It’s because it depends on habitat and also on how many males and females are in pen. I had my mine a male for about 6 months by himself the I put 4 females with him. Moved him to a bigger pen and after 2 years then incubated eggs and had 6 added after 3 months old. But I didn’t realize that they were to many males.. so after a year more almost 4 yrs the other cotunmix males started killing each other and hurt the females and so they died off. Have one left. Just bought him a female will keep an eye out to see what happens. Was told add more females.I have been searching everywhere, but I can't find an answer which everyone agrees on. Some say 2 years others say 7. I'm talking about Coturnix in captivity by the way, lol. Thank you for any answers