This research looked at how different factors influence sperm quality and quantity in pheasants and their relatives. The scientists studied how things like competition between sperm, the size of the males, and how long females store sperm affect the characteristics of sperm in these birds. They found that in species where males mate with multiple females, the volume of sperm, the number of sperm, and how healthy the sperm are seem to be higher. Additionally, the more time a female stores sperm, the more sperm the male produces, even though the individual sperm become shorter. The researchers discovered that various factors like competition and body size play roles in shaping the complex traits of bird ejaculates.