National Geographic : 1988 Jan
ON THE PITILESS SIDE of evolution the fittest survive by going to extremes. Water is at a premium on Espa fiola, a parched island that has its own species of mockingbird with a sickle-like bill. These extremely aggressive characters don't miss a trick. They pestered us so much that Dieter finally declared himself chairman of the local anti-mockingbird committee. A vicious trio of them makes a fatal attack on a young masked booby (above) to drink its blood. Such situations often begin when an adult booby, unable to find a female, attempts to mate with a chick instead. The adult grabs the young bird's neck in its powerful bill, inflicting cuts. The mockingbirds go straight for the wounds. It was difficult for us to watch; we had to turn away. Friedemann Koster, former director of the Darwin station and partner in the films we made for Survival Anglia, Ltd., documented an amazing bird, the sharp-beaked ground finch. It has found only a slightly less aggressive means of obtaining liquid on a lonely, barren volcanic rock called Wolf Island. Riding on the tail of a masked booby (left), a finch pecks at the base of its host's feathers, breaking quills and drawing blood, which the finch sips as if through a straw. The finch may have learned the tech nique as an outgrowth of feed ing on flies and lice that parasitize the boobies. The seabirds pay their tor mentors surprisingly little heed, occasionally shaking their wings or taking flight to dislodge them. One in a group of 13 spe cies of birds sometimes called Darwin's finches, this bird occurs throughout much of the archipelago. But only on Wolf and a small island nearby has this extraordinary behavior been observed, earning these birds the sanguine sobriquet of "vampire finches."