Challenges of Defining Existing (Traffic) Noise Near Protected Species Habitat

The Gunnison Sage Grouse is the first new bird species recognized in the United States since the 19th century. It is a listed threatened species that lives primarily in southwestern Colorado and Utah. This bird is remarkable for its elaborate courtship rituals, which male birds perform in early morning and evening during the spring; when they gather to perform this ritual the groups of male birds are called leks. A utility construction project was proposed to occur under a roadway that traverses Gunnison Sage Grouse brooding habitat, and encroaches upon leking areas. The United States Fish and Wildlife Service (USFWS) advocated that construction noise should be limited to an exceedance of existing noise levels by less than ten decibels. Increases of more than 10 decibels above existing noise levels are thought to interfere with Gunnison Sage Grouse communications. Existing noise is dominated by traffic noise in the study area. This paper discusses the different methods used by USFWS and HDR to evaluate existing traffic noise levels, and the challenges of using those methods. Construction noise levels were also estimated, and the potential increase above existing noise is discussed.