In act ii, scene iv, of macbeth, the audience hears reports of an owl killed by a falcon and of a horse eating another horse. what is the likely significance of these events?
they signal banquo's and malcolm's impending doom.
they highlight the disruption of the natural order caused by macbeth's crime.
they symbolize the internal conflict in macbeth.
they symbolize the conflict between macbeth and lady macbeth.

A falcon was killed by an owl, not the other way round - there is a mistake in your question. 
However, the likely significance of these events is that they highlight the disruption of the natural order caused by Macbeth's crime.
Usually, a falcon can kill an owl, and horses don't normally eat each other. But since Macbeth has killed the king, he has disturbed the order in nature and thus these strange things happen.

Say again and i will be sure to