jazz710: Mrs.Sharpier: Yes yes yes very cute. But it's fascinating to me that more females are born when a species is in captivity or endangered. Do any zoologists out there care to explain this phenom?

I also recall reading that during times of war, more human babies are female too, I wonder if these reasons are linked?

There was one incredibly poor study done showing sex-ratio skewing in captive populations, but the data were REALLY poor and shouldn't be taken without a whole bag of salt. In terms of why more female babies may (or may not) be born in captivity, it's incredibly important to consider that in mammals, you should look at the sex both at conception and at birth. It's much more likely that if there is a trend of female bias in captivity, it's occurring through non-random miscarriage (animals not getting the right nutrition could lead to one sex of embryo paying a larger price than another) rather than some underlying genetic reason. In mammals, dad gives an X or a Y and we're talking about millions of sperm per event at pretty darn close to a 50:50 ratio (barring any genetic abnormality, meiotic drive, etc.).

I'd like to see the data that in captivity hippos are at a 5:1 female:male sex ratio. That seems too incredible to be real given the way that sex is determined in mammals. Zookeepers, while they're great at their job, are not statisticians and can stretch anecdotal evidence much farther than a reproductive biologist may.

/Reproductive biologist
//Don't work on mammals, they're boring,
///Turtles ftw.