We had been watching this moose family on Slumgullion Pass near Lake City, Colorado, in the heart of the San Juan Mountains. The cow and calf had begun making their way higher up the mountain, but this magnificent bull wasn't quite ready to follow.

For a few moments, he remained behind, standing among the willows and autumn grasses as if he had something important left to say. With his head lifted and mouth open, he seemed to call into the mountain air before eventually following his family uphill.

It was one of those fleeting wildlife moments that leaves you wondering what you have just witnessed. Was he calling his cow? Announcing his presence? Simply answering the irresistible pull of the autumn rut?

Whatever the message, there was something wonderfully wild about watching this powerful bull pause beneath the golden foliage of the San Juans before disappearing up the mountain after his family.