FERTILITY IN CAPTIVITY 151 



common almost all across the Old World, are really 

 more abundant than any bird which ever nested 

 in close-packed colonies and flew in cloud-like 

 flocks. 



The fertility of birds laying several eggs appears 

 to increase with age ; the Swan, for instance, lays 

 twice as many eggs when mature as she usually does 

 when starting laying in her second year. It is true 

 that domestic Hens decline in fertility in a year or 

 two ; but then they are expected to lay in one 

 year twenty times as many as their wild ancestress 

 does. Tame Ducks are more fertile ; with an 

 equally exaggerated egg-production, they lay a 

 paying amount of eggs at any rate in the case of 

 the prolific Indian Runner breed for twice as many 

 years as a hen. 



Yet the Muscovy Duck, the Turkey, and the 

 Goose have not had their fertility increased as a 

 rule above that of wild birds. These always have 

 eggs in reserve ; even if the set be only one or 

 two, others will replace it at least once in case of 

 accident, and birds which lay several eggs will 

 under artificial stimulation produce numbers at 

 times as great as an inferior domestic Hen. An 

 unfeeling naturalist once made a Wryneck lay forty 

 eggs in a season by removing them as fast as laid, 

 a piece of brutality which very probably ended in 

 sterilizing its subject, as an extreme output in one 

 year is likely to reduce subsequent prolificacy, as 

 one would expect. In a case I heard of in which a 

 hen Silver Pheasant laid seventy eggs in one season, 



