1276 



HORMONAL REGULATION OF BEHAVIOR 



days or weeks during which the courtship 

 attempts of the male end in "sexual flights" 

 during which the male chases the female 

 through the territory in a characteristically 

 zig-zag flight path, at the end of which con- 

 tact is abruptly broken off. Only after a 

 period of such flights is the female ready to 

 copulate. Tinbergen (1939b) reported that 

 the female snow bunting begins to build a 

 nest (and to copulate) after about three 

 weeks of this type of courtship stimulation 

 by the male. Captive female chaffinches 

 build nests and lay eggs more readily when 

 the}^ are stimulated by males (Marler, 

 1956). Vaugien (1948), working with serins, 

 and Polikarpova (19401, working with 

 house sparrows, found that females placed 

 in cages without males would build no nests, 

 whereas the presence of a male bird in a 

 cage stimulated the females to build. Male 

 and female herring gulls both build, but the 

 female seems to become stimulated to take 

 a greater part in nest-building by the ac- 

 tivities of the male, who is more active at 

 the beginning (Paludan, 1951). 



Lehrman (19o8a) reported that, when a 

 jiair of ring doves which have had previous 

 breeding experience are placed together in 

 a breeding cage with an empty nest bowl 

 and a supply of nesting material, nest-build- 

 ing occurs after a 1- to 3-day period of 

 courtship. If a male and female are kept 

 for several days in a cage containing no 

 nest bowl and no nesting material, they will 

 be ready to start building a nest immedi- 

 ately after the subsequent introduction of 

 nesting material into the cage. If both birds 

 have been pretreated with estrogen before 

 being introduced into the cage (see above), 

 the nest-building starts immediately, rather 

 than after a preliminary period of courtship 

 (Lehrman, 1958b). This suggests that par- 

 ticipation in courtship may have brought 

 the birds into nest-building condition be- 

 cause it stimulates the secretion of estrogen. 

 This is confirmed by Lehrman, Brody and 

 Wortis (1961), who found that the oviduct 

 of the female ringdove increases in weight 

 about 5-fold, solely as the result of associa- 

 tion with a male for 7 days. Significant in- 

 creases in oviduct weight can be seen after 

 less than 48 hours of stimulation by the 

 courting male. 



Warren and Hinde (1960) found that 

 the presence of the male domestic canary 

 speeds up the development of nest-building 

 behavior in the female in spring, when nest- 

 building is presumably induced by endoge- 

 nous estrogen. On the other hand, the 

 l)resence of males has no effect upon nest- 

 building behavior induced by estrogen in- 

 jection in the winter. This undoubtedly 

 means that the stimulation of nest-building 

 behavior by the presence of the male is, at 

 least in part, by way of the stimulation of 

 estrogen secretion. 



Lack (1956b) noted that the male and 

 female members of a pair of swifts (which 

 keep the same mates year after year) may 

 arrive at the nesting place on different days, 

 but that nest-building does not start until 

 the second member of the pair arrives from 

 the south, even though the two members of 

 the pair collect and use the material inde- 

 pendently of each other. Many field ob- 

 servers have noted that the songs and pos- 

 tures of male birds may stimulate 

 nest-building behavior on the part of the fe- 

 male, but it is not always certain in these 

 cases whether what is at issue is the stimula- 

 tion of a hormonal change by the behavior of 

 the male, or the stimulation of a behavioral 

 response of which the female is capable as 

 a result of hormonal changes which have 

 already taken place. There is no doubt that 

 both of these effects occur (Blanchard, 

 1941; Armstrong, 1955). 



Other external factors, such as the occur- 

 rence of rainy seasons for tropical birds 

 (Bullough 1951), the presence of suitable 

 nesting sites (Lack, 1933; Marler, 1956), 

 etc., seem to stimulate the onset of nest- 

 building behavior. 



B. EGG-LAYING 



1. Egg-laying Behavior in Birds 



The typical egg-laying pattern of the 

 domestic hen, in which eggs are laid on 

 several consecutive days, there is a gap of 

 one or more days, and egg-laying is then 

 resumed, and in which such clutches occur 

 repeatedly during much of the year, is by 

 no means typical of the egg-laying behavior 

 of most species of birds. In fact, there oc- 

 curs among wild birds just as great a vari- 



