Adult male!
(I went afk and suddenly I had an adult, uh thanks anonymous peep?)
Such an amazing looking sprite, wow
EDIT: Almost forgot the adult description~
"Once their adult feathers grow in, thunderbirds are often too big to stay in their magi's rooms - much to the relief of any magi with important paperwork. They prefer high places and will often fly to the top of The Keep to roost on any outcropping large enough to support their weight. They must be kept away from snakes like the Raza cobras and vitons, as they consider these creatures their mortal enemies. An adult thunderbird is a little more mature than a hatchling, but that doesn't stop them from occasionally causing a thunderstorm just to send everyone running into shelter, and they still create complicated dances, especially just before more natural rainfall."
The hatchies are pretty cute
-flails- I got one!
+ dimorphism, I am a happy happy girl. 
