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Re: Turtle nest gases ref.




On Fri, 12 Mar 1999, Dann Pigdon wrote:
> The Madagascan elephant bird seems to have buried its eggs in sand
> dunes, perhaps because it was too heavy to incubate them directly.

I could offer two hypotheses for this.
1.  Birds try to maximize rates of incubation.  Comparisons of NZ and
Australian incubation times for comparable species show a more leisurely
rate on NZ.  This is probably due to a more benign predator regime in NZ.
Perhaps, due to absence of felids and canids on Madagascar, elephant birds
could even afford to lay and leave like turtles _and_ some megapode birds
which incubate in volcanic soils do.  Indeed, it may be that in following
the strategy of laying in a dry environment (also employed by ostrich and
emu) it had _no_ predators at all on its eggs and hatchlings!  In that
case food may have been limiting, i.e., forage time was more valuable than
time spent with egg.
2. It may have incubated _through_ the sand like the Egyptian plover.

> However
> some megapodes seem to be able to utilise forest soils. Perhaps the
> careful regulatory behaviour of megapodes compensates for this,
> whereas turtles just lay and leave. 

They use a mixture of leaves and soil and the heat of decay to incubate
their eggs (like some alligators and dinosaurs).  But, yes, parental
attendance is necessary--the eggs would suffocate were it not for the
aerating efforts of the parents.

> Perhaps if dinosaurs
> also tended buried or partially buried eggs then the soil composition
> may not have been so crucial.

Right.  To lay eggs in the forest they would have had to attend them.

> It would be interesting to compare the soil types associated with oth
> theropod and sauropod eggs. I can envisange theropods regulating
> the incubation environment of buried eggs, but somehow sauropods
> just don't seem to have been the most delicate of creatures (at least
> direct incubation via brooding is probably out of the question).

Yes.