This is a classic example of emotional projection. The hound has driven the prey up the tree and longs for it. Note the body position and the vocal behavior that is wholly concordant with the howl. This is the evolutionary antecedent to the howl as emotion is predicated on the prey/predator duality and dynamic.
The elements are the positive prey value out of reach. There is nothing tangible, no object to struggle against. The tree is an inert object of resistance.
Widening circles of emotional diffusion, just as when the Pack disperses, thus the RESISTANCE is experienced as a HUNGER in terms of a VOID.
This is yearning.