The proposed generalizations or "principles" are as follows: 1. Class limitation, as determined by structure. 2. Species limitation, or exclusive specialization: the impossibility that a species should excel in all the capacities of its class. 3. Minimum versatility, or the monotony threshold: mutual exclusiveness of repetitiveness and continuity. 4. Maximal continuity, or (in combination with the receding) the positive correlation of continuity and versatility. 5. Spatial detachment of continuous singing from feeding. 6. Correlation between quantity and quality: better singers produce more song. 7. Unequal distribution of musical ability by families. 8. Relatively equal geographical distribution. 9. Ecological distribution according to: invisibility; sexual monomorphism; territoriality; number of Oscinine species in the area; scarcity of strong-voiced, primitive species, sound-transmitting characteristics of the habitat; efficiency of feeding methods; mild weather. 10. Sex distribution according to climate (female singing intergral to the life-pattern of a good many species not subjected to cold weather or migration). 11. Innately-guided imitation and learning. 12. Possible light-dark influence upon exuberance in song.