Prediction of the Onset of the Annual Nesting Season of the Common Snapping Turtle, Chelydra serpentina

Accumulation of heat units in a lake was used to predict the onset of the annual nesting period for a population of Chelydra serpentina in north-central Ontario. Date of the first nesting attempt varied by 15 days over 6 yr, but number of heat units accumulated prior to the first nesting attempt varied by only 7.5%. By computing heat unit values, we were able to predict the date of the first nesting attempt within one day in each of 4 yr. Therefore, this method should be valuable in determining the start of nesting in a study population and in assessing local climatic (temperature) effects on the timing of oviposition.