A frigatebird depends on the sea for its sustenance. But it cannot dive into or land on the water. It must snatch food with its long hooked bill from near the surface, or chase other birds to steal a meal. Kleptoparasitism is the term for that. In order to accomplish these feats, it must be able to maneuver deftly through the air. Narrow pointed wings and a long forked tail permit and facilitate this.
A sea lion is very much at home in the water, but has some difficulty on land. It uses both for different purposes, but the sea is where it secures its food. Therefore it is an efficient and powerful swimmer. What it lacks in grace on land is made up for in the liquid medium.
Every life form has different needs for survival. There are generalists and specialists, each with advantages and disadvantages. One technique is to have a lifestyle that is different than anything else, where competition is minimized. Success depends on many factors; harmony with the environment is a crucial necessity.
