PARENTAL CARE AND NEST-MAKING 293 



often show stubbornness in giving up the nest, and the male 

 may have to force the female off. At other times the sitting 

 bird utters the nest-call as a call for relief, and this is some- 

 times, but not always, responded to with promptitude. The 

 same call is almost invariably given upon taking the nest, 

 but it is also uttered at frequent intervals and without 

 apparent purpose during the sitting. Normally there is no 

 courting or sexual activity during the incubation, but the 

 male often tries " to break up the cycle." 



For a week after the hatching of the eggs the parent 

 birds continue to brood. " At the end of the week the young 

 can be left uncovered for some time without harm, and the 

 period of * close sitting ' characteristic of the incubation 

 period ceases. At the end of the second week the young 

 begin to venture from the nest and become more and more 

 independent of parental care." 



The nestlings are first fed on the " pigeon's milk " — the 

 cellular debris regurgitated from the crop of both parents. 

 After the food-canal has been educated on this very digest- 

 ible material, the young birds receive the partially digested 

 food of the parents. The regurgitation-period lasts for two 

 weeks, and then the young birds, leaving the nest, pick up 

 food for themselves. 



In many birds living in natural conditions there is only 

 one brood in the season, but if a disaster occurs to the first 

 brood the reproductive cycle may immediately recommence. 

 In some birds, two broods are normal, and this is common 

 among domesticated and semi-domesticated pigeons. There 

 may be a renewal of the reproductive cycle at the end of the 

 second week, just as the young are venturing from the nest. 

 The female stops feeding and devotes her entire energy to 

 another brooding. " The male continues the feeding and 

 also participates in the incubation of the second set of eggs. 

 When the eggs are hatched, the male devotes his attention 

 to the new set of young, and the first set are forced to rely 

 upon themselves for their sustenance. ' Driving ' is some- 

 times necessary to accomplish this weaning of the first 

 young. If a series of cycles follow each other in immediate 



