Appraising vertebrate diversity of Bonapart Islands, Kimberley, Western Australia

2006·5 MB·English

by  Ric Howe

APPRAISING VERTEBRATE DIVERSITY ON
BONAPARTE ISLANDS, KIMBERLEY, WESTERN
AUSTRALIA
By RICHOW
Western Australian Museum, Locked Bag 49, Welshpool DC, WA 6986
LINC SCHMITT
School of Anatomy and Human Biology, The University of Western
Australia, Crawley, WA 6009
ROY TEALE
Biota Environmental Sciences, 14 View Street, North Perth, WA 6006
and MARK COWAN
CALM, Hannan Street, Kalgoorlie, WA 6430
ABSTRACT
Three expeditions examining 35 islands in the Bonaparte
Archipelago along the northwest Kimberley coast were
undertaken between August 2002 and June 2005. These
documented numerous new records of mammal and reptile
species for the islands with the fauna of 27 islands being
examined for the first time. Mammals were usually
confined to the larger islands adjacent to the mainland and
only on East Montalivet and Coronation were populations
recorded on more distant islands. Two mammal species were
trapped on an unnamed island that was only 23 ha in
extent. Reptiles occurred on all islands examined from the
smallest (4ha Low Rocks) to the largest (18121 ha Bigge
Island). The 29 reptile species recorded represent several new
records for the Bonaparte Archipelago and includes new
localities for many species. Populations of Olive Pythons
were recorded on islands as small as 73ha. No frogs were
recorded although climatic conditions and the poor wet
seasons preceding the expeditions were not conducive to
amphibian activity.
INTRODUCTION Pleistocene glacial maximum at
Kimberley islands have been about 18 000 years before
isolated from the mainland for present (Nix and Kalma 1972,
up to 10 000 years as a result of Hopper et al. 1996). Such
increasing sea levels after the last extended periods of isolation of
92
islands elsewhere has lead to Kabay and Burbidge 1977;
many populations differ¬ Kitchener 1978; Burbidge and
entiating into new taxa as McKenzie 1978; Western
evidenced by the islands of the Australian Museum 1981) added
Indonesian archipelago, lying substantially to our under¬
immediately to the north of the standing of the distribution of
Kimberley coast (Schmitt et al. the north Kimberley vertebrate
1995, Kitchener and Suyanto fauna. These surveys lead to a far
1996), Pi 1 bar a coastal islands better understanding of the
(Abbott and Burbidge 1995, composition, habitat preferences
Smith 1976) and Bernier, Dorre and biogeography (McKenzie
and the Houtman Abrolhos off 1981) of most vertebrate groups
the west coast (Ride and of this tropical area, particularly
Tyndale-Biscoe 1962; How et al. mammals, and permitted a
2004). reappraisal of the taxonomy of
numerous species (Kitchener and
The documentation of the
Humphreys 1986, Kitchener and
mammals, birds, amphibians, and
Sanson 1978, Kitchener and
reptiles of the Kimberley region
Caputi 1988, Kitchener 1976,1989,
of Western Australia has pro¬
Storr 1975). The major rainforest
gressed at very different rates.
survey of the late 1980s
Storr (1980) regarded the quarter
century beginning in 1886 as the (McKenzie et al. 1991) and
continued sampling activity in
‘golden age’ of Kimberley
the region has shown that the
ornithology. All but a few of the
area covered by the 1:250 000
birds now known from the
map sheets of Cambridge Gulf,
region were made known to
Montague Sound and Prince
science in that period. The first,
Regent in the north Kimberley
and relatively complete, list of
are the richest for frogs,
mammals from the Kimberley
mammals and reptiles in all
was compiled by Dahl (1897)
Western Australia (How and
within two decades of the first
Cowan 2006).
European exploration of the
region. While our understanding In contrast, the fauna of
of the diversity of the birds and Kimberley islands is poorly
mammals of the Kimberley was documented and there has been
largely complete by the end of only one published survey of
the 19th Century, an under¬ these islands (Burbidge and
standing of the herpetofauna McKenzie 1978). This reported on
had barely begun. Most of the some 20 islands in the Bonaparte
herpetofauna was described in Archipelagos of the northwest
the 20th Century and over a third Kimberley that were surveyed for
has been described since 1960. between 1 and 11 days. Islands in
the Buccaneer Archipelago in the
The extensive array of biological
west Kimberley were also
surveys conducted during the
surveyed by government
1970’s (Miles and Burbidge 1975;
93
biologists briefly between 1980 species level, from populations on
and 1982 and results remain the adjacent mainland. All
mostly un-published (but see endemic insular taxa are
Abbott and Burbidge 1995), recognised as threatened fauna
however, the fauna of Koolan either by legislation (Government
Island, also in the Buccaneer of Western Australia 2005) or by
archipelago, has been Department of Conservation and
documented in detail by Land Management authorities
McKenzie et ai (1995). Information under the Priority Species List.
