This paper focused on the effects of anthropogenic noise, urban structure, and vegetation on the song structure of a historically open habitated bird. They studied chipping sparrows, which evolved in an open grassland habitat. Species that evolve in closed environments, such as forests, tend to produce shorter and more tonal signals than those is open habitats, such as grasslands. This is because of attenuation and reverberation distorting sound and masking certain pitches and frequencies. Attenuation means that a sound will be fainter the further away from the source it becomes. Higher frequencies show a more excess attenuation than lower frequencies because they are more likely to be absorbed by the environment and they are more scattered since they are a higher energy, so they are more likely to be distorted in their path in the presence of a closed habitat. Degradation also plays a role in sound production as well and is more important in habitats with a lot of cover. Reflection and echoes make it difficult to differentiate different vocal elements.
This study focused on song sparrows in the closed habitat of an urban environment. Urbanization has a lot of anthropogenic noise, which is noise that has both a high amplitude and low frequency. This noise masks a lot of animal sounds and reduces the space that animals have to communicate. Built structures in urban areas are also highly reflective, sounds that reflect off of buildings in urban environments hold more energy than when they are reflected off of structures in forests because urban structures tend to be very smooth and flat in comparison so there is less sound absorption. Past studies show that