969; Kramer, 1971). The members of this population differ from all known Australian rock wallabies in coloration and cranial features (Lazell, 1980) as well as size and electrophoretic profile (Lazell, 1981). They share their karyotype only with Petrogale p. penicillata, from which they differ strikingly in other respects (Sharman et al., 1978; Lazell, 1981; Table 1). Petrogale p. penicillata is not today a common animal in Australia, JDL travelled to Australia in 1979 and 1981, and examined ca 200 Petrogale in five museums. Of these, 16 were adults of nominate penicillata. The purpose of our study was to assay population parameters for the Oahu colony and determine the feasibility of further specimen collecting.

METHODS State of Hawaii permit 82-08 was issued on 1 October 1981 for a livecapture, mark, release, and recapture census. Ten standard box traps (two single door, eight double door) were situated in a grid roughly 60 x 80 m. Traps were baited with various fruits, including cantaloupe, avocado, guava, and lilikoi (passionfruit); the last was most successful. Traps were checked twice daily, between 0600-0800h and 1530-1730 h and usually rebaited. Animals (except pouch young) were marked with numbered yellow plastic ear tags: males in right ear, females in left. Total length, tail, hindfoot, and ear (notch) were measured; the animals were weighed and photographed (in colour). Pouch young may be reproducing members of the population within a year (Johnson, 1979). The habitat seems to be restricted to the Ewa Kalihi valley between 150-400 m, and extends a linear distance of only ca 1 km (Lauret, 1982). The habitat is a series of sheer cliffs and narrow ledges with a mean slope, calculated from the USGS topographic quad, of 60 °. Mapping the habitat required photography from a helicopter (TWS) at an angle normal to the mean slope (Fig. 1). The photographs were projected onto a plane surface and habitats were mapped directly in the same manner as standard aerial photos are used to prepare vegetation maps. Areas were then measured. This method provides a meaningful area calculation because it provides a measurement of the available surface area on the cliff face.

Fig. 1. Sketch map view of the Oahu rock wallaby habitat in the Ko'olau Range prepared from photographs taken from a helicopter (TWS) at an elevation of 673 m, 590 m southeast of the foot of the cliff, at an angle normal to the mean slope of 60 °. Best habitat was judged by frequency of sightings and presence of scats.

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102 James D. Lazell, Jr, Timothy W. Sutterfield, William D. Giezentanner

The habitat is trisected by narrow ravines which facilitated our approach to the cliffs and ledges. Traps were placed in accordance with four characteristics of station location in this order of priority: accessibility to us; shelter for wallabies during inclement weather; apparent frequent use by wallabies (based on sightings and scats); and position relative to other traps in the grid. Thus, trap stations 1-4 were clustered within a 30 m strip along one ledge, while station l0 was c a 80 m distant (vertically), and 29 m from station 9 (horizontally) (Fig. 1). Care was taken that trapped animals would be sheltered from rain because it apparently causes them severe discomfort to get wet (Kramer, 1971, and personal observations). In estimating the size of the resultant grid we measured relative trap positions with a 50 m foresters' tape. We elected to use 40 m as an appropriate radius for trap effectiveness because this was about the same as the average travel distance and one-half the maximum travel distance, both procedures accepted by Otis e t al. (1978). We calculated our grid as 1.5 ha. We realize that mapping and grid size determination in the habitat of this rock wallaby could easily be carried into realms of abstruse topology, but we believe the methods we have used provide conservative area and population estimates. Trapping commenced 4 November and terminated 23 November 1981. Heavy rain caused us to prop the traps open with sticks (they were left baited) on 17 and 18 November. We totalled 126 trap-nights. Animals are referred to below by ear tag number, preceded by F for females and M for males.

RESULTS We captured 20 individuals, c a one per six trap-nights, including four pouch young. The latter measured c a 50-300 ram; we did not attempt to sex any but the largest, which was a male. We obtained 12 recaptures, including three of the females with pouch young. These are noteworthy because of the behaviour of mothers carrying young. The aboriginal survival strategy of the rock wallaby on Oahu may be paraphrased from Kramer (1971): throw away the baby and jump off the cliff. This strategy was not employed by F69 or F70 carrying 100 and 50 mm young, respectively, quite firmly attached to nipples (F69 was recaptured with her joey still in place six days after initial capture). However, F73 and F78, carrying young c a 150 and 300 mm respectively, both jettisoned their

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TABLE 1 Seven Morphometric Comparisons between Petrogale p. penicillata, of New South Wales and southeastern Queensland, and Oahu Petrogale. (Only specimens with fully erupted dentition have been used. Males show absolute distinction with respect to every character tabulated. Females show some overlap in all characters except condylobasal length: see text. Colour characters are given in Lazell (1981).)

