[james-bcn]

I've not come across this before ("males have ZZ and females have ZW - and females have been measured to have greater variability in birds"). Do you have some references/books you can recommend? I'd like to find out more.

[SamReidHughes]

For example there is this paper on repeated differences in variance for different sexes in different groupings:

https://onlinelibrary.wiley.com/doi/10.1111/evo.12224