Rhythmic occurrence of sexual behavior and egg laying activity of Muscovy ducks

1. The existence of nychthemeral rhythms in the sexual behaviour of Muscovy ducks, kept under intensive husbandry conditions, was investigated. Studies were also carried out of the relationships between artificial insemination or natural mating times, oviposition time and female fertility. 2. Sexual activity (as measured by the number of complete matings observed) followed a trimodal pattern with peaks of activity in the second to third, 5th to 6th and 10th to 15th hours of the photoperiod. The last peak in sexual activity was the most important in both length and intensity. 3. The rhythm in sexual activity was entrained by the light-dark transition. 4. Female fertility was lowest during the period from 4 h before to 1 h after oviposition and greatest in the periods 8 to 4 h before and 1 to 7 h after oviposition. 5. The periods of maximum female fertility did not coincide with the periods of greatest sexual activity. More than 60% of all matings observed occurred during periods of intermediate female fertility. It would therefore appear that natural mating is not consistent with optimal female reproductive performance under artificial husbandry conditions. 6. The results are discussed in relation to a possible reduction in the number of males necessary in breeder populations in Muscovy ducks with a view to reducing the cost of producing ducklings.