Victoria and Fitzmaurice River Island Surveys

Photo Report

June 2009

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Department of Natural Resources, Environment, the Arts and Sport.

Terry Mahney, Lindley McKay, Kym Brennan and Stuart YoungBiodiversity Unit, Collections, Biodiversity & Biological Parks

The biodiversity Unit of Department of Natural Resources, Environment, the Arts and Sport did wildlife and plant surveys on islands at the mouth of Victoria and Fitzmaurice Rivers from 3rd June to 11th June 2009. This is part of a larger project to survey previously unsurveyed or poorly surveyed islands around the NT coast. Small mammal species are becoming less and less common on the mainland. Islands provide an important place for wildlife to live away from some of the threats, (such as cane toad, cat, pig and fire) that occur on the mainland. These surveys hope to find out which islands are important for wildlife so we can protect them in the future. Department of Defence provided support for the project by permitting us to access islands on Bradshaw Defence lands. They also provided communication support. Special thanks to Kylie Harvey, Lucy McNicol and Peter Watts. Accommodation and helicopter support was provided by Bullo River Station, especially Franz Ranacher. Thanks also to Mel for the biscuits. The Thamarrurr Rangers also helped with the surveys on two islands near the mouth of Fitzmaurice River on Daly River Land Trust. The rangers who came on the trip were Wendy Simon, Maureen Simon, Roseanne Jinjair, Benedict Bunduck and Bobby Munar. We thank them and the traditional owners of the land for their help and allowing us to survey these islands. Also thanks to Thamurrurr coordinators Dan Secombe and Mark Crocombe.

We moved from island to island by helicopter.

There were two survey teams and we visited 8 islands. The survey teams were Terry Mahney and Kym Brennan in one and Lindley McKay and Stuart Young in the other. On each island we had 4 survey sites. Each survey site had 30 elliot traps (small metal traps), 6 cage traps and 3 pitfall traps. Sites were sampled for 2 days and nights. We also counted birds and searched for reptiles and frogs.

Survey Summary Below is a map showing the locations of the islands we surveyed. The islands we surveyed are shown with a red dot. Because some of the islands do not have commonly used names we chose simple names to refer to those that didn’t have names. Previous surveys of these islands were restricted to a 1 night survey of a small island near Vic 1 and a 3 night survey of an island west of Fitz 2.

Below is a summary of what we found:

11 native mammal species and 1 feral mammal (pig); 30 reptile species; 5 frog species including cane toads 81 bird species.

Of these the floodplain monitor (Varanus panoptes) is the only one that is recognised as a threatened species due to the impact cane toads have had on its numbers on the mainland. This was found on Quoin Island. Other interesting or unusual animals included healthy populations of northern bandicoots on Entrance Island, large numbers of pale field rats and accompanying snakes on Quoin Islands, possums on Vic 1 and two species of planigales.

Quoin Island.

On Quoin Island we caught about 125 pale field rats (Rattus tunneyi).

Lots of rats also meant there were lots of snakes. We found carpet python, water python, black whip snake and king brown snake.

We also caught red cheeked dunnart (Sminthopsis virginiae). See photo below. We also caught grassland melomys (Melyomys burtoni) on Quoin Island. This island is a very low lying island with most of it less than 1 metre above sea level. Therefore it is threatened by sea level rises that may occur with climate change as it would go under water. We found cane toads on the northern part of the island which could be a threat to snakes and goannas on the island.

Victoria River Islands – Bradshaw Area Training Facility. There are a number of islands on the tidal flats on Bradshaw. These islands are only separated from the mainland during big tides however they are separated from the mainland by large mud flats which protect the islands from fire and make it hard for pests, such as cats, to cross to the islands. We surveyed 3 of these islands on Bradshaw.

On these islands we found a large number of different small mammal species. This included brush tailed possum (Trichosurus vulpecula), common rock rat (Zyzomys argurus), western chestnut mice (Pseudomys nanus), pale field rat and planigales (Planigale sp., to be confirmed).

Photograph of planigale from Bradshaw Islands. We caught 2 different species of planigales.

Photograph of Western Chestnut mouse. These islands had a high number of small mammal species. This may be due to the fact that the vegetation on these islands is long unburnt and provides good shelter and food for these animals. Cane toads were found on some of the islands and what was possibly cat prints were found in one location. At one site feral honey bees had forced a possum out of its hollow.

