5.1. Hormonal Influences on Acoustic Perception:
Behavioral Evidence
Song perception by male and female birds may be influenced by circulating hormones. Both sexes use songs to distinguish conspecifics from heterospecifics. In red-winged blackbirds, sexually receptive females typically
respond to courting males with copulation solicitation displays, an avian
equivalent of lordosis in female rodents, whereas males respond to songs
of other males by aggressive behavior, including singing and physical
attacks (Searcy and Brenowitz 1988). When male and female blackbirds
were presented with conspecific male songs and imitation songs sung by the
mockingbird Mimus polyglottos (mockingbirds mimic songs of red-winged
blackbirds superbly well), female blackbirds showed a copulation solicitation response only to genuine conspecific songs, whereas males showed an
aggressive response both to conspecific and imitation songs. Although the
apparent sex difference in the responsiveness to conspecific and heterospecific songs may be ascribed to the differences in motivation to respond
or the amount of attention paid, one explanation is that the two sexes differ
in their perceptual capability to distinguish conspecific from heterospecific
songs. If this is the case, steroid hormones may be involved in the perception of conspecific songs in blackbirds.
In addition to conspecific recognition, the ability to recognize individuals using songs may also show sex differences. Male songs typically show
subtle intraspecific variation in acoustic properties. Female songbirds
choose a male partly based on features of his courtship song (Eriksson and
Wallin 1986), and males distinguish neighboring from stranger males using
their songs (Falls 1982). Cynx and Nottebohm (1992a) trained male and
female zebra finches to discriminate conspecific and heterospecific songs
using an operant-conditioning paradigm. Males required fewer trials than
females to discriminate conspecific songs, and both sexes learned to discriminate songs with fewer trials in the spring than in winter. Moreover, discrimination of various conspecific songs was enhanced when T was given
to castrated males (Cynx and Nottebohm 1992b). Thus, circulating T may
regulate discrimination of conspecific songs in zebra finches.
Ample evidence from human psychophysical studies supports the idea
that acoustic perception is influenced by circulating hormones. For example,
glucocorticoids, hormones secreted from the adrenal cortex in response to
stress, modify auditory perception in humans by elevating the perceptual
threshold (e.g., Henkin and Daly 1968; Fehm-Wolfdorf and Nagel 1996).
Gonadal steroids may also bias acoustic perceptions. Women have greater
auditory sensitivity than men in general, the auditory perception of women
is slightly masculinized during the first half of the menstrual cycle, and
women with twin brothers tend to have masculinized auditory perception
compared with women with twin sisters (reviewed by McFadden 1998).
These studies suggest that gonadal steroids could have organizational and
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A. Yamaguchi and D.B. Kelley
Behavioral Evidence
Song perception by male and female birds may be influenced by circulating hormones. Both sexes use songs to distinguish conspecifics from heterospecifics. In red-winged blackbirds, sexually receptive females typically
respond to courting males with copulation solicitation displays, an avian
equivalent of lordosis in female rodents, whereas males respond to songs
of other males by aggressive behavior, including singing and physical
attacks (Searcy and Brenowitz 1988). When male and female blackbirds
were presented with conspecific male songs and imitation songs sung by the
mockingbird Mimus polyglottos (mockingbirds mimic songs of red-winged
blackbirds superbly well), female blackbirds showed a copulation solicitation response only to genuine conspecific songs, whereas males showed an
aggressive response both to conspecific and imitation songs. Although the
apparent sex difference in the responsiveness to conspecific and heterospecific songs may be ascribed to the differences in motivation to respond
or the amount of attention paid, one explanation is that the two sexes differ
in their perceptual capability to distinguish conspecific from heterospecific
songs. If this is the case, steroid hormones may be involved in the perception of conspecific songs in blackbirds.
In addition to conspecific recognition, the ability to recognize individuals using songs may also show sex differences. Male songs typically show
subtle intraspecific variation in acoustic properties. Female songbirds
choose a male partly based on features of his courtship song (Eriksson and
Wallin 1986), and males distinguish neighboring from stranger males using
their songs (Falls 1982). Cynx and Nottebohm (1992a) trained male and
female zebra finches to discriminate conspecific and heterospecific songs
using an operant-conditioning paradigm. Males required fewer trials than
females to discriminate conspecific songs, and both sexes learned to discriminate songs with fewer trials in the spring than in winter. Moreover, discrimination of various conspecific songs was enhanced when T was given
to castrated males (Cynx and Nottebohm 1992b). Thus, circulating T may
regulate discrimination of conspecific songs in zebra finches.
Ample evidence from human psychophysical studies supports the idea
that acoustic perception is influenced by circulating hormones. For example,
glucocorticoids, hormones secreted from the adrenal cortex in response to
stress, modify auditory perception in humans by elevating the perceptual
threshold (e.g., Henkin and Daly 1968; Fehm-Wolfdorf and Nagel 1996).
Gonadal steroids may also bias acoustic perceptions. Women have greater
auditory sensitivity than men in general, the auditory perception of women
is slightly masculinized during the first half of the menstrual cycle, and
women with twin brothers tend to have masculinized auditory perception
compared with women with twin sisters (reviewed by McFadden 1998).
These studies suggest that gonadal steroids could have organizational and
308
A. Yamaguchi and D.B. Kelley