Effects of Urban Noise on Song Structure in a Sedentary and a Migratory Bird Species
Many animal species are dependent upon vocal communication to mate and defend territories. Selection will favor individuals that produce vocalizations that transmit best in their environments. The sensory drive concept suggests that environmental conditions, such as ambient sound, will influence the evolution of vocal behavior. Thus, background noise levels may have a profound effect on communication. We study how urban noise affects the cultural evolution of birdsong in two species: the migratory white-crowned sparrow (Zonotrichia leucophrys gambelii) and the sedentary house finch (Carpodacus mexicanus). These two species are ideal study organisms because they each have one song type, are territorial, and are easy to identify. We recorded songs and ambient noise concurrently across the Fresno-Clovis Metropolitan Area (FCMA) and in outlying rural areas for comparative analysis of acoustic properties, in particular the frequency and temporal structure of songs. Because song influences fitness via phenotypic and genotypic mate quality, understanding how song changes in an urban environment may allow us to predict species adaptability in a changing world.
White-crowned sparrows and house finches are amongst the most studied birds in terms of song analysis because of their use of song, mate territoriality and behavior, and easiness to identify. Similarly, within the last ten years, more research has been done to determine the effects of ambient urban noise to bird song structure (Wood et al. 2009; Katti & Warren 2004). However, although past studies have been shown to find an effect on bird songs of some species (i.e. Great Tits) due to ambient noise, the said studies only look at one variable accounting for song structure, frequency, yet none analyze the other variable of time (Fernandez-Juricic et al. 2005; Slabbekoorn & den Boer-Visser 2006).
The concept of Reconciliation Ecology has been gaining more and more scientific momentum for the past fifteen years because of its ability to integrate the human urban environment into the framework of ecological conservation. Where traditional conservation aims at protecting the 5-10% of land and, ultimately, native species not being affected by human development, reconciliation ecology focuses more on the 90-95% of anthropogenic land in an attempt to create a more suitable ecosystem that promotes biodiversity (Rosenzweig, 2003). However, in order to create a system that integrates this idea, one must first understand the effects that human ecosystems (i.e. urban area) have on natural systems.
The FCMA has an exceptional range of diversity in terms of land within and adjacent to its borders. Within the last six years efforts have been made in keeping track of the biodiversity that is, and can be, maintained in this urban setting. Habitat surveys pertaining to FCMA’s fauna and flora have been under effect to determine the scale of biodiversity that the area contains. Our studies with white-crowned sparrows and house finches aim in providing the area, and the scientific community, with new information that can shed more light and sound to the question regarding the effect of urban habitats to animal behavior.
