GONADAL HORMONES AND SOCIAL BEHAVIOR 



1251 



link attacks other males in the spring, al- 

 though peaceful unisexual flocks are formed 

 when the breeding season wanes. Fighting 

 during the reproductive phase was reported 

 in the gentoo penguin, Pygoscelis papua 

 (Roberts, 1940) and in the herring gull, 

 Lams argentatus (Boss, 1943). 



Studies have been made which show a 

 cyclic relationship between changes in the 

 size of the gonads and the sequence of 

 social and reproductive behavior patterns 

 occurring before and during the breeding 

 season. Such a relationship is presumed to 

 be universal in seasonal breeders — the ex- 

 ception would be the cause celebre. Changes 

 in the grouping and dominance relations 

 among free ranging ring-necked pheasants 

 {Phasianus colchiciis) are related to sea- 



sonal increase in the weight of the testes 

 (Collias and Taber, 1951 j. During the 

 gonadal quiescence of winter the birds re- 

 main in marshes as small groups with shift- 

 ing memberships. Evidence of peck-orders 

 among cocks and hens was found. The 

 males pecked the females during competi- 

 tion for food. As the breeding season ad- 

 vanced there was a gradual increase in an- 

 tagonism between members of the same sex 

 and in attraction between individuals of 

 opposite sexes (Fig. 20.4). With an increase 

 in testis weight the male groups broke up, 

 territories were established, and harems 

 were formed. Cocks that ranked high in the 

 winter dominance order established ter- 

 ritories, whereas those of low social status 

 failed to do so. Genelly (1955) reported on 



PERIOD IN BREEDING CYCLE 



Transition Spring Dispersal Period 



period of period of 

 territory harem 

 ^stablishj Lformotionj 



Fig. 20.4. Expicssions of display or dominance between and within sexes of ring-necked 

 pheasants, from January through April. Broken lines represent infrequent occurrence; solid 

 line, frequent occurrence. The sequence of behavior changes is superimposed upon the in- 

 crease in testis size (Collias and Taber, 1951). 



