similar transformation ).
The evolutionary significance of this mechanism is poorly understood , and the big question that remains is : why is it important for GTPs to have yellow or red babies ? Wilson et al . ( 2006 ) suggested that the yellow juveniles live mainly along the rainforest edges , where they rest and hunt just above ground level for skinks and invertebrates whilst remaining less visible against the leaf litter and Guinea Grass from above . It has since been established that the juveniles also feed on small frogs , and although they may snap at insects passing by , bugs are certainly not part of their diet . In fact , no species of python is known to feed on invertebrates .
Upon changing to green in colour , the young pythons move into the rainforest canopy where they are now effectively camouflaged , and they also switch prey items from skinks and frogs to small mammals and birds . Wilson and his colleagues used the von Bertalanffy growth model to estimate the age of juveniles and suggested that OCC takes place between 0.9 and 1.1 years of age . They concluded that OCC appears to be size mediated , with snakes changing within a very limited size range .
I have been collecting data on OCC from captive Green Pythons since 2007 . During this time I have amassed a large body of information from more than 60 individual snakes - a significantly larger number than were available to Wilson et al . Opinion was divided amongst my colleagues as to the trigger for OCC in Green Tree Python juveniles , so I
‘ Why is it important for GTPs to have yellow or red babies ?’
decided to test whether there was a correlation with age and / or size . Because snakes are notoriously difficult to measure accurately , I chose to use body weight rather than SVL to quantify size . I also recorded the exact number of days that it took each snake to change colour .
Importantly , my findings differ considerably from those of Wilson ’ s study . Body weight at OCC ranged from 60-110 grams because the snakes grew at different rates , despite being subjected to the same feeding regime . However the timing was pretty constant ; clutches were all hatched about the same time and all animals changed colour within a two week period . This indicates that OCC is independent of weight but is temporally triggered .
The twins I hatched in 2008 are a good example . They were 5.6 and 6.5 grams respectively at birth , which is about half the body weight of a normal neonate . Nevertheless , they changed colour shortly after their siblings , which were still much bigger at the time . The twins weighed 16 and 26 grams at OCC , whilst their siblings had attained a body weight of 40-62 grams .
We should also consider non-native races of the species . From my limited experience and information received from other GTP breeders , many of the non-Australian juveniles start changing colour at a very early age ( as little as three months ) and this process can last several months , or even years before it ’ s completed . Because we don ’ t have reliable information about the true origins of these non-natives , it ’ s hard to say whether there are regional differences in the OCC . However , the OCC in Australian populations is temporarily well-defined and synchronized compared to nonnatives , and the duration of the