When visiting Hawaii on vacation, a tourist notices that there are many different species of birds that look similar to one another, but are distinct in their ecology and in the morphology (beak size and shape) that helps make them successful in different habitats on the island. The tourist supposes they are closely related and result from an adaptive radiation. Which of the following statements would provide the STRONGEST evidence they are the result of an adaptive radiation?

Some, but not all of the species can hybridize.
The species move throughout all areas of the island.
Variation in beak length within any of the species is distributed like a bell curve.
The phylogeny of the birds shows a single common ancestor for the group.