1258 



HORMONAL REGULATION OF BEHAVIOR 



either hormone were given daily to different 

 chicks for 30 days. The number of aggres- 

 sive pecks observed was proportional to the 

 dosage of androgen given to male chicks. 

 With the lower dosage, pecking was more 

 frequent than attempted matings. Testos- 

 terone was more effective than estradiol in 

 inducing aggressive behavior. Males were 

 much more responsive to the androgen than 

 females. Submissive behavior was not re- 

 ported. The conditions under which these 

 chicks were reared were not given, nor were 

 the dominance relations mentioned. 



Experiments to determine the approxi- 

 mate age at which chicks develop agonistic 

 behavior and establish a social order, and 

 the effects of gonadal hormones and social 

 inertia on the precocity of such behavior 

 were reported by Guhl (1958). In small 

 groups of chicks the males developed ag- 

 gressive behavior earlier than the females; 

 in mixed flocks there were heterosexual 

 peck-orders, with males pecking more fre- 

 quently than females. There was a gradual 

 trend toward unisexual pecking. Some 

 chicks were reared in partial isolation from 

 the second day after hatching and as- 

 sembled into groups when their respective 

 control flocks of the same sex established a 

 peck-order (8 to 9 weeks for males, 10 weeks 

 for females). These birds formed a peck- 

 order in a matter of hours, indicating that 

 it did not require 8 to 10 weeks of learning 

 to form a dominance order. This difference 

 between group-reared and assembled iso- 

 lation-reared birds may have been related 

 to either the maturation of the endocrine 

 and nervous systems, or it may be that so- 

 cial inertia in the group-reared chicks sup- 

 pressed the influences of developmental 

 processes thereby producing a time lag in 

 the evocation of agonistic behavior. 



As a part of the same investigation, in- 

 dividuals in small unisexual groups were in- 

 jected with either testosterone or diethyl- 

 stilbestrol. Each treated group was matched 

 with a control group from the same hatch. 

 In all but one group the injections were be- 

 gun the 2nd or 3rd day after hatching. Dom- 

 inance or subordination was established 

 somewhat earlier in the treated groups, de- 

 pending on the hormone used. The andro- 

 gen-treated chicks, irrespective of sex. 



showed increased aggressiveness, whereas 

 the estrogen-treated chicks, again irrespec- 

 tive of sex, were more submissive and the 

 social order was determined by the consist- 

 ent avoidance by each chick of speciflc pen- 

 mates. However, the differences between the 

 means of experimentals and controls are 

 small and do not suggest any marked pre- 

 cocity in agonistic behavior as a result of 

 treatment with gonadal hormones. 



In the same study (Guhl, 1958) capons 

 were used to determine the age at which 

 dominance-subordination relations (peck- 

 rights) may be established in the absence of 

 androgen (Table 20.1). For comparison 

 there was one group of normal males and 

 one group of capons receiving large dosages 

 of testosterone propionate daily (0.5 mg. 

 beginning the 10th clay which was increased 

 by 0.5 mg. weekly for 4 weeks) . Caponiza- 

 tion was on the 9th day of age, and therefore 

 the untreated capons had little or no en- 

 dogenous androgen (Breneman and Mason, 

 1951). The mean age at which the untreated 

 capons established peck-rights was 13.7 

 weeks, whereas the mean for the normal 

 males was 9.9 weeks, and for the treated 

 capons 7.8 weeks. It is of interest that a so- 

 cial order developed by the 17th week in 

 the apparent absence of androgen, and that 

 the high level of treatment enhanced the 

 formation of a peck-order over the controls 

 by only 1 week, the 12th week compared 

 with the 13th week for the normal males. 



VII. Releasers and Other Mechanisms 

 in Social Behavior 



Secondary sex characters such as adorn- 

 ment and color, postures, odors, and certain 

 sounds, have a place in the mediation of 

 social behavior and are thought to function 

 as releasers of specific behavior patterns. 

 Such stimuli may be simple or very com- 

 plex configurations (Tinbergen, 1951). 



In an excellent review of the behavior of 

 cichlid fishes, Baerends and Baerends-Van 

 Roon (1950) related chromatophores to be- 

 havior patterns. Six types of chromato- 

 phores were discussed showing various 

 methods of development and control. In 

 Tilapia natalensis the black reproductive 

 markings developed under the physiologic 

 conditions typical of the reproductive pe- 



