Singing in the city: Trade-offs between signal salience and vocal performance in the presence of anthropogenic noise

Abstract

Many animals use acoustic signals to communicate. Signals specifically used to compete for or select a mate are under sexual selection. Selection therefore favors signaling traits that indicate competitive ability or mate quality. For example, performance of signaling traits that are costly to produce, such as those that are physically limited by the animal's size or coordination are more likely to convey honest information about the sender. Selection also favors signaling traits that maximize the transmission of this information in a given environment. For example, other sounds in the environment (the soundscape) can reduce the ability of individuals to detect or decode information in the signal. However, individuals may not always be able to maximize both performance and transmission of a signal. This leads to two critical questions—when faced with this trade-off, which aspect of the signal do senders maximize and how does this decision affect communication? I address these questions using a well-studied sexual signal—bird song—in anthropogenic soundscapes, which are evolutionarily recent selective environments. Here, I tested whether vocal performance functions in male-male competition in White-crowned Sparrows (Zonotrichia leucophrys), and how assessment of performance varies across different urban and rural soundscapes in San Francisco and Point Reyes, California. I also investigate how soundscapes go beyond individual behavior and affect survival of these populations.