by maricksu moderator
David and Tillydad, would you add more info here.
Great photo of younger and older male. In classifying I would though consider also left one as adult, horns already quite long, probably already living in bachelor herd. But not absolute sure what is the best way to classify male impala (young/adult) in our photos.
I guess we have had no strict rules in our classifying, how to define young male impala (so don't worry if have chosen young, not "wrong"). Sexual maturity would be one measure but I guess, that would be very hard to connect with the looks. I’ve though simply classified those young with smaller size and short horns (straight, up-to/just exceeding ear-length, still living in maternal herd, not yet evicted by ’boss’-male to live and grow up in bachelor herd) e.g. ASG001oi17 , ASG001pt4j 😃
I think I agree with you M; in practice most people will probably call this subadult an adult, and the little guys with short spike horns will generally be considered young. Males start showing horns about 4-5 months and by 8 months most have left the natal herd. But they are not really 'socially mature' till about 4-5 years.