Past studies show that species tend to increase their maximum frequency of signals as noise increases in an attempt to minimize the amount of their noise that would be masked by the increase in noise. This however, is contradicted by the idea that urban structure would select for lower frequency signals because lower frequencies have a better ability to bend around structures and are less prone to reverberation and they are less likely to develop echoes.
In this, they focused on male chipper sparrows when they broadcast songs to females specifically. They were curious as to whether chipper sparrows with different song variants would adjust their songs differently to an increase in both noise and structure, whether noise and structure affected different features of song, and if vocal performance was affected by noise and structure. They looked at species in urban environments to explore how individuals in the same population responded to noise and structure, they wanted to know if they would respond in a similar way. They found that male sparrows fell into two different categories. The second group had higher trill rates, lower maximum frequency, narrower bandwidths, and higher trill rates than the first group. They predicted that the first group of sparrows would increase their minimum frequency in the presence of more noise in order to minimize the masking and decrease their maximum frequency in the presence of increased structure to maximize reverberation. They did not expect any change in temporal traits. They expected group two males that had higher trill rates to decrease their trill rate with increasing structure but they did not expect any changes in response to noise. This is because they were already not susceptible to noise masking from the environment.