Anthropogenic noise: The effects of road noise on eavesdropping systems of the eastern chipmunk

Background/Question/Methods

With increasing human expansion, anthropogenic noise has been observed to negatively and dramatically affect many species globally. While various types of noise can have a wide array of affects, the predominant aspect that is the focus of this study is noise coming from roads.  Given the documentation of many species gathering information via heterospecific eavesdropping, we surmise that any additional noise put forth into an environment may affect and alter this process. In order to test this, we measured giving-up densities (GUDs) of eastern chipmunk (Tamias striatus) when exposed to various alarm calls and with and without the presence of road noise. Road noise was recorded and played back via a three-speaker line array spaced 25 meters apart. We placed two artificial food patches of varying resource density were placed at varying distances away from the speaker array and in a concentric pattern spaced 20 meters away from a fourth speaker which produced the various alarm calls. We then collected foraging data from these food patches over the course of 10 days with one alarm call treatment played back per day.  

Results/Conclusions

Our results demonstrate that chipmunks perceive their highest assessment of risk when heterospecific mobbing calls and high-threat alarm calls were played without road noise.  However when road noise was introduced, GUDs of the chipmunks were highest when presented with heterospecific mobbing calls and conspecific calls.  Chipmunks experienced lower threat assessment when exposed to road noise and high-threat heterospecific alarm calls.   These types of calls are produced when threat of predation is imminent. We surmise that with increased anthropogenic noise, particularly from roads, chipmunks may experience higher chronic levels of perceived predation risk.  With an increase in the amount of anthropogenic noise in a given environment, we expect to see an increase in population level effects of temperate forest species.