I had 11 ducklings from Holderreads, 6 females and 5 males (I thought from bill color upon arrival) but a rat killed most of them. I have five survivors and am trying to figure out the sex. I thought I had two males (the smaller ones) due to the darkening of the necks, but the bills seem a lot darker than most of the pictures I have seen. Are they male? Or did I end up with only females surviving? Thanks!