Daily and seasonal variation in hydric conditions and temperature inside nests of common snapping turtles (Chelydra serpentina)

Abstract

Water potential and temperature are interrelated variables that must be studied simultaneously to gain insight concerning the water relations of reptilian eggs incubating in subterranean nests. We measured these variables inside nests of common snapping turtles (Chelydra serpentina) using thermocouple psychrometry. Water potentials in nests were high after heavy rainfalls, but declined during periods of fair weather. Likewise, temperatures in nests increased progressively during intervals of warm weather, but declined abruptly during cool periods accompanied by overcast and precipitation. On clear days, diel cycles in temperature occurred at the top, in the middle, and at the bottom of nests, but the cycles were slightly out of phase and their amplitudes decreased with increasing depth. These cycles in temperature drove cycles in evaporation–condensation of water that led in turn to complex cycles in diffusion of vapour. Net movement of vapour was into nests on some occasions, but out of them on others. Transport of liquid occurred also in the vicinity of nests, but probably was less important than transport of vapour as a means for translocating water. The eggs themselves influenced water potentials and vapour pressures in the vicinity of their nests and thereby elicited different movements of water in their immediate surroundings than occurred in the soil at large.