Male eastern box turtles can bite, shove, and head butt. Image: Mass Audubon Wellfleet

At first, it appears that two turtles with yellow spots are calmly sitting side by side. Suddenly, one of them turns, slowly—and lunges out with its head, its open beak clearly trying to take an aggressive chomp out of its neighbor. Moments later, the turtle tries again. Now, both reptiles are going head-to-head, though each is retracted into the protection of its shell.

The two combatants are male eastern box turtles ( Terrapene carolina carolina ) competing for dominance. Eastern box turtles are a subspecies of the common box turtle ( Terrapene carolina ), with bright orange and yellow coloring on its dark shell.…