The ornate box turtle (Terrapene ornata ornata) is on the threatened species list in Iowa. Predation on nests is the primary source of mortality in this species; Cornell faculty and students have investigated interventions intended to reduce nest predation in a nearby population of ornate box turtles. According to Optimal Foraging Theory, organisms should forage in a method which maximizes their energy intake per unit time. If an area does not provide a sufficient payoff rate, the predator will move on to a new area. If this model is correct, saturating an area with many artificial nests should reduce predation rates on natural nests.
In June 2009, we conducted experiments at Hawkeye Wildlife Area in Johnson County, Iowa, to determine whether altering payoff rates would affect the rate at which predators excavate artificial nests. We established three replicates of each of three 10 x 10 meter arrays that differed in payoff rate. Arrays had 35, 60, or 100 artificial nests randomly assigned to locations in the array; of these, ten randomly selected nests in each array contained a chicken egg. Most artificial nests were excavated within a few days and there was minimal digging at locations where we had not made a hole. Kaplan-Meier survival analysis of the lifespan of artificial nests indicated no difference in depredation rates between empty and egg-containing nests, while excavation rate across all artificial nests was greatest in the 100 nest arrays. Thus, interspersing empty nests among real nests may actually increase predation rate.
Phillip Gallagher, ’11 Yorkville, IL
Majors: Environmental Studies, Classical Studies, Biology
Nicholas Campbell, ’11 West Liberty, IA
Majors: Environmental Studies, Geology
Amanda Gilbert, ’10 Bettendorf, IA
Majors: Biology, Environmental Science
Brock Nelson, ’11 Blue Grass, IA
S. Andrew McCollum
Sponsors: Robert Black and S. Andrew McCollum