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Gotta catch ’em all – Top End Trapping

By Jack Ashby, on 21 April 2011

A delayed account of zoological fieldwork in Australia – Part 12

Burton's snake lizard

Burton’s snake lizard from a funnel trap

From April 2010 I spent about five months undertaking several zoological field projects across Australia. I worked with government agencies, universities and NGOs on conservation and ecology studies ranging from Tasmanian devil facial tumour disease, the effect of fire, rain and introduced predators on desert ecology and how to poison cats. This series of blog posts is a delayed account of my time in the field.

Weeks Sixteen to Nineteen – part 1

For my final bit of fieldwork I joined a team of ecologists from the Australian Wildlife Conservancy (AWC) at one of their sanctuaries, carved out of the incredible Arnhem Land Plateau in the monsoonal forest of the Northern Territory’s Top End.

This is the fourth year of the study here. The early aim is to determine the diversity of the region, and this can then be used to determine how changes in the use and management of the land affect things in the future. Some of our data will be used as a baseline to determine what happens to biodiversity when they exclude cattle from parts of the reserve (it is still run as a cattle station to maintain its lease requirements and raise a bit of cash).

The traps we used were pitfall traps on drift-net fences, like those I described in the Simpson Desert, Elliot traps (baited boxes with trap-doors for small mammals), cage traps (baited cages with trap-doors for larger mammals) and funnel traps. Funnel traps are a bit like a lobster pot on it’s side with a way in on both ends. As animals run along a drift fence, they enter the outer opening, which narrows in to a raised inner opening. Upon entering this they drop into the main chamber and can’t see the way out. These are the best way of catching snakes.

Larger animals are monitored with a couple of different systems of studying footprints on sand pads. Birds were recorded incidentally, and every study site had an in depth habitat assessment and full botanical survey.

Digging traps

For each of the sites we would have to dig the pits and fences into the rock-hard clay. The land here floods every wet season, and then the oven-like temperatures of the dry season bake the clay like it was in a kiln. This makes digging pretty hard going. It helped to wet the soil with water, but every time I went to the creek to fetch some I would hear and see splashes from the crocodiles jumping in. Mostly they were harmless freshwater crocs, but the dangerous saltwater crocs are in the area too, mainly in the main channels, and if you don’t see the species that made the splash in the black water it does put you a little on edge when filling buckets or having a wash. A 2.5m bull shark was seen here too, even though we’re over 100 miles inland.

How we trapped things

Measuring a common planigale

Measuring a common planigale

The trapping sites have a 200m long square perimeter, unless it’s on a river in which case the sites runs 80m along the bank, by 20m wide. Elliot traps baited with peanut-butter and oat balls line the edge, and cage traps go in the corners. In the middle is a massive T-shaped drift fence with pitfall traps at the middle and each end. Funnel traps are positioned along the fences.

Each night for three nights all traps would be opened and baited. The pits and funnels were left open in the day time to catch reptiles active in the day, but the metal cages and Elliots were emptied and closed early each morning so that no animals cooked in the heat of the day. They were checked every morning (all traps) and evening (pits and funnels only).

We caught hundreds of lizards, snakes, frogs and cane toads (more about them next week), and just a handful of mammals. Identifications and measurements were made and recorded. Animals were marked impermanently so that we’d know if we caught them more than once in a trapping cycle. Genetic samples were taken of the few mammals we caught, which is crucial as some groups – particularly the planigales – are being completely taxonomically overhauled .

We were concentrating on the small, ground-dwelling diversity of the region. As someone who has always put nearly all my energy into studying mammals, in a way it was refreshing to go somewhere where I barely set eyes on a small furry thing. It gave me the opportunity to investigate the scaleys and slimies as the key ecological factors in a region.

Strophurus ciliatus

A gecko which wiggled out of my hand and up my arm (Strophurus ciliatus)

Next week I’ll be discussing one of the main reasons why there are no mammals here – the disastrous, disgusting, destructive cane toad.


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