Dubbed "Big Bird" by the graduate student who noticed him, the immigrant charmed a local female medium ground finch (Geospiza fortis) and established a family of hybrids. The unusually shaped beaks of their offspring proved suited both to eating Tribulus seeds of all sizes, where many finches are restricted to eating only large or small ones, and eating cactus nectar that only some other species can reach.
Galapagos finches choose their mate in part based on beak size and shape, but apparently, most of Daphne Major's other inhabitants found nothing sexy in such diverse mouthparts. Moreover, although Big Bird's mate apparently found his offshore accent delightful, other females of her species disagreed, so the pair's descendants bred almost exclusively among themselves, rather than with members of the island's three pre-existing species.
"A naturalist who came to Daphne Major without knowing that this lineage arose very recently would have recognized this lineage as one of the four species on the island. This clearly demonstrates the value of long-running field studies," said Professor Leif Andersson of Uppsala University, Sweden. Along with the Grants, Andersson has announced the results of the sequencing of the genome of Big Bird and many of his descendants in Science, confirming it took just two generations for a new species to appear.
Daphne Major's tiny size and the Grants' outstanding attention to detail mean we have a record of the mating history of every Big Bird descendant. Nevertheless, until recently the Grants were doubtful if the birds they observed met the requirements to be considered a new species, rather than simply a variety of a pre-existing one. Yet the family is establishing its own successful niche, having grown to eight breeding pairs and 23 individuals after six generations.
The survival of the new lineage remains perilous. The population peaked at 36 in 2010 before some bad seasons reduced it. Climate change or introduced species could make Daphne Major less comfortable for finches in general, in which case the smallest population could easily be the first to die out. In the meantime, however, the Grants have a front row view of a species establishing itself, something previously only seen in butterflies, and outside the animal kingdom.