DAWN AND DUSK SINGING OF MALE AMERICAN ROBINS IN RELATION TO FEMALE BEHAVIOR

It has been assumed that females are particularly fertile during the f irst hour after laying when the next egg to be laid is fertilized. In many passerine birds, egg laying occurs early in the morning. Hence, i t may be particularly important for males to sing at dawn to attract t he mate and other females and to repel potential cuckolders. I studied song activity of mated male American Robins (Turdus migratorius). Egg laying occurred close to noon. However, males had a peak song activit y at dawn but sang little around noon. Hence, the idea that mated male s sing primarily to deter other males just before the 'fertilization w indow' was not supported. Male song activity tended to increase when t he mate visited the nest during the day but less so when she entered t he nest to roost at night. Synchronous emergence of all females at daw n resulted in synchronous termination of the dawn chorus, whereas a mo re asynchronous pattern of nest visits by females during the day and i n the evening resulted in asynchronous and scattered periods of song.