The methodologies and indicators used by TRPA to evaluate the attainment status of the waterfowl standard has varied over time. The 2001 Threshold Evaluation Report used observed bird species richness and diversity along with the human activity rating system to gage threshold standard attainment status (TRPA 2001). The 2006 Threshold Evaluation Report used observation of bird species richness and diversity as well as an assessment of detrimental or non-native species, but did not use the human disturbance rating system that was used in 2001. The 2011 Threshold Evaluation Report used only a human disturbance rating system as a means to measure status (TRPA 2012a). Similar to the 2011 Threshold Evaluation Report, the 2015 assessment is based on field observations and human activity levels at mapped waterfowl population sites. The 2015 survey was a rapid assessment where no formal waterfowl surveys were conducted. For the human disturbance rating evaluation, each site was visited by a qualified observor.