Australian Green Tree Pythons
Australian Green Tree Pythons – About 45-38 million years ago, when Australia departed from Gondwana, the entire continent was covered in lush rainforest but as it started drifting northward towards the Asian plate, the continent became arid. Most of the rainforest was lost but because the continent was moving north, closer to the Equatorial zone, the climate stabilised the process and the rainforests in northeast survived. When Australia reached its present position, it was separated from New Guinea only by a shallow and narrow channel of water, as it is today. However, during glaciation periods the sea level dropped and a land bridge joined the two landmasses. This didn’t happen once, but 19 times during the ice ages of the last two million years. The last passage (100 000 years ago) was cut 8000 years ago when the sea level has rose again. Green pythons probably mingled with their northern cousins during those many low sea level periods but this connection was lost again the last glacial cycle.
Being obligate rainforest species, Green pythons found their way as far as the southern parts of McIlwraith Ranges on the Cape York Peninsula through a continuous rainforest corridor that stretched all the way from New Guinea. This happened during the later part of Tertiary (Pliocene) and Quaternary when the rainforest ended at McIlwraith Ranges. The areas near Princes Charlotte Bay and the Laura Basin were already dry and the rainforest dwelling species (not only GTPs) couldn’t traverse this dry habitat. This explains why there are no Green pythons in the relatively large tracks of rainforests further south. The estimated population size at Iron and McIlwraith ranges is about half a million and the density being 4-5 individuals per hectare.
Australian green tree pythons are the smallest of all the races and relatively uniform in colour and pattern, which consists of lime green dorsal side and flanks dotted with white, yellow or creamy scales along the spine, sometimes with short crossbars. Specimens showing patches of blue colour are rare and yellow is absent in adults except for the ventral scales or a few scales on the flanks in some individuals. The neonates are always yellow, never red or orange like some of the PNG juveniles. The Australian GTPs are invariably docile, both in captivity and in the wild.
The timing and duration of the ontogenic colour change in Australian green tree python is uniform, synchronized and fast completed. The onset of colour change is never before the age of 8.8 months and is always completed at the age of 11.3 months. The average time of complete change from yellow to green is 8 days. The OCC is also synchronized with change of habitat and diet. The yellow juveniles live along rainforest edges and gaps, where they feed on skinks during daytime. Once green, they move into the rainforest interior where they commence feeding on birds and small mammals. The big question is – what triggers ontogenic colour change. My own data suggest that it’s not body size, i.e. larger individuals do not change colour earlier than smaller ones.
Credit: Michael Cermak