Birds have sex chromosomes labelled Z and W. The chromosomal requirements for a male in birds is the opposite of that in mammals as the female is the heterogametic species rather than the male. Therefore ZZ results in a male and ZW results in a female. | Birds have sex chromosomes labelled Z and W. The chromosomal requirements for a male in birds is the opposite of that in mammals as the female is the heterogametic species rather than the male. Therefore ZZ results in a male and ZW results in a female. |