Dawn and dusk singing of male American Robins in relation to female behavior

It has been assumed that females are particularly fertile during the first hour after laying when the next egg to be laid is fertilized. In many passerine birds, egg laying occurs early in the morning. Hence, it may be particularly important for males to sing at dawn to attract the 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 activity at dawn but sang little around noon. Hence, the idea that mated males sing primarily to deter other males just before the 'fertilization window' was not supported. Male song activity tended to increase when the mate visited the nest during the day but less so when she entered the nest to roost at night. Synchronous emergence of all females at dawn resulted in synchronous termination of the dawn chorus, whereas a more asynchronous pattern of nest visits by females during the day and in the evening resulted in asynchronous and scattered periods of song.