was there not something years ago about the temperature of incubation...It was probably an old wives tail, but it was something to do with a temperature difference, supposedly it was to do with evolutionary mechanism whereby you need more females to males in order to keep population high so the eggs in the middle of the clutch which are very slightly higher would be more likely to be male whereas as the majority of eggs are on the outside they would be cooler and therefore more females...I know this is probably a load of nonesense but maybe someone out there has some information on this