gathered on these island surveys, This paper reports on the
later visitations by individuals outcomes of three expeditions to
and the major rainforest survey 35 Kimberley islands in the
(McKenzie et al. 1991) as well as Bonaparte Archipelago under¬
specimens in the collections of taken between August 2002 and
the Western Australian Museum, June 2005. These surveys were
indicate that at least 5 frog, 34 designed to make collections and
mammal and 58 reptile species are
document the frogs, mammals
present on the offshore islands
and reptiles from selected islands
along the Kimberley coast. This is in order to determine the
in marked contrast with the 26 morphological and genetic
frogs, 72 mammals and 109 attributes of island and main¬
reptiles known from adjacent land populations. These studies
areas of the mainland. None of will permit an evaluation of the
the offshore island populations systematic status of many insular
have been examined systemati¬ populations and contrast these
cally and all populations, except data with published information
Ramphotyphlops sp. and Lerista available on vertebrates from
praefrontalis, have been referred to cognate archipelagos off the
mainland taxa in published Pilbara and west coast of Western
reports. Australia. The project will also
Our understanding of the appraise the evolutionary pro¬
identity of vertebrate faunas on cesses involved in differentiating
the Kimberley islands also stands island forms and assist in
in sharp contrast with the determining whether popu¬
detailed knowledge of island lations are relictual or derived
archipelagos off the Pilbara and from colonisers from adjacent
western and southern coasts of islands or the mainland.
Western Australia, all of which
have been separated from the
ISLANDS AND METHODS
mainland for similar periods of
time. Many of Western Australia's Islands were selected on the basis
more southern islands have of their geographic location with
vertebrate populations that are islands representing those both
distinctive at the subspecific distant from and adjacent to the
level, and in some cases at the mainland being selected.
94
I Zt’MTE IZS’V 125’,WE I26F-
9
5

P-< CM.18 ^3 O 1. Map of island and mainland locations sampled during the survey of the Bonaparte Archipelago between 2002 and
Likewise, islands of different Previously assessed distributional
sizes were selected as well as those data for the amphibians, reptiles
consisting of the main sandstone, and mammals were obtained
volcanic or laterite geological from the literature (Burbidge
substrates. Wherever possible, a and McKenzie 1978; Abbott and
wide variety of vegetation types Burbidge 1995) and the State's
were sampled on each island collections housed in the WA
with both woodlands and vine Museum.
forest being targeted.
General rainfall and climate
Thirty-five islands were patterns in the northwest
examined over the three Kimberley are presented in
expeditions along with two Burbidge and McKenzie (1978), an
locations on the mainland; one area characterized typically by a
with three sites adjacent to Scott ‘wet’ season extending from
Strait during the June 2004 December to April and a 'dry'
survey, the other with three sites season from May to November.
opposite Glauert and Boongaree Rainfall averages over 1500mm
Islands, during the June 2005 at Mitchell Plateau and is
survey. For each of these concentrated in the ‘wet’ season.
locations, the data for the sites During the present expeditions,
have been aggregated. the wet season of early 2002 was
one of the driest on record, and
The islands sampled are shown in
those for 2004 and 2005 were
Figure 1, while their area, broad
also well below average.
geographical co-ordinates,
principal geological formations The charter vessel 'Barra B’ was
and duration of sampling are used as a base for visitation to all
presented in Table 1. Nine of the islands sampled. Access to the
islands sampled during this islands was by outboard
project [South West Osborn, runabout and predicated by both
Middle Osborn, Carlia, Low shoreline type, weather
Rocks, East Montalivet, South conditions and tidal activity that
Maret, Bigge, Coronation, ranged up to ten metres.
Boongaree] were also sampled in
the early 1970s (Burbidge and
SAMPLING
McKenzie 1978) with specific
information on their geology, Sampling occurred on three
vegetation and vertebrate fauna separate expeditions between 25
presented then. On South West August - 6 September 2002, 26
Osborn, Bigge and Boongaree May - 8 June 2004 and 19 May - 3
Islands, sampling during this June 2005.
survey was carried out on both On each island where one or more
volcanic and sandstone nights trapping occurred (Table 1),
substrates, while on Carlia Island sample sites were trapped using a
only sandstone substrates were line of between 20 and 25 Elliott
sampled. Type A traps, baited with
96
universal bait. These were set collected, Litoria copelcindi, L.
