22 FORM AND HABIT: THE WING. aquatic Grebes and Ducks, protected by the nature of their haunts and habits, lose all their wing-feathers at once, and are flightless until their new plumage has grown. It might then be supposed that permanently flightless forms would be found among the Grebes and Ducks. But these birds are generally migratory, or, if resident, they usually inhabit bodies of fresh water where local conditions or droughts may so affect the food supply that change of residence would become necessary. However, on Lake Titicaca, Peru, there actually is a Grebe which has lived there long enough to have lost the use of its wings as flight-organs. Rails are such ground-lovers, and fly so little, that we should expect to find flightless forms among them when the surroundings were favorable for their development. In Kew Zealand, that island of so many flightless birds, the requirements are evidently fulfilled, and we have the flightless Wood Hens. Here, too, lives the flightless Gallinule, Notornis, and in this family of Gallinules, birds not unlike Coots, there are at least four flightless species inhabiting islands — one in the Moluccas, one in Samoa, one on Tristan d'Acunha, and one on Gough Island. The last two islands are about fifteen hundred miles from Cape Good Hope, and have evidently never been connected with a continent. There seems little reason to doubt, therefore, that the ancestors of the Gallinules now inhabiting these islands reached them by the use of their wings, and that these organs have since become too small and weak to support their owners in the air. Other cases might be cited ; for instance, the Dodo of Mauritius among Pigeons, and the Kakapo {Stringops) of New^ Zealand among Parrots ; but if the illustrations already given have not convinced you that disuse of the wings may result in loss of flight, let
