As far as I know I have never heard anything about frontline and infertility . . . I work at a vet and I know it is safe to use on preg/lactating females even tho they tell you not to on the label
and I am not sure about use in any kind of avians . . . . i don't even know if I have seen a bird in the vet with fleas . . . mites sure but then we usually treat with topical drops of ivermectin but idk that I have ever seen fleas on a bird . . . .