No abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. We compared responses of males whose mates were fertile or nonfertile with differences in song structure (SRS vs. LRS and soft LRS), amplitude (SRS and soft LRS vs. LRS), and tempo (slow SRS vs. fast SRS). Males responded more strongly to SRS than to LRS or soft LRS, indicating that song structure had a greater effect on response than song amplitude. SRS tempo did not detectably affect male response. Importantly, males responded more strongly to SRS when their mates were fertile, presumably because hearing SRS can indicate that a male's mate is being courted by an intruding male and a strong response can deter extrapair competitors. We conclude that lowamplitude songs can function in both inter-and intrasexual communication and should receive greater attention in future studies of mate choice and male-male competition.

Acoustic signaling is a taxonomically widespread form of animal communication consisting of long range, high-amplitude signals and short range, low-amplitude signals. Research on acoustic communication has emphasized high-amplitude signals and often overlooked low-amplitude signals, even though they are produced in behavioural contexts that directly influence fitness. Low-amplitude signals are referred to by a variety of names such as soft songs, courtship songs, whispers, close calls, contact calls, grunts, and moans, but all of these signals share a reduced amplitude and an active space that is limited to close-proximity receivers. In this review, we establish a general definition for low-amplitude signals and investigate the similarities and differences between low-and high-amplitude signals with respect to their acoustic structure and function. Then, we critically evaluate some proximate and ultimate evolutionary mechanisms that may explain why these signals are produced at low amplitude using examples from a variety of taxa. We conclude by suggesting priorities for future research on low-amplitude signals and highlighting how studying these signals will lead to a more complete understanding of how and why animals communicate acoustically.

No abstract

Environmental changes caused by urbanization and noise pollution can have profound effects on acoustic communication. Many organisms use higher sound frequencies in urban environments with low-frequency noise, but the developmental and evolutionary mechanisms underlying these shifts are less clear. We used a common garden experiment to ask whether changes in minimum song frequency observed 30 years after a songbird colonized an urban environment are a consequence of behavioral flexibility or canalized changes that occur early in development. We captured male juvenile dark-eyed juncos (Junco hyemalis thurberi) from two recently diverged populations (urban and mountain) soon after they reached independence (aged 25-40 days), raised them in identical indoor aviaries, and studied their songs at an age of three years. We found that the large population difference in minimum frequency observed in the field persisted undiminished in the common garden despite the absence of noise. We also found some song sharing between the common garden and natal field populations, indicating that early song memorization before capture could contribute to the persistent song differences in adulthood. These results are the first to show that frequency shifts in urban birdsong are maintained in the absence of noise by genetic evolution and/or early life experiences..