MALE Total length Tail Hindfoot Condylobasal length Molariform row Palatal vacuity Pelage length FEMALE Total length Tail Hindfoot Condylobasal length Molariform row Palatal vacuity Pelage length

P. p. penicillata (mm)

N

Oahu (ram)

N

1 209 (1 189-1 230) 633 (603-665) 172 (166-179) 109 (104-113) 32.8 (31-4-35.3) 17-4 (16.6-19-4) 31 (25 35)

2 2 2 7 7 6 6

I 027 (1 000-1 055) 516 (515-518) 149 (143-155) 102 30-7 13.8 20

3 3 3 1 1 1 1

1 072 (950-1 129) 549 (500-597) 155 (145-165) 104 (98-109) 32.1 (31-1-33.2) 16.4 (14.9-18.0) 26 (15-34)

5 4 4 9 9 8 6

979 (890-1010) 493 (470-520) 145 (133-147) 97 31.7 15.2 15

9 9 9 1 1 1 1

joeys on removal from the traps. After tagging, measuring, and weighing the females, thejoeys were returned to the pouch in each case; the females were held in an upright position for a few moments prior to release and directed along the ledges. That neither jettisoned her joey a second time, and that both joeys rediscovered nipples, was demonstrated by recapture: F73 was recaptured after six days and F78 after three days; the joeys were doing well in both cases. Sixteen adults are tabulated in Table 1; recaptured individuals are tabulated in Table 2. Two individuals in the population, F76 and M77, appeared to be very old. The female, F76, was apparently entirely blind in the left eye (opaque white) and the right eye was cloudy. She had all four nipples roughly the same size; none was enlarged enough to indicate recent reproduction. She may have been a sterile intersex (Sharman et al., 1970); perhaps she was

104 James D. Lazell, Jr, Timothy IV. Sutterfield, William D. Giezentanner TABLE 2 Some Characteristics of the Population Sample of Rock Wallabies in 1.5 ha in November 1981. (Three of the adult females had unsexed pouch young < 200 mm total length.)

Males Females

Adults

Subadults (800 mm TL)

Joeys (300-755 mm TL)

Maximum travel (m)

Average travel (m)

2 8

2 2

2 1

78 68

42 35

post-reproductive and her nipples had rescinded. This was the palest specimen seen. She was ashy-grey dorsally, with white hairs so dense that even the characteristic sooty shoulder patch was of subdued contrast. Some buff remained in the rump pelage, and her forearms were rust-red. Interestingly her ventrolateral stripe was bold and sooty, extending prominently from wrist, across elbow, through axilla, and on to the groin. For a striking comparison see the colour photograph of Australian P. p. p e n i c i l l a t a provided by Kirsch (1977). A big male, M77, was apparently blind in the right eye (opaque white); the left eye seemed clear. He was also pale, with a greater ashy dorsal overlay than is typical. His testes measured 26mm; those of M56 measured 33. Another male we regarded as definitely subadult (measurements 965,475,145, 59) had 25 mm testes. It is possible that M77 was also post-reproductive. Both of these seemingly old individuals appeared in robust good health (apart from their cataracts). We never caught any individual in the same trap twice. Males travelled 20-78 (av. 42) m between recaptures. The record is held by M56, who, with three recaptures, was caught more often than any other individual. Females travelled 16-68 (av. 35) m between recaptures; F69 (with a ca 10cm joey) holds the distance record, but F67, apparently resident above station 1, was caught most often and recaptured twice. There was no significant difference in travel distances between the sexes. We have used the Lincoln Index as presented by Overton (1971) to calculate 53 (95 % confidence limits 27-94) individuals in our grid. We believe this indicates a population of 247 (95 ~o confidence limits 126--439) animals on the Ewa Kalihi cliffs. We are aware of the caveats of Mares et al. (1980) with respect to number of recaptures needed to establish home range, and make no claim to have yet determined a home range. We have carefully considered the seven models presented by Otis et al. (1978), but

