CSIRO PUBLISHING
Australian Mammalogy, 2012, 34, 55–58 http://dx.doi.org/10.1071/AM11004
Unforeseen consequences of a misidentified rodent: case study from the Archipelago of the Recherche, Western Australia Andrew A. Burbidge A,G, Ian Abbott B, Sarah Comer C, Emma Adams D, Oliver Berry E and Kate E. PenwardenF A
87 Rosedale Street, Floreat, WA 6014, Australia. 1 Caddy Avenue, West Leederville, WA 6007, Australia. C Department of Environment and Conservation, 120 Albany Highway, Albany, WA 6330, Australia. D Department of Environment and Conservation, 92 Dempster Street, Esperance, WA 6450, Australia. E CSIRO Marine and Atmospheric Research, Private Mail Bag 5, Wembley, WA 6913, Australia and Invasive Animals Cooperative Research Centre/School of Animal Biology, The University of Western Australia, Crawley, WA 6009, Australia. F School of Animal Biology, The University of Western Australia, Crawley, WA 6009, Australia. G Corresponding author. Email:
[email protected] B
Abstract. Since 1953, it has been assumed that Rattus rattus occurred on Woody Island, Archipelago of the Recherche, Western Australia, and that R. fuscipes was locally extinct. Recent trapping and identification, including sequencing of mitochondrial DNA, has confirmed the persistence of R. fuscipes. The apparent misidentification of the 1950 specimen and failure to collect vouchers since has led to unforeseen consequences, including a proposal to eradicate the Rattus population. Additional keywords: Rattus rattus, Rattus fuscipes, voucher specimens, Woody Island. Received 3 February 2011, accepted 21 June 2011, published online 7 November 2011
Introduction Several authors have noted that the introduced black rat, Rattus rattus, occurred on Woody Island, the seventh largest of the 348 islands and rocks constituting the Archipelago of the Recherche (Goodsell et al. 1976; Abbott and Black 1978; Abbott 1981; Whisson and Morris 1992; Abbott and Burbidge 1995; Burbidge and Manly 2002), and that the native southern bush rat (or mootit), R. fuscipes, had become locally extinct there. All of these records seem to be based on Serventy (1953), who stated: ‘Ship Rat, Rattus rattus alexandrinus (Geoffroy, 1803). An individual of this introduced species was dug out of a burrow on Woody Island when digging for petrels, two lizards being found in the same burrow. It was identified by Mr. L. Glauert. [Ludwig Glauert (1879–1963) was Curator, later Director, of the Western Australian Museum from 1927 to 1956.] N.E. Stewart informs me that Ship Rats were very troublesome on Woody Island when he visited it in 1939. He killed twenty-three with a stick around the campfire. Dead specimens were found on Boxer and North Twin Peak.’ (p. 45). The specimen referred to by Serventy cannot now be located; indeed, there is no specimen of any Rattus sp. from Woody Island in the Western Australian Museum (WAM) (Kitchener and Journal compilation Ó Australian Mammal Society 2012
Vicker 1981; Dr R. How, pers. comm.). It is unclear whether any mammal specimens were collected during the 1950 Australian Geographical Society Expedition to the Archipelago of the Recherche as Serventy (1953) states ‘The study of the mammals of the Recherche Archipelago was confined to field observations, no collecting being done on these island reserves.’ (p. 40). R. fuscipes was known from 11 islands along the south coast of Western Australia, eight of these being in the Archipelago of the Recherche (Abbott and Burbidge 1995; plus two pick-up skulls WAM M51312 and M55267 from Middle Island found in 1976). Recent surveys by the Department of Environment and Conservation (DEC) have recorded it on an additional three Recherche islands (Glennie, Goose and Wickham) but failed to locate it on Middle Island. Eight specimens of R. fuscipes were trapped on Woody Island in 1921 (Hull 1922) and lodged in the Australian Museum, Sydney (registration numbers M3113 to M3120, Dr S. Ingleby, pers. comm.). Taylor and Horner (1973) examined M3113 and M3114 during their revision of Australian Rattus and included them in R. f. fuscipes. In January 2010 the National Trust of Australia WA’s Gabbie Kylie Foundation (a foundation established to conserve www.publish.csiro.au/journals/am
