This study, conducted by Dr. John B. Calhoun, explores the ecology and sociology of the Norway rat (Rattus norvegicus) over a 27-month period in a quarter-acre enclosure designed to simulate the rat's natural habitat. The study aims to understand how social interactions influence population growth and behavior. Key findings include: 1. **Environmental Conditions**: The enclosure was designed to mimic the typical habitat of the Norway rat, including burrow systems, trails, and space utilization. 2. **Social Behavior**: The study observed various social behaviors such as burrow construction, trail formation, and interactions among individuals. Social relationships and dominance were found to influence mortality rates and population dynamics. 3. **Reproduction and Growth**: The growth of individuals and the colony was studied, with observations on sexual behavior, reproduction, and the impact of stress on growth. 4. **Health and Mortality**: The health and mortality of the rats were recorded, including the effects of predation, food availability, and environmental factors. 5. **Environmental Control**: The study also explored the effectiveness of environmental controls, such as barriers and food sources, in managing rat populations. The research provides insights into the complex social and ecological interactions of the Norway rat, highlighting the importance of social interactions in shaping population dynamics and behavior. The study was conducted under the auspices of the Johns Hopkins University School of Hygiene and Public Health and was supported by the Rockefeller Foundation.This study, conducted by Dr. John B. Calhoun, explores the ecology and sociology of the Norway rat (Rattus norvegicus) over a 27-month period in a quarter-acre enclosure designed to simulate the rat's natural habitat. The study aims to understand how social interactions influence population growth and behavior. Key findings include: 1. **Environmental Conditions**: The enclosure was designed to mimic the typical habitat of the Norway rat, including burrow systems, trails, and space utilization. 2. **Social Behavior**: The study observed various social behaviors such as burrow construction, trail formation, and interactions among individuals. Social relationships and dominance were found to influence mortality rates and population dynamics. 3. **Reproduction and Growth**: The growth of individuals and the colony was studied, with observations on sexual behavior, reproduction, and the impact of stress on growth. 4. **Health and Mortality**: The health and mortality of the rats were recorded, including the effects of predation, food availability, and environmental factors. 5. **Environmental Control**: The study also explored the effectiveness of environmental controls, such as barriers and food sources, in managing rat populations. The research provides insights into the complex social and ecological interactions of the Norway rat, highlighting the importance of social interactions in shaping population dynamics and behavior. The study was conducted under the auspices of the Johns Hopkins University School of Hygiene and Public Health and was supported by the Rockefeller Foundation.