My friend has a mated pair of Swainson's Lorikeets (Trichoglossus haematodus moluccanus), a subspecies of the Rainbow Lorikeet, that he hopes to breed.
The female is 3 years old, and has just laid her second clutch of eggs since my friend got her. The male is 15 years old and is a proven sire, though with a different, now deceased, female. The birds have sex frequently but the first clutch of eggs were clear, so he's concerned that the male may no longer be fertile. These birds can live to their late 20's, so 15 seems a little young to stop producing sperm. A bird specialist vet examined them recently and said they were both in good health; my friend didn't have any fertility tests done at the time (he says he will if this clutch also turns out to be clear).
Given all of the above, until what age will a male Swainson's Lorikeet typically remain fertile?