My life : a record of events and opinions - Wallace-online.org

382 MY LIFE3. In 1867 I gave a provisional solution of thecause of the gay, and even gaudy colours of manycaterpillars, which was asked for by Darwin, andwhich experiment soon proved to be correct. This isfully described in my " Natural Selection and TropicalNature," pp. 82-86. The principle established inthis case has been since found to be widely applicablethroughout the animal kingdom.4. In 1868 I wrote a paper on "A Theory ofBirds' Nests," the chief purport of which was to pointout and establish a connection between the colours offemale birds and the mode of nidification which hadnot been before noticed. This led to the formulationof the following law, which has been very widelyaccepted by ornithologists : When both sexes of birdsare conspicuously coloured, the nest conceals the sittingbird ; but when the male is conspicuously coloured andthe nest is open to view, the female is plainly colouredand inconspicuous. No less than fifteen whole familiesof birds and a number of the genera of other familiesbelong to the first class, of brightly coloured birdswith sexes alike, and they all build in holes or makedomed nests. Most of these are tropical, but thewoodpeckers and kingfishers are European. In thesecond class, however brilliant the male may be, ifthe nest is open to view, the female is always plainlycoloured, sometimes so much so as to be hardly recognizableas the same species. This is especially thecase in such birds as the brilliant South Americanchatterers and the Eastern pheasants and paradisebirds. This law is of especial value, as showing theexceptional need of protection of female birds as wellas butterflies, and the remarkable way in which thecolours of both classes of animals have become