https://www.livescience.com/13681-duck-ejaculate-sperm-antibiotic-beaks-110412.html
Brighter Duck Bills Indicate 'Killer' Sperm | Live Science
Apr 12, 2011 - Mallard ducks with bright beaks (a sexually selected trait) have ejaculate with better antibiotic properties, which can help keep their mates healthy by...
killer spermbrighterduckbillsindicate