Other perfectly natural animal actions include "stepfathers" killing the young of another male to make room for their own offspring, stressed mothers eating their own young (usually alive, and usually starting from the tail end), fathers eating their own young, and casual cannibalism. They also include the stronger offspring killing the weaker, and adopted young killing the natural born offspring.
If we accept that "natural" is an argument to approve of immoral actions, where does the line get drawn?