You can see that the heron is already gathering its neck in for takeoff. Wise move.
Cranes, by the way, fly with necks extended, and that's a quick and easy way to tell them from herons in flight. Cranes also lack a functional hallux, or hind toe, so they can't land in a tree like a heron can. They are open country birds, who can't perch but must stand on solid ground or in shallow water. This impacts their habitat preferences and natural history in lots of ways. (Thanks to Paul Tebbel for some thought-provoking conversation on cranes while we drove around in his truck).There are two species of sandhill crane at Bosque del Apache, the greater and lesser sandhill cranes. Lesser sandhills are much smaller than greaters (the bird in the middle with brown wings is a lesser sandhill). They also tend to "paint" their wings more heavily with iron oxide, so they really stand out in a crowd. Yes: cranes decorate their feathers by painting them with red-staining mud. That's why you'll only see the stain on the parts of their bodies they can reach.
Cranes on green, a lovely sight. The second bird from the left is probably a lesser sandhill crane. In the photo below, the brown-winged lesser sandhills are easy to pick out, markedly smaller than the pale greaters. How I miss their resonant calls. Cranes are addictive.