Near a bird's/parrot's vent are the "ends" of the pelvic bones. It is usually/often/sometimes true that the pelvic bones of the male are closer together than the female's, since the feamle's have to allow for passage of an egg.

However, some males have widely spaced pelvic bones, and some young females' are close together and spread when they get older or lay their first egg. So, "pelvic sexing" consists merely of feeling how far apart the ends of the pelvic bones are and guessing male or female based on that information.

I have been doing this with my cockatiels for many years, and on the 20 or 25% of birds that I am pretty sure what they are, I'm about 90% correct. On the other 75 - 80% of birds, the bones are not close enough together or far enough apart for me to feel confident guessing, and if pushed I'm barely more accurate than if I just "guessed."

So-called "pelvic sexing" is NOT reliable or accurate enough to be useful, and should not be trusted. Oh, if you're just curious about your pet and somebody offers to check the bones for you and gives you an "educated" guess - no harm done. But, I wouldn't even CONSIDER trying to put pairs together or breed birds based on this! Your only real choices are surgical sexing or DNA testing.