Explain why ALL cormorants are or are not flightless.

These cormorants evolved on an island habitat that was free of predators. Having no enemies, taking its food primarily through diving along the food-rich shorelines, and not needing to travel to breeding grounds, the bird eventually became flightless.

Explanation:

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.