PARENTAL BEHAVIOR 



1279 



day i^^ the most important factor which en- 

 sures that the reproductive system will be 

 active in the spring. In addition, experi- 

 mental work with domesticated birds indi- 

 cates that the timing of ovulation and ovi- 

 position during the day are influenced by 

 the day-night light cycle (Farner, 1955; see 

 chapter by van Tienhoven). In addition, 

 there is considerable evidence that other 

 environmental variables, such as those re- 

 lated to temperature, food supply, and so 

 on, play a significant role as regulators of 

 the breeding season (Thomson, 1950; Mar- 

 shall, 1959). 



(b) Stimuli provided by the courting 

 male apparently influence the secretion of 

 gonadotrophic hormones by female birds. It 

 will be recalled that, in our discussion of 

 the hormonal basis of nest-building behav- 

 ior, we pointed out that nest-building be- 

 havior is sometimes induced in the female 

 as a result of stimulation by the courting 

 male, and that there is reason to believe 

 that the basis for this effect is that the 

 courtship of the male stimulates the secre- 

 tion of estrogenic hormones in the female. 

 We may now examine some further evi- 

 dence of the effect of stimuli provided by 

 the mate upon the growth and ovulation of 

 the egg. Bartelmez (1912) noted that the 

 ovary of an unmated female domestic pi- 

 geon contains follicles which do not exceed 

 5.5 mm. in diameter. When such a pigeon is 

 lilaced with a male, she lays an egg after 

 about 8 days (Harper, 1904). The growth 

 of the ovum to the ovulation size of about 

 20 mm. is clearly caused by stimuli pro- 

 vided by the male. Craig (1911, 1913) kept 

 several pairs of doves so that the males and 

 females could see each other from adjoining 

 cages. The males were allowed in the cages 

 of the females daily, but were prevented 

 from copulating by the experimenter, who 

 separatefl them with a wand at appropriate 

 times. All of these females laid eggs within 

 9 days of the beginning of contact with the 

 male, although, when these birds w^ere kept 

 in isolation for a year preceding the begin- 

 ning of the experiment, 5 out of the 6 fe- 

 males had laid no eggs at all. Matthews 

 (19391 showed that the short period of tac- 

 tual contact between male and female which 

 Craig had allowed was not necessary for the 



stimulation of ovulation. He showed that a 

 female domestic pigeon would lay eggs as a 

 result of seeing a male court her through a 

 glass plate. We have found the same result 

 in my laboratory, using ring doves. Both 

 Matthews and Harper noted that, when two 

 females are placed in a cage together, both 

 may be stimulated to lay eggs. However, 

 Collias (1950) found that ring doves in 

 heterosexual groups laid more eggs than 

 those in unisexual groups of the same size, 

 indicating that the behavior of male doves 

 is more stimulating to the secretion of gon- 

 adotrophins in females than is the pseudo- 

 male behavior which some of the female 

 doves will adopt when no males are in the 

 group. 



Polikarpova (1940) placed 50 female 

 house sparrows in cages in which they re- 

 ceived additional illumination daily, start- 

 ing in the late fall. Twenty-five of them had 

 males in the cages, the other 25 were alone. 

 After about 50 days, none of the isolated 

 females had started to build a nest, and of 

 17 such birds killed for autopsy, only 3 

 showed enlarged oviducts. On the other 

 hand, all the females with males in their 

 cages had nests, and 5 out of 8 birds ex- 

 amined had fully developed oviducts. 

 Burger (1942, 1949) kept female starlings in 

 groups of various sizes, with or without 

 males. He found that, when he provided ad- 

 ditional illumination to such females either 

 isolated or in groups, their ova were stimu- 

 lated to grow to about 3 mm. When groups 

 of males and females were caged together, 

 the ova grew rather larger (5 mm.). When a 

 single male and a single female were caged 

 together, the ova of the female grew to 

 about 10 mm. This indicates that the stimu- 

 lus for the growth of the ovum is not merely 

 the presence of a male, but probably also 

 the presence of conditions which facilitate 

 the formation of a pairing relationship nor- 

 mal for the species. When Lack ( 1940, 1941) 

 caged two pairs of robins or chaffinches in 

 one aviary, the dominant pair bred nor- 

 mally, the subordinate pair did not. In such 

 birds, the full expression of normal male 

 courtship behavior toward the female re- 

 quires that the male be the territory holder, 

 which in turn means that he must be the 

 dominant bird, or the only male, in a con- 



