FACTORS AFFECTING THE NEST SITE SELECTION OF SMOOTH SOFTSHELL TURTLES (APALONE 
MUTICA)

Kirsten L. Brown, Michael A. Romano, and Susan T. Meiers 
Department of Biological Sciences, Western Illinois University, 1 University 
Circle, Macomb, IL 61455	

      Smooth softshell turtles (Apalone mutica) require several very specific 
habitat conditions to be met before the females will dig a nest and lay her 
eggs.  Preferred sites generally include sandy, open beaches that have very 
little disturbance from humans and predators, adequate temperature and exposure 
to light, and little to no vegetation present.  Softshell turtles were observed 
during the nesting and hatching seasons, mid-June to mid-October of 2006, at two 
locations along the Mississippi River near Hamilton, Illinois below lock and dam 
20.  Nests were identified as false, predated, or hatched based upon the 
presence and conditions of eggs.  Data were collected during weekly visits to 
the nest sites and included the temperature of all nests at the soil level and 
the temperature at the depth of six inches.  A square meter plot was measured 
around the center of each nest and the amount and type of vegetation recorded.  
The incline and clinometer were taken using a Suunto Tandem directly upstream of 
each nest.  The distance to vegetation lines created by the fluctuating river 
were taken from the permanent vegetation line to each and to the nest itself.  
We hypothesized that the softshell turtles would lay their eggs in sandy, open 
beaches, that have a slight slope, that have little predation or human 
disturbance, and no vegetation around the nests.  Also, previous research 
suggested that the temperature would be in a narrow range between 36-37oC.  A 
total of 582 nests were found, of which 12 hatched, 288 were false, and 282 were 
predated.  All hatched nests were found between August 25 and September 22, 
2006, with only one from the Missouri side beach.  Both soil and surface 
temperatures varied greatly over a broad range, with the most variation seen in 
false nests, followed by predated and then hatched.  Principle component 
analysis revealed three significant components corresponding to vegetation 
composition around the nests, effect of woods and its shading with surface 
temperature, and soil temperature and moisture respectively.  These components 
explained 82.7% of the variation in nest site selection of smooth softshell 
turtles.  Softshell turtles prefer to nest in sandy, open beaches that are 
slightly sloped, with little vegetation present around nest site which supported 
our hypothesis.  There was a broad temperature range that turtle nests were 
located for at both surface and soil temperatures.  Our hypothesis that turtles 
would prefer to nest on a site with little disturbance or predation did not 
prove to be based on the tremendous predation rate seen on both beaches. 

Key words: Apalone mutica, turtles, predation, temperature, soil