Entrance Island Entrance Island is a relatively large rocky island about 40 kilometres upstream from the mouth of the Victoria River. Northern brown bandicoot (Isoodon macrourus) were very common on this island. Their diggings could be found anywhere on the island where there was soil that they could dig in. We caught 7 in traps. We also caught another species of planigale.

This island was also long unburnt. As result the vegetation was interesting with a species of Acacia (Acacia kellerii) being common in the rocky areas. This Acacia is more commonly found in the north Kimberley and is at the eastern limit of its range near the Victoria River. We also found a few cane toads on this island.

Photograph showing a site dominated by Acacia kelleri shrubs.

Fitzmaurice River Islands – Daly River Aboriginal Land Trust We also surveyed 2 islands on the tidal flats of the Fitzmaurice River on Daly River Aboriginal Land Trust.

The Thamurrurr Rangers from Port Keats helped us with the surveys on this island.

Photo: Roseanne, Wendy and Maureen showing mud muscles they collected from the mangroves.

The only mammal we caught on these islands was a western chestnut mouse. It’s uncertain why there were fewer mammals on these islands, however there were pig tracks and diggings around the islands and cat tracks in the mud. We found cane toads on these islands as well.

Photo: Thamarrurr Rangers Benedict and Roseanne.

Plants

The botanical highlight of the survey was finding a small fleshy plant growing on salt flats. Its scientific name is Hemichroa diandra. It is a low spreading perennial herb with pale green succulent leaves and small pink flowers. It was found on both Quoin Island and Entrance Island. It is special because these records are the first from coastal areas in the NT. All other NT records are from around salt lakes in central Australia.

Photo: Hemichroa diandra During the survey some shrubby wattles (Acacias) were found that are rare in the NT. They include: Acacia setulifera, Acacia froggattii, and Acacia kellerii. Acacia kelleri and Acacia froggatti were found on Entrance Island and Acacia setulifera was found on Vic 1. In the NT these three wattles are found in the rugged sandstone country of the lower Victoria River district (eg Bradshaw).

Photo: Acacia kellerii Photo: Acacia froggattii Acacia kelleri and Acacia setulifera are listed as threatened species. The important thing about these wattles is their vulnerability to frequent fire. The shrubs are killed by fire but new plants grow from seed in the soil. However if successive fires occur before they have produced new pods and replenished the seed bank, local extinction can occur. It takes about 8 to 15 years before they produce enough seeds to maintain healthy populations.

Threats and Management Implications The islands at the mouths of the Victoria and Fitzmaurice Rivers had a large variety of mammal species. Because of their isolation from the mainland, either by water or tidal flats, many of them do not get burnt very often. This may help explain the reason why there was a good variety of small mammals when, on the mainland, their numbers are decreasing. These islands provide a useful example of how the plants and animals survive when places are rarely burnt. As such, land owners and managers might want to maintain these islands in their unburnt state. In some cases there are similar “islands” that are joined by only a small sliver of land over which fire sometimes burns. Careful use of fire would also help maintain these areas as long unburnt areas as well. During the survey it was observed that the mainland adjacent to the islands on the Bradshaw training area and Wadeye Aboriginal Land Trust had been extensively and heavily burnt. Frequent burning of extensive sandstone areas is likely to have a detrimental impact on the diversity of native plants and animals that make this area biologically special. A patchwork (mosaic) approach to fire management (with regard to appropriate frequency and season) would be more beneficial for the environmental values of the area. Cat, pig and cane toad were also recorded on some of the islands. The presence of cane toads may explain the absence of northern quolls. Pig and cat numbers appear to be relatively low due to the islands’ isolation and lack of permanent water. This may also help explain the good numbers of native mammals. The large and healthy population of pale field rats and accompanying snake species on Quoin Island are at substantial risk from sea level rise as most of the island is less than 1 metre above high tide.

Species List

Site location Common name Scientific name Quoin Vic 1 Vic 2 Vic 3 Entrance Fitz 1 Fitz 2

mammals brush tailed possum Trichosurus vulpecula x (2) echidna Tachyglossus aculeatus x scats planigale Planigale sp 1 x (2) x (1) planigale Planigale sp 2 x (1) red cheeked dunnart Sminthopsis virginiae x (3) northern brown bandicoot Isoodon macrourus x (11) western chestnut mouse Pseudomys nanus x (1) x (1) X (1) common rock rat Zyzomys argurus X (11) pale field rat Rattus tunneyi X (151) x (1) black flying fox Pteropus alecto x dingo Canis lupis dingo x track pig Sus scrofa x track reptiles Saltwater crocodile Crocodylus porosus x track Bynoe’s gecko Heteronotia binoei x x x Bynoe's Prickly Gecko Heteronotia planiceps x Northern dtella (gecko) Gehyra australis x x X x Northern spotted rock dtella (gecko) Gehyra nana x x Spiny tailed gecko Strophorus ciliaris x Zig zag gecko Oedura rhombifer x x Slender rainbow skink Carlia gracilis x Two spined rainbow skink Carlia amax x x x x x x Skink Cryptoblepharus sp? x x x x x

