First, a skeleton can be the best proof because the turtle shell should be present. Further, turtles, unlike the birds, lay their eggs on the shores. Nests are buried in the sand because light can affect hatchlings. Also, the birds usually lay 2-3 eggs while turtles lay 2-8 eggs. So, if there is no turtle shell present, and the 6 eggs were in the nest covered with sand, it must be the turtle nest.