Cleary these must be truly separate species It seems likely that the large pale from Spread from the central island to the southern island in comparatively recent time After both it and the small had evolved into distinct species
If differentiated forms are to persist alongside each other as separate species two condition must be met First they must avoid interbreeding In bird this is usually taken care of by differences in appearance and in the song It is no accident that bird watchers find male bird so easy to recognize correct identification is even more important for the female bird Darwin’s finches recognize each other chiefly by the beak We have often seen a bird start to chase another from behind and quickly lose interest when a front view show that the beak is that of a species other than its own
The second requirement for the existence of two species together is that they must not compete for the same food If they tend to eat similar food The one that is better adapted to obtain that food will usually eliminate the other In those cases when two closely related species live side by side Investigation show that then have in fast evolved difference in diet Thus the beak difference among
The various Galapagos finches are not just an insular curiosity but are adapted to differences in diet and are an essential factor in their persistence together. It used to be supposed that related species of bird overlapped considerably in their feeding habits. A walk through a wood in summer may
suggest that many of the bird have similar habits. But having established the principle of food differentiation in Darwin’s finch ,