Aspects of the Niche of the Common Snapping Turtle, 'Chelydra Serpentina Serpentina', in Iowa

Abstract

The problem. Large gaps exist in knowledge of the niche of Chelydra s. serpentina in Iowa. Much of the literature is anecdotal and some is contradictory. Aspects of this turtle's niche investigated were growth and maturity, habitat preference, daily and seasonal activity cycles, response to a severe drought, population structure, home ranges, and homing ability. Procedure. Turtles collected statewide and preserved were used in growth maturity studies. A population of snapping turtles was monitored to provide information on the other aspects mentioned. Findings. Growth is accomplished in an activity period of 204 days and a 145 day feeding period with growth beginning in late May. Most males are mature by the end of their fifth year at plastral lengths of 149-155 mm while most females are not mature until their seventh year at plastral lengths greater than 162 mm. Growth slows with maturity. Activity is greater at night. During severe drought snapping turtles are less active, burrow in mud or terrestrially, and move in association with rainy periods. They showed evidence of home ranges, homing ability, and most long distance movements were made in fall or spring. Apparently there is a sex ratio shift as snapping turtles mature. Conclusions. Males mature before females. This late maturity of females may decrease the ability of snapping turtle populations to recover from exploitation by man. Snapping turtle behavior during drought presumably results in decreased mortality due to heat and desiccation. Snapping turtles appear to have home ranges that are large (1.33 ha), temporary (perhaps lasting a season), and overlapping implying that they are not strongly defended against other snapping turtles. They apparently have some homing ability. Recommendations. More females need to be collected between ages five and eight, because further work on the apparent sex ratio shift is necessary. Also further study involvinq radio-telemetry, especially on the affect of season and sex on activity, would prove fruitful.