The "lutino" gene is a natural mutation occurring in peach-faced lovebirds. Although more common strains of peach-faced lovebirds display sexual dimorphism, or clear external differences between sexes, lutino lovebirds can be far more difficult to sex. Several indicators can help a breeder or owner to identify the sex of a pet lutino lovebird. In some situations, it may be necessary to obtain a DNA test from a veterinarian to conclusively determine the bird's gender.
Observe the pedigree of the lovebird in your care. The lutino gene is sex-linked, so it is possible to determine the bird's sex based on its parents' markings. If the father was lutino but the mother was not, any lutino offspring would be female. If both parents had lutino markings, their male and female offspring would both be lutino.
Examine the lovebird's overall broadness. This is easiest to do if you have an already-sexed lovebird to use as a basis for comparison. In general, a female lutino lovebird will have a broader head and broader shoulders than a male.
Restrain the bird so that it is lying with its back against the palm of your hand, using your fingers to hold it still. The bird's pelvis and belly should be exposed so that you can place your fingers against it. This will enable you to measure the relative width of its pelvic bone.
Palpate the bird's pelvis to find the two bony points just above the base of the tail. If the two points are close together forming a narrow point, the bird is probably a male. If you can fit your pinky between the two points, it is probably female. As a general rule, females have broader pelvic bones.
Bring the lutino lovebird to a veterinarian who specialises in the bird care. If the veterinarian isn't able to definitively identify the sex of the lutino lovebird based on external characteristics, he can order a simple blood test. This test will determine the bird's sex based on its DNA.