around 10 metres apart. A few meiriana, both from the
Elliott Type B traps were used on mainland on Prince Regent
some lines and wire mesh Nature Reserve adjacent to
Tomahawk cat traps were also Glauert Island. None of the
employed where sampling islands examined had frogs
continued for several days and present and a general lack of
there was the prospect of catching freestanding water on the vast
larger mammals. Traps were majority of islands and the 'poor'
checked during the morning each wet seasons associated with the
day. No concerted effort was made sampling time probably account
to trap bats by mist netting or for this low documentation of
harp trapping. Opportunistic amphibians.
collecting of vertebrates was
Previous surveys have identified
undertaken on all islands visited
four species of frog in the
and involved active searching in
Bonaparte Archipelago, Notaden
litter and dead wood as well as
weigeli, Litoria rubella and L.
under rocks and logs. Head-
inermis from Bigge Island and
torching for nocturnal species was
Cyclorana sp. from Katers Island
conducted on several islands and
(Smith and Johnstone 1978).
small pitfall traps were employed
Frogs are particularly poor
on Cassini, Descartes, North Maret,
survivors on small islands and
Buffon Islands and the mainland
ineffective dispersers across sea-
opposite Scott Strait.
barriers.
Voucher specimens were taken
of all taxa for use in later
analyses of morphological and MAMMALS
genetic variation of vertebrates Mammals were collected from 11
from the Bonaparte archipelago. of the islands and the two
Numerous individuals, particu¬ mainland locations during the
larly mammals, were released survey (Table 2). In total, 394
after weighing and removal of individuals of twelve species
tail or ear tip for later genetic were captured and identified.
examination. The sighting of a small rock
wallaby on Boongaree Island
probably represents the
RESULTS AND DISCUSSION
previously recorded and
Sampling on the islands and collected Petrogale burbidgei, while
adjacent mainland sites during scats and diggings of echidna,
the three expeditions Tachyglossus aculeatus, were very
documented 2 amphibian, 12 common on Boongaree but only
mammal and 29 reptile species. one positive sighting was made.
None of the species recorded by
AMPHIBIANS this project are new records for
Two species of frogs were mammals on the Bonaparte
97
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part of the island.
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Table 2. Mammal ind2002-2005 and the c C<«uCQO/Dv) . -rv^OU<Sbe-*u3o QVts-~3>o*-' f3|coO “t3O£2fo23toc: £at<OoU -^2c3S©oto ^.£|VE<2^- c<3du COEa$OsJ Zyzomys argurus Pteropus scapulatus Vespadelus douglasoru Taphozousgeorgianus
100
Kimberley and occurs on several Kimberley islands may have
larger near-shore islands (Abbott influenced the distribution of
and Burbidge 1995). During the the two species of Zyzomys’
current expeditions there were (McKenzie et al. 1978).
six instances of the Northern
The survey of the Bonaparte
Quoll being captured in traps
Archipelago in the early 1970s
with partially eaten rodent
(McKenzie et al. 1978) recorded 22
species that indicate the quolls
native mammal species from 20
entered the traps in order to eat
islands. Foremost amongst the
the rodent. The rodents involved
islands for mammal diversity was
were Rattus tunneyi, Zyzomys Augustus Island, the largest, on
argurus and Z. woodwardi. which 11 species were recorded,
Larger islands generally had more while Bigge had eight species and
species while smaller islands Boongaree nine. Although six
usually lacked mammal days were spent sampling on
populations, although of Bigge during the present project,
particular interest is the only two species of mammal
discovery of two mammal species were recorded (Table 2). No
on 'unnamed' island in Scott attempt was made to
Straight. This island is just over systematically sample bats
23 hectares and its ability to throughout the expeditions and
support both Rattus tunneyi and these accounted for 5 of the
Mesembriomys macrurus is native species recorded by
surprising. Four islands with McKenzie et al. (1978).
mammal species, Carlia,
There has been continuing
Boongaree, Capstan and
interest in the extinction rates of
Purrungku, are separated from
Australian mammal species in
the mainland by less than 100
the temperate and arid areas of
metres of water and the latter
the continent. It has been
two may be connected to the
postulated that mammals in a
mainland at extreme spring low
‘critical weight range' of 35g-
tides. It is remarkable that a
5.5kg have higher extinction
population of Zyzomys was found rates than those outside this
on East Montalivet, given its
range (Burbidge and McKenzie
large distance from the mainland
1989). However, mammals that
(30 km), as there appears little
are both smaller and larger than
likelihood that this population
those in the ‘critical weight
represents anything other than a
range’ do not appear to persist
long-isolated relictual one.
well on offshore Kimberley
Augustus Island is the only
Islands. The North Kimberley
offshore location where both
bioregion of Western Australia is
species of Zyzomys co-occur and one of the few areas where the
gives credence to the statement
original mammal fauna remains
that ‘Wetter conditions at the
intact with no recorded
time of isolation of the
extinctions. Excluding bats and
101