1. Marler, P. R., and Hamilton, III, W. J., Mechanisms of Animal Behavior, 453 (Wiley, New York, 1966).
2. Ficken, M. S., and Ficken, R. W., The Living Bird, 1, 103 (1962).
3. Marler, P. R., in Animal Sounds and Communication (edit. by Lanyon, W. E., and Tavolga, W. N.), 384 (Amer. Inst. Biol. Sci., Washington, 1960).
4. Borror, D. J., Auk, 73, 211 (1956).