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have no evidence at present that would allow us to adopt any of them but the first, which is an idealized Lincoln Index. Of our total of 32 captures, 31 occurred in the night trapping period, ca 1730-0600 h. Only one individual, F67, was caught once in a day trapping period (ca 0800-1530 h), and she was caught a total of three times. The animals are regularly active during the day, however (Kramer, 1971, and numerous personal observations). We do not know why animals seemed reluctant to enter our traps during the day. Local residents report that activity away from the cliff sites is largely nocturnal.

DISCUSSION The movements of rock wallabies away from the cliff habitat is problematical. We have found tracks on the dirt road along the top of the ridge. Local residents at the foot of the cliff report periodic incursions of wallabies into the yard area and onto the roofs of the buildings. We believe activity concentration is crepuscular (as did Kramer, 1971) or nocturnal. Local opinion is that wallabies leave the cliffs to obtain food. Kramer (1971) studied the diet of this population in some detail and Lazell (1980) commented on two staples: ulei Osteomeles anthylliforia (Rosaceae) and Christmas berry or Brazilian pepperbush Schinus terebinthifolia (Anacardiaceae), both abundant on the cliffs and ledges. There may be a limit to the amount of pepperbush the wallabies can utilize because of its high toxicity to most herbivores (Hegnauer, 1964; Morton, 1976). There may also be a correlation between consumption of this anacard and novel liver enzymes (Lazell, 1981). Wallabies have been reported in other valleys of the Ko'olau Range (Kramer, 1971; Lauret, 1982). However, Lauret (1982) made a diligent effort to verify these reports with no success. He concluded that a combination of moisture and accessibility to men and dogs rendered 17 other cliff areas surveyed unsuitable for, at least unused by, wallabies in the first five months of 1981. Lauret (1982) felt that individuals dispersing from the Ewa Kalihi population might be short-term residents at some of these sites and might account for the reported sightings. All of the museum specimens except Bishop Museum (BBM) 157473-4 (which were purposefully collected) are subadults. Two, BBM 147113 and Brigham Young University, Hawaii (BYUH) 456, were found dead on the

106 James D. Lazell, Jr, Timothy W. Sutterfield, William D. Giezentanner Likelike Highway in the Kalihi Valley. One of these, the male BYUH 456, was found 1.6 km east of the colony site by Lauret, 13 March 1981. Two additional specimens, BBM 145185 and 145201, were killed by dogs in the Kalihi Valley (on the Ewa side of Kalihi Stream). The sole remaining skin and skull, BBM 156645, has no locality data beyond Oahu and was donated by the Division of Forestry and Wildlife. These few data accord with the view that significant departure from the main colony site is by dispersing youngsters. Pick-up skeletal material, e.g. BYUH 346 and 460-1, is of variously aged animals from joeys (dentary BYUH 346 with only the second molar erupted) to old adults (dentary BYUH 461 with all teeth worn to the pulp). All of this material is from the foot of the cliffs at the colony site. Only further study will reveal which animals move greater distances from their residence sites, whether such movement is regular, and how far the individuals travel. Our observations led us to believe that at least some animals, e.g. F67, M77, F68, and M71, lived in the areas where we trapped them. That we failed to trap all the animals living within a close radius of our stations was demonstrated repeatedly; for example, on our last full day of trapping, 22 November, we caught five individuals, only two of which (F78 and her joey of ca 30cm) were recaptures. We additionally saw two uncaught animals, M71 and an untagged youngster on the ledge at station 4 (which trap held F80). If the driest and most secure residence sites are held by adult individuals, then the high reproductive rates documented by this study and Kramer (1971) would result in considerable outward dispersal. If resident adults grow old and sexually senescent at their residence sites, we cannot envisage harm to the colony resulting from judicious removal of old adults for museum specimens.

