the amethystine python

ECOLOGICA Photo: Alastair Freeman

A STUDY IN POWER AND GRACE THE AMETHYSTINE PYTHON

Herpetologist Alastair Freeman tracks Australia’s largest land predator.

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mpressively sleek and with a healthy sheen, the snake raised the top third of her body over a tree buttress and then wound up into the canopy. ‘Shiny’, as my daughter had taken to calling her, was an amethystine python that I had grabbed the previous evening as she was about to slide through an open door into our chicken coop. A couple of tense minutes followed as I tried to stuff a reluctant, but thankfully calm, bundle of muscle and sharp teeth into a large reptile bag. My intent was not to remove her from the yard, but to take a good look, measure her and insert a PIT tag so that she could be identified again. At just over 3 metres, she was longer than average but nowhere near the 6 or perhaps 8 metres these pythons can grow to. I hoped she would stay. For a herpetologist nothing beats having a large predatory reptile in your backyard, and this species is not only our biggest snake but the largest land predator too. The encounter with Shiny and my daughter’s newfound interest in snakes, arising out of a recently acquired pet python, have revived for me a long-term fascination with big snakes.

Australia’s pythons Pythons are an ancient group living in Africa, Asia and the Australian-New Guinea region. Australia is considered the world centre for python diversity, with 15 species, more than a third of those known. This was once thought to indicate that the family arose in Australia (during Gondwanan times), but recent

DNA work suggests the ancestors evolved on the large northern continent of Laurasia. New species are still being described, particularly in South East Asia and parts of Melanesia, so Australia’s distinction of having the most diverse python fauna may be lost in the future. Many Australian python species are small, less than 1.5 metres long. The amethystine (or scrub) python (Simalia kinghorni) is our longest, with a confirmed maximum of 5.6 metres. Individuals longer than 8 metres have been reported, and I think this may be possible, although extremely rare. The other Australian giant is the olive python (Liasis olivaceus). It doesn’t grow as long, but is bulkier and could be Australia’s heaviest snake. Both are impressive by global standards but smaller than Asia’s reticulated python (Python reticulatus), the African rock python (Python sebae) and the Indian rock python (Python molurus). The physical differences between Australia’s two biggest snakes reflect their ecology. The olive python inhabits rock outcrops and floodplains in northern Australia, and is seldom seen off the ground, while the amethystine python with its long tail and relatively slender build is like an oversized tree snake, a perception reinforced by its agility. It is found in Queensland along the east coast, north from the Conway ranges in the Whitsundays. In Torres Strait, it is replaced by the Papua New Guinea form (Simalia amethistina), although the boundary between the two is unknown. wildlife-australia.org | Wildlife Australia | 27

The amethystine pythons on Milman Island, east of Cape York, are a classic case of island dwarfism, growing no longer than 2.5 metres. There is not enough prey on the island for a very large snake. Photo: Alastair Freeman

One island east of Cape York has ‘midget’ amethystine pythons. No longer than 2.5 metres, and most weighing less than 1 kilogram, they are a classic example of ‘island dwarfism’. Milman Island is less than hospitable for a large predatory snake, having little in the way of substantial prey. The first pythons washed up on the island, or stranded there by rising seas, were probably a normal size, but over generations they have shrunk on a diet of lizards, crabs and the odd bird. We don’t know if their small size is now genetically programmed or if, with a good feed, they could grow to a ‘normal’ size.

forest floor. Temperatures are significantly higher in and above the canopy than below. Some of the pythons we tracked had favourite epiphytes they returned to for basking weeks or months after vacating them at the end of winter.. A lack of epiphytes may explain the absence of amethystine pythons in some parts of the Atherton Tablelands despite apparently suitable habitat. We were not the first to report this preference. In the late 1800s Swedish explorer Carl Lumholtz described how in winter on the Atherton Tablelands his Aboriginal guides would climb, sometimes ‘fifty to sixty yards’, to catch pythons in ferns. Baked python was a delicacy. Although Lumholtz called the snakes Morelia variegata, judging by their size (more than ‘20 feet’) they could only have been amethystine pythons. One of the male pythons we tracked had neck injuries consistent with fighting. In winter they sometimes congregate in open sunny areas, where males engage in combat, presumably to win mates. Mating pairs have been seen at these sites.

