It's not too shocking actually... it's only shocking because we
are city dwellers and don't really get to see much of these
actions.
Dogs are predators by nature, and they are well equipped to kill.
They are also territorial and hence will had an instinct to be
hostile to anything that it deems to be infringing on it's turf. In
this case the dog might not have intended to eat the kitten at all,
but was simply a rather antisocial individual with little tolerance
for any other critter crossing its area.
There are some reasons for this kind of behaviour, larger predators
have long been known to kill smaller ones to remove competition
from the food chain. Lions have a long standing habit of killing
smaller predators (Heynas, Cheetahs) and even each other at times.
Wolves often go out of their way to kill Coyotes, even taking the
effort to engage in very long chases. Dog have been known to maul
and kill smaller dogs of their own kind.
While we can train a dog to be nice by taming it, we must know that
if left to its own devices most dogs might end up being hostile to
any smaller animal that it views as killable. After all we bred
dogs from wolfs, and in every dog there is still a wolf waiting to
come out.
But hey, if you do tame a dog enough, they actually make pretty
good friends with cats. Some owners have both animals and they are
said to get along quite well.
