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ABSTRACT
Singing by white-throated sparrows Zonotrichia albicollis during
the winter in natural situations occurred most frequently among birds
with high rank in a dominance hierarchy. Genetic morph, age and sex had
no significant influence on singing duri ng winter. Among
testosterone-implanted birds in small groups in large aviaries, dominance
rank strongly influenced singing. Testosterone-treated birds with top
rank sang most frequently, those with second rank less, and those with
lower rank never. As a testosterone-treated bird's rank changed in the
course of regroupings with new opponents, its frequency of singing also
changed.
Dominance in a group thus interacted with testosterone to promote
singing. In addition, grouped birds in May before treatment with
testosterone did not sing. As a consequence, it seems likely that the
normal seasonal development of territorial behavior
and singing involves cascading influences of endocrine states and social
circumstances.
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CONCLUSIONS
Our results with white-throated sparrows have suggested a number
of interactions between social situation and hormonal state in the
control of singing. In this species testosterone does not invariably
activate singing. Instead, testosterone interacts w ith dominance to
promote singing. Furthermore, some isolation from frequent encounters
with rivals, such as that provided by dominance within a territory,
evidently contributes to full endocrine development.
Many previous studies, mostly on socially isolated birds, have
suggested that gonadal recrudescence leads directly to territoriality and
singing. Our results here suggest that seasonal endocrine and behavioral
development might instead be a cascading in teraction between hormonal
effects on social behavior and social effects on hormonal activity.
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