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AUSTRALIAN BROADCASTING CORPORATION 02 December 04 Pythons join the Rat Race
Across Australia's north the first heavy rains of the oncoming wet season are triggering a unique migration of predator and prey. With sun-baked floodplains now filling with water, thousands of native rats are leaving their shelter among cracks and crevices to make a necessary journey to higher ground. Following them, are huge and hungry water pythons with little else but rat on their menu.
Dusky rats and water pythons are the two dominant animals on coastal river floodplains in northern Australia. Their populations have evolved a mutual relationship, finely balanced to ensure ultimate survival and even flourishing of each species.
In some of the Top End's floodplains there are so many rats that it is one of the highest known herbivore densities in the world. In a good year there are as many as100,000 rats per square kilometre, or one for every 10 square metres. That's more than the total biomass of most large herbivorous animals of the African savannahs. Without some means of population control the rats would eat themselves into extinction.
The water pythons are even more amazingly successful. It was once thought that the Serengeti plains in Africa had the densest predator rating. Predators there, including lions, tigers and cheetahs, weigh in at 30 kilos per square kilometre. But at a density of around 300 kilos per square kilometre, the pythons surpass that figure by a factor of ten. At Fogg Dam on the Adelaide River, where conditions are ideal for breeding, the python density has been as high as 850 kilos per square kilometre.
Scientists Ric Shine and Tom Madsen from the University of Sydney have spent fourteen years trapping and studying dusky rats and water pythons on the Adelaide River, about 60 km east of Darwin. They say this is the only known seasonal migration in the world where scaly reptiles follow their prey.
Water pythons will eat pretty much any small animal, but in the Northern Territory 95% of their diet is the dusky rat. When the rats start leaving for higher ground there's no choice but to follow.
Living together in the dry
During the dry season, from around May, hundreds of thousands of dusky rats live and breed in the treeless and cracking floodplains of the Top End's rivers. The cracks in these clay soils can be as deep as one and a half metres. The water pythons live close by. Water pythons are actually misnamed - though they can live in water for up to a year at a time, many of them also live on the dried out floodplain, close to their favourite prey, the dusky rat.
Both animals show extreme site fidelity. Tom Madsen and Ric Shine have trapped the same rats over again in the one trap location or nearby.
By day both rats and water pythons lie hidden. At night both emerge in search of food ñ the rats feed on corms and the roots of sedges and grasses. The pythons are looking for a warm, furry morsel and a special adaptation helps them find it in the dark.
Pythons have unusual organs called 'labial pits'. Labial pits collect infra-red radiation and help them locate their warm blooded prey. The pits are found on the python's lips. Because there are pits on both sides of the python's head, the python can use them to orient itself for a strike. The pits can help tell the angle of the heat source in relation to the pits and the direction in which it's moving.
Like snakes, pythons also use their tongue, rapidly flicking it in and out to collect scent particles from the air and the ground. These are transferred through the roof of the mouth to Jacobson's organs which are lined with olfactory cells. Because the tongue is forked and the Jacobson's organs are paired, it's possible for the python to work out which direction the scent is coming from.
The chase. It's called a migration but it's more like a relocation.
Around December, when the rains start to fill up the homely cracks and crevices on the floodplains, the rats are forced to move house en masse to higher ground. Behind them, thousands of water pythons follow.
As the water rises, the rats crowd onto the levee banks of the rivers and into nearby woodland. Hungry pythons can travel up to 12 km in pursuit. Often they move to deep pools of water, usually not more than about 20 metres from higher dry ground, where the rats have dug in.
For the relatively long-lived pythons its a predictable but not a reliable feast. Fortunately, being cold blooded has its advantages.
A python need only eat 1/10 as much as a warm blooded animal and can go for a long time without eating anything at all.
This suits the conditions in Northern Australia very well as the number of dusky rats fluctuates dramatically from year to year. If it's a bad year for rats, the cold blooded python can simply wait through the bad times until food is available again.
Rats rely on rain. Rats numbers can vary wildly, at least 7 fold, from year to year. Just why has been something of a puzzle. It was once thought that they just drowned, but now we know that the fluctuations are caused by changes in the pattern of the wet season.
Both the timing and the amounts of rain are critical because dusky rats depend on the floodplain's deep moist cracks to provide a humid environment for their young. In the cracks the temperature stays low and fairly constant, at about 25 degrees Centigrade. Up above shaded air temperatures on the ground can vary from 20 to 35 degrees. Dusky rats show severe heat stress and die at temperatures above 35 degrees.
A heavy wet season can decrease rat numbers because soil cracks aren't formed until later in the season, so there's less time for the rats to breed. If it's a short wet season the cracks dry out too quickly resulting in less food and a shorter breeding season. A medium wet season is best. The moist soil cracks last for several months and the rats can therefore breed during most of the dry season, for as long as 9 months, resulting in a rapid increase in numbers.
Rat numbers can actually be predicted from rainfall pattern during the preceding wet season, but python numbers don't vary greatly.
Young pythons rely on young rats. Unlike snakes many pythons brood their eggs, coiling around them and often staying until they hatch. Python eggs are large and are fussy about temperature. To keep the eggs warm at some nest sites, female pythons will bask in the sun for about an hour then return to the eggs and coil around them. If the eggs are becoming too cold the python warms them by shivering ñ also known as thermogenesis. Shivering can increase temperature by up to 10 degrees.