An ecologically influential predator

Amethystine pythons are both active foragers and sit-and-wait predators. More than once we saw our radio-tracked snakes in classic ambush pose next to wallaby trails in long grass in an old orchard. At other times we watched them move along the forest floor, sticking their head down holes and crevices, tongue flicking, tasting the air. As befits a large reptilian carnivore, their diet is catholic, ranging from rats to tree kangaroos, and chickens to Tracking amethystines small birds. Younger snakes tend to eat more ectothermic (cold blooded) prey while adults consume larger mammals. Big snakes are challenging subjects for research – they are typically sparse in the landscape and often difficult to capture One question I am often asked is whether amethystine pythons and handle. They also tend to be rare in ever prey on humans. We know that pythons museum collections because they are too (and boas) can eat prey up to about their large to fit in standard specimen jars, and own weight, and there are records of other Big snakes are take up lots of costly storage space. This species eating or attempting to eat humans. challenging subjects means that little is known about most large The heaviest amethystine I have recorded was pythons. The first substantial ecological study just over 20 kilograms (and 4.5 metres long), for research. on amethystine pythons was published only a which would put predation of children within decade ago. the realms of possibility. However, I haven’t heard of any cases. Perhaps our upright stance and the relatively At about this time Amanda Freeman (my ornithologist wife) small head and gracile build of the amethystine python make us and I conducted a study on their habitat preferences. Through too difficult to catch and eat. the generosity of Australian Geographic and Andrew Krockenberger of James Cook University, we were able to put radio transmitters On the Atherton Tablelands, circumstantial evidence suggests in six amethystine pythons captured at the Centre for Rainforest that amethystine pythons suppress densities of browsing leaf Studies on the southern Atherton Tablelands. Because eaters such as possums and pademelons, particularly in forest transmitters cannot be attached to snakes externally, they have fragments. Researchers in South America studying islands to be surgically inserted into the body cavity just forward of the created by a dam found dramatic changes to vegetation as vent. We were lucky to have a friendly local vet, Wendy Bergan, the disappearance of predators permitted high densities of who loved working on wildlife and was happy to insert and remove transmitters for the cost of materials. From 2004 for the next two and a half years we tracked six pythons for varying lengths of time in an area of rainforest, wattle regrowth, sclerophyll forest and pasture. From this we learned that the amethystine python is naturally a forest species, with 82% of our sightings in rainforest or rainforest regrowth, far exceeding the proportional availability of these habitats. Their preferences differ from those of their cousins, the carpet pythons (Morelia spilota), which are found in all habitats across the study area. Their home ranges varied from 20 to over 200 hectares. Because of this great variation it is hard to define a typical home range size. Diamond python males near Sydney use a home range of around 45 hectares while females use about half that. Despite their size, most amethystine python didn’t move far in a day. However, one male we followed moved over 800 metres in a 24 hour period. One of our most interesting findings was that during the cool, misty and often wet winters the pythons spend most of their time in large epiphytic basket ferns (Drynaria species) high up in or above the canopy. These large ferns, some over a metre wide, make an ideal basking platform above the cool gloom of the 28 | Wildlife Australia | SPRING 2016

ECOLOGICA

The tracking study on the Atherton Tableland found that amethystine pythons are a rainforest snake. They also turn up in urban areas, mainly in roofs, but invariably close to forest. During winter they spend most of their time in large epiphytic basket ferns (right), an ideal platform for sun basking. Photos: Alastair Freeman

herbivores. I have often wondered if the same thing has occurred in rainforest fragments on the Atherton Tablelands which have lost their largest predator, the amethystine python. Testing this by moving pythons would be an exercise fraught with difficulty. However, this may happen of its own accord. Since the late 1990s community groups and the Queensland National Parks and Wildlife Service have been planting a corridor between Curtain Fig National Park (a remnant of endangered rainforest noted for high densities of tree kangaroos and possums, with no amethystine pythons), and Lake Eacham, part of Crater Lakes National Park (a remnant with ample amethystine pythons, and not noted for high densities of leaf-eaters). If, as I suspect will happen, amethystine pythons use this planted corridor to move between the two remnants, Curtain Fig may end up with fewer marsupials and changes to vegetation. We can only assume this would represent a more natural condition.

Not to be ignored Amethystine pythons have lost habitat, particularly on the coast south of the Daintree River. But they are almost certainly more common in remaining habitats, as the level of persecution and hunting is far lower than at any other time since humans arrived in Australia. Much of their habitat, particularly in the Wet Tropics, is in national parks or reserves. Unlike the carpet snake, the amethystine python is seldom killed on roads, suggesting they are reluctant to cross them.

The main threat to the species may be disease. Inclusion body disease, thought to be due to a retrovirus, has been recorded in captive pythons overseas and in Australia. How it is transmitted is unknown, but it is always fatal. It hasn’t been recorded in wild snakes but the potential for spread into the wild cannot be dismissed, whether through the accidental or deliberate dumping of an infected snake or some other vector transmitting the disease from captive to wild animals. A few amethystine pythons are kept in captivity, particularly in Australian zoos, but they are not popular in the pet trade, presumably because of their size. They also have a reputation for aggression and a bad attitude. However, I have found that, as with other pythons, the belligerence of wild amethystine pythons varies between individuals and circumstances. Perhaps, in captivity their muscularity and litheness are intimidating. When people talk of Australia’s iconic wildlife, the amethystine python is seldom mentioned, despite being our largest land predator. I defy anyone who has watched one glide through the forest not to be awed by their grace and power. ALASTAIR FREEMAN has lived and worked in the Wet Tropics for nearly 20 years. A professional herpetologist by vocation, much of his spare time is also spent ‘herping’, although he has also been known to chase the odd little brown bird with his ornithologist wife, Amanda. Tropical rainforest is his preferred habitat, although he does make the odd excursion into the tropical savannahs.

For the tracking study, a transmitter was surgically inserted into the body cavity of each python and then removed after the study by a veterinarian. The largest python measured during the study (left),, a female of relaxed disposition, was 4.5 metres long and weighed 20 kilograms. Photos: Alastair Freeman

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