Given that the Terran mammalian norming for 1:1 is based upon the XX/XY chromosome pair, but that several other orders in the terran sphere are not (reptilia, piscea, to name but two)... Crocodilians, for example, determine gender by incubation temperatures.
Given that canon provides that Aslan have more dueling amongst males than amongst females (although both genders duel within gender), the 1:3 is probably not the birth ratio, which is probably closer to 1:2 or 2:5...
When the issue came up IMTG, I decided that birth ratio was 1:2, and that that was selected for by male hormone levels from the first fertilized embryo causing the other embryos to feminize, and gender fixation occuring by week 7.
Given that canon provides that Aslan have more dueling amongst males than amongst females (although both genders duel within gender), the 1:3 is probably not the birth ratio, which is probably closer to 1:2 or 2:5...
When the issue came up IMTG, I decided that birth ratio was 1:2, and that that was selected for by male hormone levels from the first fertilized embryo causing the other embryos to feminize, and gender fixation occuring by week 7.