This is Big Boy (confusing when a lion i worked with in africa had the same name) the red deer stag from a local wildlife park in Kent, Wildwood. It's early summer so he still has velvet on his antlers. In the wild the rut would begin in the autumn where red deer stags compete with each other and herd the hinds and make loud roaring calls. They rarely get to rest or eat so the summer is the last rest they get. Though in captivity big boy's calls can been heard throughout the autumn.