CONCLUSIONS The Oahu rock wallaby population is fecund and more populous than previously estimated by Kramer (1971) or Lazell (1980). It does appear, however, that the only viable colony is at Ewa Kalihi (Lauret, 1982). The size and colour distinctions from Petrogale penicillata noted by Lazell (1980, 1981) were confirmed and augmented by new data. We plan to continue to monitor this population regularly. We recommend the permitting of tightly controlled harvest of old adults

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timed to coincide with the convenience of our Australian colleagues so that maximal use can be made of every specimen removed for anatomical, biochemical, and physiological studies. We recommend that State-owned property at the colony site be managed in a way most beneficial to the wallabies. For example, feral dogs should be periodically trapped out. We further recommend a cooperative land management programme with the US Army, which owns the ridge above the colony site inside Fort Shafter.

ACKNOWLEDGEMENTS Drs Geoffrey B. Sharman and David Briscoe, Macquarie University, Gerry M. Maynes, University of New South Wales, and Ian D. Hume, University of New England--all in NSW, Australia--have aided us in numerous aspects of comparison of the Oahu animals with Australian Petrogale. Sharman travelled to Hawaii to participate in field work (with JDL) in 1980. Ronald L. Walker, Ralph Saito, Timothy Burr, and Marie Morin, all in the Wildlife Branch, Division of Forestry and Wildlife, Hawaii, assisted us in numerous ways. Dr Alan Ziegler and the staff of the Bernice Bishop Museum have prepared specimens, stored frozen tissues, and aided with the literature. Gary D. Moniz, mammalogist, and Gail Wine, Honolulu Zoo, supplied ear tags, instructions, and assistance in the field. Michael Lauret has worked closely with us, often in the field. Aline Hermann, Jan Soderquist, and Steven Sipman also assisted us in the field. Without the hospitality and generosity of the Slaughter family of Aiea this project would never have been conceived or pursued.

REFERENCES Hegnauer, R. (1964). Chemotaxonomie der Pflanzen, 3(12): Anacardiaceae. Basel, Birkhauser Verlag. Johnson, P. M. (1979). Reproduction in the plain rock-wallaby, Petrogale penicillata inornata Gould, in captivity, with age estimation of the pouch young. Austr. Wildl. Res., 6, 1-4. Kirsch, J. A. W. (1977). The six percent solution:second thoughts on the adaptedness of the Marsupialia. Am. Scient., 65, 276--88. Kramer, R. J. (1971). Hawaiian land mammals. Rutland, Vermont, Charles E. Tuttle.

108 James D. Lazell, Jr, Timothy W. Sutterfield, William D. Giezentanner Lauret, M. (1982). The distribution of brush-tailed rock wallaby Petrogale penicillata, on Oahu. 'Elepaio, J. Hawaiian Audubon Soc., Honolulu, 43(4), 25-7. Lazell, J. D. (1980). Kalihi rock wallaby of Hawaii. Tigerpaper, UN-FAO Bangkok, 7(2), 31-2. Lazell. J. D. (1981). Strange rock wallabies of Oahu. Explorers Journal, 52(2), 66-7. Mares, M. A., Willig, M. R. & Bitar, N. A. (1980). Home range size in eastern chipmunks, Tamias striatus, as a function of number of captures: statistical biases of inadequate sampling. J. Mammal, 61,661-9. Morton, J. F. (1976). Pestiferous spread of many ornamental and fruit species in South Florida. Proc. Fla State hort. Soc., 89, 348-53. Otis, D. L., Burnham, K. D., White, G. C. & Anderson, D. R. (1978). Statistical inference from capture data on closed animal populations. Wildl. Monogr., 62, 1-135. Overton, W. S. (1971). Estimating the numbers of animals in wildlife populations. In Wildlife management techniques, ed by R. H. Giles, 403-55. Washington, The Wildlife Society. Sharman, G. B., Robinson, E. S., Walton, S. M. & Berger, R. J. (1970). Sex chromosomes and reproductive anatomy of some intersexual marsupials. J. Reprod. Fert., 21, 57-68. Sharman, G. B., Briscoe, D. A. & Maynes, G. M. (1978). Petrogale. In The status of the Australian Macropodidae, ed by W. E. Poole, 19-22. Adelaide, Royal Zoological Society of South Australia. Tomich, P. Q. (1969). Mammals in Hawaii. Bernice P. Bishop Mus. Spec. Pubis, 57, 16-19.