4. HORMONES AND BEHAVIOR
217
must be adequate to account for postnuptial as well as prenuptial migration and for the fact that some species migrate from areas north of the
equator whereas others start from south of the equator.
The results of early attempts to follow the activity of trapped birds
after gonadectomy and release (219-222) were believed to support the
view that migration is not associated with the state of the gonads, but
Bullough (214) comments with good reason that these results are inconclusive. Measurement of the nocturnal restlessness, Zugunruhe, displayed
twice a year by migratory birds (217, 223, 224) has been used widely
in a laboratory approach to the problem. Attention has been given also
to the accumulation of fat which precedes the development of Zugunruhe
(225, 226). The extent to which these phenomena are concomitants of
migration and the degree to which they are under hypothalamic, hypophyseal, and gonadal control are mooted points. Farner (215, 227)
and Farner et al. (223) discount the role of gonads in favor of the notion
that nongonadotropic effects of the anterior pituitary are primary.
Marshall (217) doubts that rejection of the idea that the sex hormones
are directly involved can be justified. He reminds us that fat deposition
does not occur in all migratory species, that it can be induced by photostimulation, gonadotropins, and testosterone, and finally that certain
critical experiments have not been performed, e.g., measurement of the
nocturnal activity in hypophysectomized postnuptial migrants in the
autumn, and of this activity in hypophysectomized light-stimulated
prenuptial migrants in the spring.
The relationship of the hormones to mating behavior, aggressive
behavior, and territorial defense in male birds is not controversial (4,
228-231). Except for aggressive behavior in the starling (232), these
types of behavior disappear or are displayed in reduced strength following gonadectomy, and restoration follows administration of testosterone.
The many correlations of interstitial cell development with seasonal
activity (230, 233) and the evidence from histochemical studies (230,
234) are the basis for the conclusion that interstitial cells are the principal source of this androgen.
Unsolved problems exist, but they are not unlike those encountered
in the other vertebrate phyla—the relatively slow decline in the strength
of mating activity following castration (235, 236), the persistence of
many elements of the pattern after castration (235, 237-239), the apparently complete pattern of masculine behavior exhibited by one
gonadectomized hybrid pigeon (240), the site of hormone action, and
the mechanism by which androgens exert their effects.
One problem may be more specific for birds, although it is encountered in other phyla. Males of some species normally perform or
217
must be adequate to account for postnuptial as well as prenuptial migration and for the fact that some species migrate from areas north of the
equator whereas others start from south of the equator.
The results of early attempts to follow the activity of trapped birds
after gonadectomy and release (219-222) were believed to support the
view that migration is not associated with the state of the gonads, but
Bullough (214) comments with good reason that these results are inconclusive. Measurement of the nocturnal restlessness, Zugunruhe, displayed
twice a year by migratory birds (217, 223, 224) has been used widely
in a laboratory approach to the problem. Attention has been given also
to the accumulation of fat which precedes the development of Zugunruhe
(225, 226). The extent to which these phenomena are concomitants of
migration and the degree to which they are under hypothalamic, hypophyseal, and gonadal control are mooted points. Farner (215, 227)
and Farner et al. (223) discount the role of gonads in favor of the notion
that nongonadotropic effects of the anterior pituitary are primary.
Marshall (217) doubts that rejection of the idea that the sex hormones
are directly involved can be justified. He reminds us that fat deposition
does not occur in all migratory species, that it can be induced by photostimulation, gonadotropins, and testosterone, and finally that certain
critical experiments have not been performed, e.g., measurement of the
nocturnal activity in hypophysectomized postnuptial migrants in the
autumn, and of this activity in hypophysectomized light-stimulated
prenuptial migrants in the spring.
The relationship of the hormones to mating behavior, aggressive
behavior, and territorial defense in male birds is not controversial (4,
228-231). Except for aggressive behavior in the starling (232), these
types of behavior disappear or are displayed in reduced strength following gonadectomy, and restoration follows administration of testosterone.
The many correlations of interstitial cell development with seasonal
activity (230, 233) and the evidence from histochemical studies (230,
234) are the basis for the conclusion that interstitial cells are the principal source of this androgen.
Unsolved problems exist, but they are not unlike those encountered
in the other vertebrate phyla—the relatively slow decline in the strength
of mating activity following castration (235, 236), the persistence of
many elements of the pattern after castration (235, 237-239), the apparently complete pattern of masculine behavior exhibited by one
gonadectomized hybrid pigeon (240), the site of hormone action, and
the mechanism by which androgens exert their effects.
One problem may be more specific for birds, although it is encountered in other phyla. Males of some species normally perform or