PHOTOPERIODIC CONTROL OF ANNUAL 

 GONADAL CYCLES IN BIRDS 



DONALD S. FARNER 

 State College of Washington, Pullman 



This discussion is concerned primarily with photoperiodic controls of 

 the annual gonadal cycles of certain Temperate Zone species of birds. 

 Because of the investigations in our laboratories, special attention will 

 be directed at times toward the cycle of a migratory race of white- 

 crowned sparrow, Zonotrichia leuchophrys gambelii.^ This emphasis 

 gives the advantages of direct knowledge and availability of illustra- 

 tive material. Nevertheless, very extensive use will be made of the 

 results of other investigations on different species, for the advantages 

 of both comparison and completeness. This will have the effect of 

 creating a composite picture of many aspects of the phenomenon. It 

 must be borne in mind that the creation of such composite pictures is 

 somewhat hazardous since it is probable that photoperiodic control 

 mechanisms among birds may be polyphyletic in origin and that there 

 may be basic differences among the control mechanisms of various 

 species. This discussion, except for a few comparisons which appear 

 appropriate, will not consider the mechanism of the photoperiodically 

 induced increase in qoo production in the domestic fowl. This decision 

 is made not only because photoperiodism in the female domestic fowl 

 is the subject of another paper in this symposium, but also because 

 this mechanism in a domestic species of essentially tropical origin may 

 be only superficially similar to that of Temperate Zone wild species. 

 It must be borne in mind constantly that, for the species under con- 

 sideration, the gonadal cycle obviously is only one of a complex of 



* These investigations have been supported by the Office of Naval Research, 

 Contract Nonr 1520(00), and by funds made available for biological and 

 medical research by the State of Washington Initiative Measure No. 171. I 

 wish to acknowledge with sincere gratitude the invaluable contributions of 

 L. R. Mewaldt, Andreas Oksche, J. R. King, A. C. Wilson, Donald Laws, R. D, 

 McGreal, S. D. Irving, and Conrad A. Donovan. 



717 



