What is an 'ecological niche'?

The ecological niche describes a way of living that provides a species with adequate nutrition, an optimum environment, and as few enemies as possible. For instance, several different species of water birds can live together peacefully on the sea because each species prefers a different food or hunts for its food at different depths in the water. 

The birds do not prey on each other's food, and hence are not natural enemies. We can also say that this particular animal species has become specialized.