1. Introduction
Several hours after twilight, on a hot summer night in June, a female bullfrog, Rana catesbeiana, swims in the shallow waters of a Rhode Island pond.
Periodically, she raises her head above the water level and appears to listen
to a cacophony of sounds around her, including the advertisement calls of
male bullfrogs, advertisement calls of male green frogs (Rana clamitans),
the buzzing of insects, the prowling of raccoons and cats around the pond’s
edges, shouts and laughter of humans nearby, music, traffic noise, wind
noise, and the low rumble of airplanes flying overhead. Through the water
come additional sounds, including those of fish, turtles and insects. After a
time of seemingly random swimming, the female bullfrog approaches a
calling male bullfrog and mates with him. After amplexus is complete, the
female deposits her eggs, and the male resumes calling.
This seemingly simple and straightforward instance of acoustic communication requires a great deal of sophisticated biological and psychological
processing by the animals involved. Temperate-zone frogs in their natural
habitats only breed during the summer, and then only when rainfall and
temperature are appropriate. Because mating is seasonal, these animals
must have a mechanism for detecting environmental conditions. In addition, mating only occurs when both the female and the male are hormonally ready. Their hormonal control systems must thus have access to
environmental sensors in order to coordinate internal events with the external milieu. The female’s task is to identify and choose among males of her
own species using acoustic cues embedded in a complex, noisy environment.
She must be able to identify and separate sounds conveying the message of
“bullfrog advertisement calls” from those conveying irrelevant messages
such as “a motorcycle is going by.” Not only must the female discriminate
between conspecific bullfrog males and heterospecific green frog males, but
she also needs to distinguish among the different types of calls (advertisement, aggressive, territorial) within the male bullfrog’s repertoire. Moreover, the female may target particular individual males within the larger
1
1
Perspectives and Progress in
Animal Acoustic Communication
Andrea Megela Simmons
Several hours after twilight, on a hot summer night in June, a female bullfrog, Rana catesbeiana, swims in the shallow waters of a Rhode Island pond.
Periodically, she raises her head above the water level and appears to listen
to a cacophony of sounds around her, including the advertisement calls of
male bullfrogs, advertisement calls of male green frogs (Rana clamitans),
the buzzing of insects, the prowling of raccoons and cats around the pond’s
edges, shouts and laughter of humans nearby, music, traffic noise, wind
noise, and the low rumble of airplanes flying overhead. Through the water
come additional sounds, including those of fish, turtles and insects. After a
time of seemingly random swimming, the female bullfrog approaches a
calling male bullfrog and mates with him. After amplexus is complete, the
female deposits her eggs, and the male resumes calling.
This seemingly simple and straightforward instance of acoustic communication requires a great deal of sophisticated biological and psychological
processing by the animals involved. Temperate-zone frogs in their natural
habitats only breed during the summer, and then only when rainfall and
temperature are appropriate. Because mating is seasonal, these animals
must have a mechanism for detecting environmental conditions. In addition, mating only occurs when both the female and the male are hormonally ready. Their hormonal control systems must thus have access to
environmental sensors in order to coordinate internal events with the external milieu. The female’s task is to identify and choose among males of her
own species using acoustic cues embedded in a complex, noisy environment.
She must be able to identify and separate sounds conveying the message of
“bullfrog advertisement calls” from those conveying irrelevant messages
such as “a motorcycle is going by.” Not only must the female discriminate
between conspecific bullfrog males and heterospecific green frog males, but
she also needs to distinguish among the different types of calls (advertisement, aggressive, territorial) within the male bullfrog’s repertoire. Moreover, the female may target particular individual males within the larger
1
1
Perspectives and Progress in
Animal Acoustic Communication
Andrea Megela Simmons