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and interpret the Indigenous heritage values of the south coast region of Western Australia) was granted funds from the Commonwealth Government’s Caring for Our Country Community Action Grants scheme to eradicate black rats on Woody Island. As part of this project some initial trapping was carried out to confirm the presence of the black rats. A few specimens were captured and images sent to DEC, where the rats were identified as most likely to be R. fuscipes. As a result, the proposed eradication project was halted. Materials and methods In August 2010, DEC staff (S. Butler and EA) carried out a brief fauna survey on the island to determine the presence and distribution of R. fuscipes and R. rattus. Twenty medium Elliott traps were set over four nights, distributed from the coast to the summit of the island. Also in August 2010, two of us (OB and KEP) visited Woody Island to collect rats for research into the tolerance of native mammals to the toxin 1080. Eight Rattus were captured, identified in the field as R. fuscipes on the basis of nipple count, foot pads and tail length (Cooper 1994) and returned live to The University of Western Australia. The mitochondrial cytochrome c oxidase subunit I gene in the Woody Island rats was sequenced (Penwarden 2010). Results Thirty-four Rattus were caught during the DEC August 2010 trapping session. All were identified in the field as R. fuscipes. Hair samples were taken from several of the Rattus and analysis (Brunner and Triggs 2002) using the DEC South Coast field reference collection confirmed all samples to be R. fuscipes. The mean weight of the Woody Island R. fuscipes was 106 g (range 76–138 g), the mean snout–vent length was 129.3 mm (range 115.6–146.1 mm) and mean tail length was 141.2 mm (range 123–152.3 mm). Voucher specimens from Woody Island will be lodged in the Western Australian Museum. Sequencing of the mitochondrial cytochrome c oxidase subunit I gene in the Woody Island rats collected by OB and KEP confirmed that all the Woody Island rats captured were R. fuscipes (Penwarden 2010). Discussion The deleterious effects of introduced R. rattus on island floras and faunas are well documented, with many extinctions of birds, and with native rodents having also been displaced (Harris 2009). In at least one case, Christmas Island, extinction of two endemic Rattus spp. was caused by a murid trypanosome transmitted by R. rattus (Wyatt et al. 2008). The probability of R. fuscipes surviving in abundance after more than 60 years of cohabiting with R. rattus seems remote. The question then arises – did R. rattus ever occur on Woody Island? The possibility that Serventy’s animal was misidentified by Glauert is supported by Serventy’s (1953) statement that dead R. rattus were also found on North Twin Peak and Boxer Islands. A series of R. fuscipes (WAM M14758–14773) was collected at North Twin Peak Island by Kabay and Start (undated) in 1976, who stated that there was no evidence of the R. rattus reported by
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Serventy (1953). A 2009 survey of North Twin Peak Island coordinated by DEC confirmed the persistence of R. fuscipes. Small reptiles (two species of geckos and five of skinks) were ‘very common’ or ‘common’ on Woody Island in 1986 (Maryan and Robinson 1987). Such abundance is unlikely had R. rattus been present. Studies from New Zealand islands of the impacts of introduced rats (Kiore, R. exulans) are suggestive of local extinction of some reptile species and reduced abundance and reproduction of others (Crook 1973; Whitaker 1973; Towns et al. 1997). Furthermore, the small, burrowing white-faced stormpetrel, Pelagodroma marina, breeds on Woody Island (Lane 1984). R. rattus is notorious for extirpating small burrowing seabirds from islands it has invaded (Towns et al. 2006). Alternatively, R. rattus could have occurred on Woody Island at the time of Serventy’s visit in 1950, but did not survive, possibly because of the presence of poison pea, Gastrolobium bilobum. R. fuscipes is tolerant to the toxin sodium fluoroacetate (1080) that occurs in Gastrolobium spp. (Mead et al. 1985; Twigg and King 1991). Opportunities for the accidental introduction of Rattus rattus to Woody Island have been numerous, so Serventy’s (1953) record of this species did not surprise. First, navigators cruised the archipelago in rat-infested ships in 1818 (King 1827: 10, 278, 324, 345). Sealers and whalers were active in the archipelago in the 1820s (Béchervaise 1954) and 1837 (Dickson 2007), and the black rat was doubtless present on ships (Abbott 2008). Second, from at least ~1879 until ~1958 sheep (Ovis aries) were grazed on the island, with a half mile (800 m) long fence erected to separate the grassy eastern end from the scrub with poison pea to the west (Department of Conservation and Land Management (CALM) file vol. 3 folio 102; Hull 1922; Willis 1953; The West Australian 16.ix.1896: 2; 27.iv.1904: 8; and 15.xi.1950: 20). Goats (Capra aegagrus hircus) were also present in 1956 (CALM file vol. 3 folio 49). It is likely that the island was visited at least biannually for the purpose of landing and removing sheep. Third, Woody Island has often been disturbed, with frequent burning (The West Australian 27.iv.1904: 8) to provide nutritious feed for sheep, and less frequent fires that were sufficiently intense