3.4. Alarm Calls
Alarm calls are ubiquitous vocalizations given in response to detecting a
predator. One would expect that this emergency vocalization should not
require a particular endocrine profile because it should take precedence
over other needs in life. However, in domestic fowl, aerial alarm calls,
emitted in response to seeing a predator overhead, increase with circulating levels of T; castrating males decreases the rate of alarm calling, whereas
T implants increase the calling rate (Gyger et al. 1988). In addition, male
domestic fowl give more alarm calls than females do. It is not clear from
this study, however, whether T activates alarm calling per se or enhances
alertness or motivation to vocalize in general.
4. Organizational Effect of Hormones on
Acoustic Signal Production
The physiological substrates for vocal production are organized by hormones during development. The organizational role of hormones is most
striking in sexually differentiated vocal systems. Sexual dimorphism is a
characteristic feature of systems that subserve courtship and aggressive
vocalizations; both the vocal organ itself and CNS pathways can differ dramatically in males and in females. Some sex differences are due to hormones that circulate in adulthood. Most, however, are due to the effects of
hormones during early stages of development. In the vocal periphery,
androgens stimulate cell proliferation, control cell types, and masculinize
organogenesis. In the central nervous system, the best-documented effect
of androgens is the prevention of ontogenetic cell death. In this section, we
will review how hormones organize the central vocal pathways and the
peripheral vocal organs in males and females.
4.1. Birds
In most songbirds in the temperate zone, males produce songs, whereas
females sing much less frequently or not at all. Males and females have
similar numbers of muscle fibers in the syrinx and similar numbers of
neurons in the vocal motor nucleus (the hypoglossus). In vocal-control
regions of the telencephalon, however, dramatic sex differences are found
(Nottebohm and Arnold 1976); males not only have more cells than females
but also have different sets of connections between CNS vocal nuclei. These
sex differences are attributable to specific developmental programs of
males and females. Song nuclei of female zebra finches can be masculinized
if exogenous estrogen is given around the time of hatching; masculinized
females go on to produce male-like songs when adult (Gurney 1981, 1982;
Adkins-Regan and Ascenzi 1987; Simpson and Vicario 1991). Most of the
6. Hormonal Control of Communication
301
Alarm calls are ubiquitous vocalizations given in response to detecting a
predator. One would expect that this emergency vocalization should not
require a particular endocrine profile because it should take precedence
over other needs in life. However, in domestic fowl, aerial alarm calls,
emitted in response to seeing a predator overhead, increase with circulating levels of T; castrating males decreases the rate of alarm calling, whereas
T implants increase the calling rate (Gyger et al. 1988). In addition, male
domestic fowl give more alarm calls than females do. It is not clear from
this study, however, whether T activates alarm calling per se or enhances
alertness or motivation to vocalize in general.
4. Organizational Effect of Hormones on
Acoustic Signal Production
The physiological substrates for vocal production are organized by hormones during development. The organizational role of hormones is most
striking in sexually differentiated vocal systems. Sexual dimorphism is a
characteristic feature of systems that subserve courtship and aggressive
vocalizations; both the vocal organ itself and CNS pathways can differ dramatically in males and in females. Some sex differences are due to hormones that circulate in adulthood. Most, however, are due to the effects of
hormones during early stages of development. In the vocal periphery,
androgens stimulate cell proliferation, control cell types, and masculinize
organogenesis. In the central nervous system, the best-documented effect
of androgens is the prevention of ontogenetic cell death. In this section, we
will review how hormones organize the central vocal pathways and the
peripheral vocal organs in males and females.
4.1. Birds
In most songbirds in the temperate zone, males produce songs, whereas
females sing much less frequently or not at all. Males and females have
similar numbers of muscle fibers in the syrinx and similar numbers of
neurons in the vocal motor nucleus (the hypoglossus). In vocal-control
regions of the telencephalon, however, dramatic sex differences are found
(Nottebohm and Arnold 1976); males not only have more cells than females
but also have different sets of connections between CNS vocal nuclei. These
sex differences are attributable to specific developmental programs of
males and females. Song nuclei of female zebra finches can be masculinized
if exogenous estrogen is given around the time of hatching; masculinized
females go on to produce male-like songs when adult (Gurney 1981, 1982;
Adkins-Regan and Ascenzi 1987; Simpson and Vicario 1991). Most of the
6. Hormonal Control of Communication
301