To get an erection, ostriches and emus lengthen their penises using lymphatic fluid , unlike mammals and reptiles, which use blood. This is what emerges from a study published in the Journal of Zoology . To demonstrate this, the researchers dissected the genital organs of an adult ostrich ( Struthio camelus ) and three emus ( Dromaius novaehollandiae ). Both have paralymphatic bodies under the muscles that control the phallus.
According to Patricia Brennan, an evolutionary biologist at the University of Massachusetts, the lymphatic erection mechanism must have arisen for the first time in a common ancestor of all birds . The reason for the change from a blood vascular system to a lymphatic one in the case of these birds is still a mystery.
Only in 3% of bird species do males have penises, including ostriches, emus, kiwis, geese, cinemas, ducks and flamingos. The rest of the birds reproduce through what is known as a "cloacal kiss," during which the male on top of the female transfers the sperm using the cloaca route, the same tube used for excretion.