to be seen at night from Esperance (The West Australian 22.iii.1935: 16; 11.ii.1950: 5) and burn much of the vegetation (Willis 1953). Finally, in 1972 the Western Australian Wildlife Authority (a predecessor of the current Conservation Commission of Western Australia) approved a request for Woody Island to be used for tourism. A wharf to which vessels could be secured was constructed in 1973 (CALM file vol. 2 folio 190), facilitating possible entry of black rats onto the island. This narrative reinforces the necessity and importance of collecting voucher specimens of mammals and for museums to retain vouchers (Baynes 1972; Baynes et al. 1987; Kitchener 1992; Ellis 1995), including of presumed introduced animals, especially from places that are infrequently visited and difficult to access, like many islands. If Serventy’s specimen had been retained by a museum and voucher specimens of the Rattus captured by Goodsell et al. (1976) and Whisson and Morris (1992) had been taken and added to a museum collection, reports of the occurrence of R. rattus and local extinction of R. fuscipes on Woody Island since 1950 would not have been written, and the proposal to eradicate what turned out to be an indigenous species would not have arisen. It is also possible that the extensive
Unforeseen consequences of a misidentified rodent
development of tourist facilities (jetty, walk trails, camping area, visitor centre and accommodation) on the island since 1999 would not have occurred to the same degree. This is because in 1982 the Western Australian Wildlife Authority cited the occurrence on Woody Island of the black rat as one of the reasons for making the island available for tourist development (CALM file vol. 1 folio 113, 182). The presence of a jetty and tourist facilities on Woody Island increases the risk of introduction of non-indigenous species and indicates the need for the preparation and implementation of a biosecurity plan. The only introduced mammal now known from Woody Island is the western grey kangaroo, Macropus fuliginosus (Goodsell et al. 1976; Abbott and Black 1978), a few of which still occur there (EA, pers. obs). Goodsell et al. (1976) also trapped a Pseudomys, identified by them as P. albocinereus. A sketch of this animal is provided in their report but no voucher specimen was collected. Whisson and Morris (1992) pointed out that the animal could be P. occidentalis; their trapping on Woody Island in April 1992 resulted in no captures of a Pseudomys, but numerous captures of a Rattus identified in the field as R. rattus (46 captures in 490 trap-nights). Recent trapping by DEC and by OB and KEP (Penwarden 2010) also did not detect any Pseudomys. As many mammals are being identified in the field and released without vouchers being lodged in a recognised collection, there is a need for taxonomists to provide easily-used characters that can be used in the field to identify difficult groups. Cooper (1994) is an example. Digital photography, for example of foot pads in rodents, can assist in confirming field identifications. These aids, however, are not a sufficient substitute for voucher specimens, which are even more important for difficult-to-identify species and for records outside known ranges. In conclusion, this paper emphasises the necessity for biologists to collect representative specimens and to deposit these in a recognised institution. Many young ecologists mistakenly presume that these actions are no longer required, and some express a reluctance to euthanase animals for vouchering. Molecular studies are currently revolutionising our knowledge of population variation and not all species limits, even of mammals, can be regarded as definitively settled. In addition, some ethics committees discourage collection of specimens and require approval in advance of species deemed appropriate for collection (thus hindering any opportunistic collecting). While we deplore indiscriminate collecting, we think that it is the professional prerogative of scientists to validate their identifications by vouchering specimens for later assessment.
Acknowledgements AAB thanks Dr Nicola Mitchell for drawing his attention to OB and KEP’s identification of Woody Island Rattus. We thank Louisa Bell (DEC Albany) for identifying the hair samples. Work conducted by DEC South Coast Region in the Archipelago of the Recherche is covered by DEC Animal Ethics Committee permit 24/2008. OB and KEP’s research was approved under The University of Western Australia’s Animal Ethics Committee permit RA/3/100/956, Department of Environment and Conservation Regulation 17 licence SF007600 and DEC Regulation 4 authority CE002941. KEP and OB thank the UWA Faculty of Natural and Agricultural Sciences Startup Grant Scheme for support.
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