292 THE BIOLOGY OF BIRDS 



laid ; in other cases incubation may be delayed, or may be 

 very intermittent, until the advent of the second egg. This 

 has an interesting result, that the period required for the 

 second egg is generally shorter, and " the shortening of the 

 time for the second egg secures a greater equality of the two 

 young birds in feeding." This is important because the 

 stronger and better-developed nestling is rather apt to 

 monopolise the nutritive attention of the parents. 



Most species of pigeon lay two eggs, but some lay a 

 single egg ; and species that lay two may sometimes lay only 

 one. Even when no egg is laid, the bird may persist in 

 incubation. The first egg is always dropped in the 

 afternoon ; the interval between it and the second egg is 

 variable, but it is very frequently i day, 14 hours. In many 

 cases the female pigeon shows diagnostic symptoms before 

 laying : " the wings are held loosely and allowed often to 

 drop below the tail ; the bird looks as if sick, and moves 

 about heavily and with unusual care " ; she may sit on the 

 nest for 3-4 days before laying. The young birds usually 

 hatch in the early morning or forenoon. Rarely or never 

 do they hatch in the afternoon. If the hatching has not 

 occurred by 3 p.m. one may be almost certain that nothing 

 will occur until the next morning. It seems probable that 

 the young bird, within the egg, has its times of resting, which 

 correspond with the times of resting in the parent bird. If 

 a young bird has partly cracked the shell, but has not finished 

 before noon, it may " go to sleep and wait till next morning." 

 The egg-shell is usually first pricked about 24 hours or 

 more before the young bird liberates itself, and the breakage 

 is almost invariably at the larger end. " Both parents 

 exhibit an increase of interest in the nest at hatching-time. 

 This is not necessarily due to the presence of the young, as it 

 may manifest itself before the eggs are hatched." 



Both parents share in the brooding. In the pigeons 

 studied by Whitman the female sat during the night, while 

 the male normally roosted on the perch as far from the 

 nest as possible. During the day there is alternation, but 

 the male sits for the greater part of the time. Both parents 



