There may be another answer to this question (as some questions do tend to have more than one answer) but I have heard it said that the reason for polymorphism can be that the resulting offspring may gravitate towards different microhabitats. Presumably to avoid competition??

I think the example that I read was referring to eyelash vipers. The more brightly colored babies were more likely to take up residence in an orchid or bromeliad whereas the duller ones were more commonly found amongst greener foliage.

Whether or not this applies to Candoia I cannot say as I'm not familiar with thier natural history.

Bryan
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"Nothing happens in contradiction to nature, only to what we know of it."