This is different from mammals, where males determine the sex.
Here's why:
* Chromosomes: Birds have a ZW sex determination system. Females have two different sex chromosomes (ZW), while males have two of the same (ZZ).
* Egg contribution: The female bird contributes a Z or a W chromosome in the egg, while the male bird always contributes a Z chromosome.
* Offspring sex:
* If the female contributes a Z chromosome, the offspring will be male (ZZ).
* If the female contributes a W chromosome, the offspring will be female (ZW).
Therefore, the sex of the offspring is determined by the chromosome contributed by the mother bird.