American beavers are foragers with a central home location that make foraging trips from their lodge and then return. To test the optimal foraging theory, researchers trapped and radio-tagged a random sample of 67 American beavers from the population in a certain region and recorded their movements over the course of about a year. The researchers fit a least-squares regression line to the data, where the explanatory variable was distance to lodge, in meters, and the response variable was speed, in meters per hour. The resulting residual plot of the regression analysis is shown.