How do a barn owl's hunting habits help it to survive?

A barn owl typically preys on small mammals such as field voles, common shrews, wood mice, etc. The barn owl is highly adapted to hunt these mammals and is a very effective predator.
The barn owl is capable of flying very slowly and hovering, giving itself ample time to find its prey. It has the most sensitive hearing out of all the animals tested and has asymmetrically placed ears that help it determine the exact location of its prey. 
It generally hunts at dusk and dawn and determines the location of its prey by sound only. It typically hovers over the location before pouncing on its prey. When it gets ready to strike, it starts with a head-first dive and then pulls back the head to use its outstretched talons to grab its prey. Given these physiological adaptations, the barn owl is very successful at hunting its favored prey.
During the winter season, the barn owl hunts by dropping down from a perch, thus saving the crucial energy that would have (otherwise) been used in movement and also for keeping the body warm during the cold flight. 
Thus, hunting habits and physiological adaptations (such as hearing, wings, etc.) enable the barn owl to survive by hunting successfully.
Hope this helps.