Mountain gorilla ranging patterns: influence of group size and group dynamics.

Since the 1980s, the Virunga mountain gorilla population has almost doubled, now reaching 480 individuals living in a 430-km(2) protected area. Analysis of the gorillas' ranging patterns can provide critical information on the extent and possible effects of competition for food and space. We analyzed 12 years of daily ranging data and inter-group encounter data collected on 11 gorilla groups monitored by the Karisoke Research Center in Rwanda. During that period, the study population increased in size by almost 50% and the number of groups tripled. Groups had small yearly home ranges compared to other known gorilla populations, with an average 90% kernel density estimate of 8.07 km2 and large between-group variations (3.17-23.59 km2). Most groups had consistent home range location over the course of the study but for some, we observed gradual range shifts of up to 4 km. Neighboring groups displayed high home range overlap, which increased dramatically after the formation of new groups. On average, each group used only 28.6% of its 90% kernel home range exclusively, and in some areas up to six different groups had overlapping home ranges with little or no exclusive areas. We found a significant intra-group positive relationship between the number of weaned individuals in a group and the home range size, but the fitted models only explained 17.5% and 13.7% of the variance in 50% and 90% kernel home range size estimates, respectively. This suggests that despite the increase in size, the study population is not yet experiencing marked effects of feeding competition. However, the increase in home range overlap resulting from the formation of new groups led to a sixfold increase in the frequency of inter-group encounters, which exposes the population to elevated risks of fight-related injuries and infanticide.

Estimating the proportion of children who can walk to school.

BACKGROUND: Walking to school can be an important contributor to the daily physical activity of children. However, little is known about the percentage of children who could reasonably be expected to walk to school. The purpose of this study was to estimate the percentage of children in Georgia who live within a safe and reasonable walking distance from school and to identify demographic, school, and neighborhood connectivity characteristics associated with the potential to walk to school. METHODS: Geographic information systems techniques were used to estimate the number of school-age children living 1 mile and 0.5 mile from public schools in Georgia. Potential walkers were estimated by dividing the number of children living in the specified distances from school in the 2000 U.S. Census by the number of children enrolled at the school in the 1999-2000 school year. Safety parameters were based on posted speed limits. RESULTS: The percentage of potential walkers ranged from 1% to 51% depending on grade group and parameters of distance and safety. Using preferred parameters of distance and safety we estimated that 6% of elementary school students (K-5), 11% of middle school students (6 to 8), and 6% of high school students could walk to school. High population density, small enrollment size, and high street connectivity were associated with higher percentages of potential walkers. CONCLUSIONS: While few children could reasonably be expected to walk, this does not reduce the value of walking to school. Increasing the percentage of students who walk will require both educational efforts and changes to the built environment.