The sexes of non-ratite birds can be determined routinely by PCR amplification of the CHD-Z and CHD-W genes.
CHD -based molecular sexing of four species of auklets revealed the presence of a polymorphism in the Z chromosome. No deviation from a 1:1 sex ratio was observed among the chicks, though the analyses were of limited power. Polymorphism in the CHD-Z
gene has not been reported previously in any bird, but if undetected it could lead to the incorrect assignment of sex. We discuss the potential difficulties caused by a
polymorphism such as that identified in auklets and the merits of alternative CHD -based sexing protocols and primers