Is There a Species on Daphne?

We see the birds that have obviously originated on another island. For example, the small groundfinch. Round about july, august, september, there'll be scores of them on daphne. And then the following breed breeding season, they suddenly disappear. We were tempted to declare the discovery of a new species but then in discussion, we said, well, how many generations should they be isolated from the parental species? Are you satisfied with two? Oh, no, no, that's much too short. But about three or four? Er wel, i'm convinced that theyre er an entity that should be recognized as something separate, but i'm not so sure