Site location Common name Scientific name Quoin Vic 1 Vic 2 Vic 3 Entrance Fitz 1 Fitz 2

Noble snake eye skink Cryptoblepharus exochus x Arboreal snake eyed skink Cryptoblepharus

plagiocephalus x

Plain ctenotus (striped skink) Ctenotus inornatus x x x x Smooth tailed skink Glaphyromorphus isolepsis x x x Robust ctenotus (striped skink) Ctenotus robustus x Rusty topped delma (legless lizard) Delma borea x x x Black necked snake lizard Delma tincta x Griffin’s lerista Lerista griffini x Grey’s menetia (skink) Menetia greyii x x Main’s menetia (skink) Menetia mainii x Red tailed snake eyed skink Morethia ruficauda x Slender snake eyed skink Proablephurus tenius x x x Frilled lizard Chlamydosaurus kingii x Yellow spotted monitor (goanna) Varanus panoptes x Gilbert’s dragon Lophognathus gilberti x Water python Liasis mackloti x x Carpet python Morelia spilota x Northern small eyed snake Cryptophis pallidiceps x Black whip snake Demansia vestigiata x King brown snake Pseudechis australis x amphibians Marbled frog Limnodynastes convexiusculus x Rocket frog Litoria nasuta x Wotjulum frog Litoria wotjulumensis x toadlet Uperoleia sp x

Site location Common name Scientific name Quoin Vic 1 Vic 2 Vic 3 Entrance Fitz 1 Fitz 2

Cane toad Rhinella marinus x x x birds arafura fantail x x x australian bustard x bar shouldered dove x x x x x x barn owl x bar breasted honeyeater black eared cuckoo x x x black shouldered kite x black faced cuckoo shrike x x x blue winged kookaburra x x boobook owl x x x brahminy kite x brolga x brown falcon x x broad billed flycatcher x brown goshawk x x x brown honeyeater x x x x x brown quail x x bush thick knee x x chestnut rail x collared sparrowhawk x x diamond dove x x double bar finch x x x x fairy martin x x x golden headed cisticola x x x

Site location Common name Scientific name Quoin Vic 1 Vic 2 Vic 3 Entrance Fitz 1 Fitz 2

great bowerbird x x x green backed gerygone x grey butcherbird x x grey crowned babbler x x x grey shrike thrush x x x x x x hooded robin x x jabiru x jacky winter x leaden flycatcher x x x x little bronze cuckoo x little friarbird x little woodswallow x x x x x long tailed finch x x mangrove gerygone x x x mangrove kingfisher x x mangrove golden whistler x x masked lapwing x mistletoe bird x x x x x x x northern fantail x x x x x northern rosella x x owlet nightjar x x pallid cuckoo x x peaceful dove x x x x x pheasant coucal x x pied butcherbird x x x x rainbow bee-eater x x x x x x rainbow lorikeet x

Site location Common name Scientific name Quoin Vic 1 Vic 2 Vic 3 Entrance Fitz 1 Fitz 2

red backed button quail x red backed fairy wren x x x x x x red browed pardalote x red headed honeyeater x red winged parrot x x x x red tailed black cockatoo x x x restless flycatcher x x rufous whistler x x x x x x x silver crowned friarbird x shining flycatcher x spotted harrier x spotted nightjar x x striated pardalote x x x tawny frogmouth x torresian crow x x x tree martin x x variegated fairy wren x varied sitella x x weebill x x wedge tailed eagle x whistling kite x x white bellied cuckoo shrike x x x x white breasted sea eagle x x white breasted woodswallow x white gaped honeyeater x x x white throated gerygone x x white throated honeyeater x

Site location Common name Scientific name Quoin Vic 1 Vic 2 Vic 3 Entrance Fitz 1 Fitz 2

willy wagtail x x x x x x x yellow white eye x x x yellow tinted honeyeater x x x x