I just got to thinking...
I have read that incubation temperature regulation has often been tentatively linked to determining sex in some waterfowl species. I cannot deny that in 2012 we hatched a clutch of 8 female East Indian wandering whistling ducks, and this did strike me as more than coincidental...
I decided to look into it a little more, and, chatting with Nigel Jarrett - Head of species conservation, we discussed the following.
Birds have a ZW system of sex determination (sort of reverse to humans) and in that system sex is determined by the female within her ova, and the sex of offspring is not affected at all by the sperm which the male contributes. When the egg leaves the ovary and meets the sperm before passing into the oviduct, the egg is already containing the chromosome that determines the sex. Incubating the egg in a certain way should not affect the sex at all.
It cannot be said that certain females mightn't be susceptible to external factors such as temperature and stress which might help pre-determine which chromosome of eggs she randomly creates. For example, I have a really butch angry female Nene, (BAP above) which always seems to lay male eggs. I wonder whether she has unnaturally high testosterone levels, for example?
It feels as if I have always known this, but it has never stopped me wishing that I could somehow manipulate things for my benefit... This season I plan to keep ratio updates for my specific pairs in my diary, and over time, look into it. If anyone has actually studied anything on sex determination and would like to comment below; please do educate me!
In the mean time, the first step might be to see what BAP throws me in the way of boys from her nest of 2013 above!
