Answer:
50%
Explanation:
    Z     O
z   Zz     zo
z   Zz     zo
The males will have two copies of the alleles of the genes present on the Z chromosomes. As females have only one Z chromosome, they will have only one allele for the genes present on the Z chromosome.
The results from the punnet square show that there will be chance that the females of the F2 progeny will have curved-beaks.