Steve August, of Dunedin, asks :-
Iâ€™m just back from visiting family in Brisbane in November. We were walking round a lake and saw this goanna digging up a clutch of about eight eggs, and munching and swallowing them all down. This was in soil beside a walking track, only a few metres up from the side of the lake. I gather there are turtles in the lake so we thought they might be turtle eggs. However they made a definite crunch and I thought turtle eggs were leathery and more spherical. They were a uniform dirty white colour, about 25-30mm long, oval (but not peaked at one end like a henâ€™s egg), and buried in fairly loose soil about 80mm deep.
What sort of eggs do you think they were?
Arthur Georges, an ecologist at the University of Canberra, responded.
Freshwater turtles abound in our rivers, lakes, ponds and wetlands, but are often secretive, noticed only when they put their snouts above water to breathe. An exception is when they come on land to lay their eggs, which they do in nest chambers constructed in the soil with their hind limbs. Having laid the eggs, the mother turtle takes much care to conceal the nest, but predators, like the goanna, are equally skilled in finding the freshly laid eggs. This goanna (Varanus varius) is in the process of guzzling down a clutch of turtle eggs. The eggs are hard-shelled, white, and oblong in shape, with around 15 eggs, but up to 25 eggs, laid at a time. It is not possible to identify the species of turtle with any certainty, but looking at the soil and litter and its proximity to water, the nest was almost certainly laid by a Brisbane river turtle (a subspecies of Emydura macquarii), though it could also have been the eastern longnecked turtle (Chelodina longicollis). The other turtle species in the area, the broadshelled turtle (Chelodina expansa), lays its eggs in the autumn and early winter.
This is a lucky find for this goanna. Foxes too are a big predator of turtle nests, and devastatingly efficient. You have to get up early to beat the foxes to any nests. You can see the evidence of fox predation clearly, because foxes, unlike goannas, slit the egg open with a tooth, and then swallow the contents, leaving the eggshells scattered about the uncovered nests. The goanna swallows the eggs shell and all, leaving little trace when the meal is finished.
Both goannas and foxes rely heavily on scent to locate the nests, and so if they can go undetected for a few days to a week, they will probably go undetected by predators. Those that do survive the onslaught, will hatch out in mid to late summer and make their way to water where they face another suite of challenges to their survival. It is a good thing that turtles live so long, and lay so many eggs in their lifetime.
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