REPRODUCTIVE ENDOCRINOLOGY IN BIRDS 



1143 



group. Barry (1960) found a correlation be- 

 tween snow cover and the date of first egg, 

 whereas the correlation between date of first 

 egg and clutch size was 0.79 to 0.85. From 

 his data it appears that the ovaries are in the 

 beginning stages of development when the 

 birds arrive at their breeding grounds in the 

 arctic and that full ovarian development oc- 

 curs during the prenesting interval. Ovula- 

 tion seems to be dependent on the availabil- 

 ity of nesting sites, although lack of food 

 was not completely excluded as a factor. A 

 sharp decrease in average clutch size takes 

 place when the interval between arrival on 

 the breeding grounds and laying of the first 

 egg exceeds 7 to 10 days. 



Barry (1960» counted the number of 

 atretic and ruptured follicles and compared 

 these with the average clutch sizes. In this 

 manner he could show that each egg not laid 

 because of unfavorable conditions was rep- 

 resented by an atretic follicle. 



For the males of these species the situa- 

 tion seems somewhat different. Testicular 

 weights decrease and lipoidal infiltration of 

 the tubules starts, apparently immediately 

 after the males arrive at the breeding 

 grounds. Corroborating evidence for the hy- 

 pothesis that spermatogenesis may already 

 be past its peak on arrival at the breeding 

 grounds is found in the fact that neither 

 Barry (1960) nor the Eskimos in this area 

 have ever seen brant or snow geese copu- 

 late. Also, sperm were found in the oviduct 

 of a brant killed on arrival at the breeding 

 grounds. It was not possible to establish 

 whether the rate of testicular collapse would 

 proceed at different rates in the presence or 

 absence of nesting sites and plentiful food. 

 Marshall and Roberts (1959) studied the 

 fish-eating cormorants, Phalacrocora.v carba 

 and P. afncanus, which breed in the 

 northern Lake Victoria region. These species 

 apjiarently can breed the year around, but 

 within the species different segments of the 

 jioi^ulation are in different phases of the 

 reproductive cycle, so that no pair breeds 

 twice without a pause long enough for an- 

 other pair to breed at the nest they have 

 just abandoned. It seems from the observa- 

 tions that the availability of nests and nest- 

 ing sites determines the breeding behavior 

 for each segment of the population. 



Vaugien (1948), with very few birds, 

 showed that canaries would not lay when 

 the female was deprived of cotton to line 

 the nest bowl. The condition of the ovary 

 was not mentioned. However, when the nest 

 bowl was warmed by an electric coil, ovipo- 

 sitions occurred in the absence of the cotton 

 lining. Unfortunately, no information con- 

 cerning the ovaries was published and so 

 few birds were used that any inter])retation 

 is very tentative. 



8. Psychic Factors 



A variety of psychic factors have been 

 shown to affect the breeding of birds. Craig 

 ( 1913) noticed that a dove which had failed 

 to lay started to do so 9 days after Craig 

 started to stroke her daily. Matthews (1939) 

 later established that an isolated female 

 pigeon could be stimulated to lay a normal 

 clutch by the sight of another pigeon or even 

 the sight of herself in the mirror. Vaugien 

 (1948) noted that the canary needs a part- 

 ner, male or female, in order to lay. House 

 sparrows, in which the male and female are 

 dimorphic, are apparently more discriminat- 

 ing than pigeons, in which male and female 

 look alike. Female sparrows will not show 

 any oviduct response (as a reflection of es- 

 trogen secretion) if caged with other fe- 

 males, but will show enlarged oviducts when 

 caged with males (Folikarpova, 1940, cited 

 l)y Lehrman, 1959). This response may be 

 partly the result of the nest building which 

 is largely done by the male. It may thus 

 have been the nest built by the male rather 

 than the male per se to which the female re- 

 sponded. Burger (1953) observed that cag- 

 ing female starlings with males increased 

 the response of testes to light. 



Captivity prevents ovarian development 

 in pintail ducks. Anas acuta, captured from 

 migrating flocks while spermatogenesis in 

 the males is unimpaired (Phillips, 1959) . The 

 inhibition is mediated by way of the pitui- 

 tary, which, in the captive birds, contains 

 no detectable amounts of gonadotrophins. 

 Vaugien (1954a) found that wing clipping 

 of house sparrows, so that they could not 

 perch, prevented their testes from being 

 stimulated by light, as measured by sper- 

 matogenesis and l)ill color. The birds did 

 respond to PMS injections, suggesting that 



