2 J. Whitfield Gibbons and Raymond D. Semlitsch 



alongside the fence and buried flush with the ground at prescribed 

 intervals (Fig. 1 A). The intent is to intercept animals traveling overland 

 so that upon encountering the drift fence they turn left or right and 

 continue along the fence until they fall into a trap. 



Fences and traps used on the SRP have undergone a 13-year evolu- 

 tion of construction materials and design (Fig. 1B,C,D). The earliest drift 

 fences, constructed in 1968 of chicken wire, were intended only for cap- 

 ture of turtles moving overland. Twenty-liter (5-gallon) metal paint 

 buckets served as pitfall traps. From 1969 to 1971, hardware cloth (!4- 

 inch mesh) was used for fencing material. We have subsequently found 

 the most effective material to be 50 cm high aluminum flashing, of 

 which approximately 10 cm is placed below the surface of the ground. 

 This has the advantage of preventing small animals from passing under 

 or through the fence, or larger ones from using the mesh to climb over. 

 The flashing is also considered to be superior to various plastic fencing 

 materials used by other investigators (Storm and Pimentel 1954; Packer 

 1960; Husting 1965; Shoop 1974; Gill 1978; Wygoda 1979; Douglas 

 1979; Collins and Wilbur 1979) in that it is not easily torn or pushed 

 down by larger vertebrates such as turtles, alligators, feral pigs, or deer. 

 Furthermore, aluminum flashing does not rust or deteriorate with age 

 as do many other commonly used fence materials. 



Twenty-liter plastic buckets have proved to be the most effective 

 pitfall traps. These containers are relatively permanent, whereas metal 

 buckets begin to deteriorate within two years, making them less useful 

 for long-term studies. Although smaller volume traps (# 8 cans) have 

 been used effectively for certain species (Shoop 1965; Gill 1978; Douglas 

 1979), larger traps permit the capture of many species that can easily 

 escape from a shallow can. 



MAINTENANCE 



Once drift fences and pitfall traps have been constructed, mainten- 

 ance is required for continued effectiveness. Vegetation growing along- 

 side the fence should be mowed or cut to prevent animals from using it 

 to climb over, as well as to assure visibility in checking traps and fence 

 margins. Mowing chores can be reduced in some situations by placing a 

 heavy layer of sand alongside the fence, extending out 5-10 cm. 



Cracks or crevasses may develop along the fence or around buckets 

 following construction, particularly after heavy rainfalls. They should 

 be filled to prevent animals from using them as tunnels under the fence. 

 Pitfall traps often fill and overflow with water after heavy rains or from 

 rises in groundwater. Holes drilled in the bottom or sides will prevent 

 water accumulation in some instances, although on certain occasions 

 bailing may be necessary. 



