12 J. Whitfield Gibbons and Raymond D. Semlitsch 



in a habitat. For example, a partial fence could lead to misinterpreta- 

 tions about the numbers of some species (e. g., K. subrubrum) that leave 

 or enter the aquatic area. Extrapolation errors would be less likely to 

 result from other species (e.g., S. odoratus) that appear to use the 

 perimeter in a more uniform manner (Table 3). 



Table 3. Directional disparities that could result from drift fence placement if 

 partial fencing is used in or around a habitat. Numbers are based on 

 total captures of semi-aquatic turtles in pitfall traps on either side of the 

 fence encircling Ellenton Bay, South Carolina, from 1975 to 1981. The 

 perimeter was arbitrarily partitioned into the four compass directions 

 for Chi-square contingency analysis. 



Species 



North 



East 



South 



West 



Chi-square 

 value 



Chelydra serpentina 



28 



34 



24 



24 



1.29 



Sternotherus odoratus 



43 



40 



52 



47 



0.98 



Pseudemys floridana 



33 



58 



44 



95 



10.86* 



Deirochelys reticularia 



101 



249 



119 



273 



60.34 ** 



Pseudemys scripta 



162 



365 



269 



228 



80.87 ** 



Kinosternon subrubrum 



801 



498 



204 



253 



305.48 ** 



TOTAL 



1168 



1244 



712 



920 



77.69 ** 



* P<.05 

 ** P< .01 



The temporal aspect is also critical, not only at the seasonal level 

 but in some instances on a daily basis (e. g. Hurlbert 1969; Gibbons 

 1970; Semlitsch et al. 1981). Long-term studies reveal that annual dis- 

 parities can be great enough to provide the potential for improper inter- 

 pretations if drift fences are used to sample habitats for short periods of 

 time (Gibbons and Bennett 1974: Table 4). 



Because of the factors discussed above, a well-constructed and 

 maintained drift fence with pitfall traps will be effective in capturing 

 most individuals of certain species in an area, and none of others. The 

 outstanding number of captures of A. talpoideum, as well as the high 

 recapture rate, suggest that the method is highly effective for this pond- 

 breeding, migratory species (Table 5). On the other hand, relatively few 

 adult black racers, Coluber constrictor (Table 2), have been captured in 

 pitfall traps on the SRP, although the species is very abundant in the 

 areas under study (Gibbons and Patterson 1978). Not surprisingly, these 

 and other large snakes easily escape from the traps. The same is true of 



