4 J. Whitfield Gibbons and Raymond D. Semlitsch 



In addition to the hazards of too much water, traps must be 

 checked at frequent intervals to avoid desiccation, predation, and other 

 problems that can arise. In sampling amphibians, desiccation can be 

 avoided at most times of the year by a daily checking schedule. A more 

 frequent checking routine, or use of wet sponges in the bottom of traps, 

 can prevent desiccation or lessen heat stress during summer. Reptiles 

 and mammals are typically more resistant to desiccation and can remain 

 in pitfall traps for longer periods of time than amphibians. 



The probability of predation on animals in pitfall traps increases 

 the longer they go unchecked, hence checking at several day intervals 

 would not be desirable in most instances. Daily checking is recom- 

 mended under most circumstances, although more frequent checking 

 (i.e., two or three times a day) may be necessary during mass migration 

 of amphibians from breeding ponds, or when prolonged disruption of 

 the animals' activity is detrimental. Use of an electric wire system 

 designed to safeguard each pitfall trap is effective in deterring most 

 mammalian predators except shrews (C. R. Shoop, pers. comm.). 



TIME, COST, AND EFFORT TO CONDUCT A STUDY 

 Drift fences with pitfall traps yield a wealth of biological informa- 

 tion, often providing ecological perspectives that could be obtained in 

 no other manner. However, the cost in labor and materials can be great. 

 The time investment in an effective drift fence operation can be parti- 

 tioned into construction, maintenance, and operation (Table 1). Initial 

 cost of construction is high, both for materials and in time required for 

 installation. After construction, the cost for materials is small; however, 

 the time investment can become onerous if the traps are checked in an 

 effective manner, such as daily (Table 1). 



Although the time and effort put into drift fence construction, 

 maintenance, and operation are high, data accumulation is often super- 

 ior to any other form of collecting for a wide variety of terrestrial anim- 

 als, particularly amphibians (Fig. 2; Table 2). The technique is highly 

 cost effective once the critical investment level has been reached. This is 

 especially true for long-term ecological studies where continuous daily 

 hand sampling is impractical. 



INTERPRETATION OF RESULTS 

 Drift fences with pitfall traps yield large amounts of data on 

 numbers (often total population sizes), seasonality, migration patterns, 

 diversity, and distribution patterns of many animals (see references in 

 Introduction; Table 2). Some species are collected in high numbers that 

 closely represent the actual population size, whereas the proportional 

 capture of others is below that of their actual abundance. However, as 