Hatchling water pythons emerge in November and early December. The time they hatch is probably the main factor influencing the pythons' survival. If they hatch too late in the year the hatchlings will likely die and the reason has to do with the breeding habits of the rats. Newly hatched water pythons have to deal with gape-limitation. They're not big enough to swallow adult rats and need juvenile rats for their first few meals. Dusky rats grow so fast they it doesn't take long for them to become too large for the hatchling pythons. it's only during or shortly after the rat breeding season that there's the right sized food for the hatchlings.
1992 was a fairly dry year. Tom Madsen & Ric Shine were up in Kakadu checking out the rat and python action on the floodplain. In this year, rat reproduction stopped in August, 3 months before the pythons hatched. Although the rats were abundant they were too big for the pythons to eat and the baby pythons starved to death.
Female pythons reproduce about every 2 years, sometimes at high costs to themselves. The decision to reproduce is influenced by the number of rats available. In a good year only females in good condition (heavier from eating more rats) will reproduce. However in a bad year even female pythons in poor condition will reproduce. This is hard on the females. Some of them stop feeding for about 3 months during breeding and they lose up to 50% of their body mass. Many become very emaciated and quite a few will die.
Water pythons don't dig their own burrows. They rely on existing holes. In the Adelaide River study area the pythons use two quite different nesting sites. Some choose hollows in the huge root systems of paperbark trees near the edge of the floodplain. Some choose burrows dug by large goannas, Varanus panoptes, on higher drier ridges.
Each site has its own advantages. The goanna burrows are warmer and the pythons' eggs hatch up to 3 weeks earlier than those in clutches of the paperbark females. However the eggs are more likely to be eaten by predators because the female pythons leave just a few days after laying.
Only at the paperbark nests do the females stay to guard and brood their eggs. More of the eggs survive to hatching stage, but their mothers are in poorer condition and sometimes the pythons hatch too late and miss the juvenile rats.
And it was all a secret... This amazing rat and python migration has been one of Australia's best kept secrets. Both the python and the rat are only seen at night, and for many years only the local aboriginal people knew they were there, but take a walk on the floodplains at night and you might be suprised...
The Rat
Name: The dusky rat, Rattus colletti
Profile: Rats are known for their fast breeding, and the dusky is one of the very fastest. They can have up to 12 young at a time. The female is able to produce her first litter when she's only 7 weeks old and then another litter every 3 weeks after that. If all the offspring were to survive an original pair could have 400 descendants within 26 weeks.
The 6-20 cm dusky rat is a native rodent (as opposed to a marsupial rat), and has the most restricted distribution of the seven native rodents in Australia, living only in the monsoonal sub-coastal plains of the Northern Territory.
The Python
Name: The water python, Liasis fuscus,
Profile: Pythons aren't snakes, but they both share a common ancestor. Water Pythons are one of 13 species of python in Australia, and are common across the northern part of the country, found in the Kimberley, Northern Territory and tropical parts of Queensland north of Rockhampton. They're greenish with a yellowish belly and, depending on the light, they can be quite iridescent. Females grow to an impressive 3 metres, while the males max out at 2.5 metres. They're long living - mostly about 10 years, but at times up to 25 years. While not venomous they can give a mean bite.
Pythons are famous for being able to eat large whole prey. It's all in the jaws. Unlike a human jaw the python's upper jaw is not fused to the skull. It's only attached by tendons, ligaments and muscles. Also, the python's jaw is hinged back behind the cranium so that the lower jaw hinges with the upper jaw rather than with the cranium. The jaw bones are only loosely joined and the bottom jaw has another hinge about half way along. Pythons spread their bones apart and their prey slides in. Python teeth are sharp and backward curving - once inside, nothing's going to get back out.
The Rainbow Serpent
The water python is strongly connected to powerful rainbow serpent stories in local indigenous cultures. The rainbow serpent symbolises reproduction and regeneration. It has life-giving power that sends conception spirits to all the waterholes. Rainbow Snakes still have offspring. In Arnhem Land one of them is manjdjurdurrk, the water python, which because of its shining skin is the being's shadow or spirit. After the first storms the Rainbow Snakes let some manjdjurdurrk out of the waterholes and keep the rest. The snakes that are released are not Dreaming, they are maih, food which the people can eat.
In the Gunwinjgu language water pythons are called mulbu.
Pythons join the Rat Race

in this article, the reporter stated in two different places that pythons aren't snakes. The first statement was by implication in the middle of the article: "Like snakes, pythons also use their tongue, rapidly flicking it in and out to collect scent particles from the air and the ground. "

and then almost at the end: "Name: The water python, Liasis fuscus,
Profile: Pythons aren't snakes, but they both share a common ancestor."

So if pythons aren't snakes, then what the heck are they? Or is it only in Australia that pythons aren't snakes? Is that why the borders are closed to export and import of reptiles? Is it because they have these totally strange pythons that are of a different family or genus or whatever?

Something to think about on a quiet Sunday morning.
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phflame

...but I wasn't aware that tigers lived on the plains of Africa, lol.
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Chance Duncan
2.2 Retics (1.0 Tiger Het, 1.0 Lavender, 0.1 Dark Lavender, 0.1 Normal Het)
1.1 Olive Pythons
1.1 Ball Pythons (Het Albino)
http://www.rivervalleysnakes.com