Comparative Abundances of Neotropical Small Mammals by Trap Height

Although effective methods for access to the canopy of tropical forests are available (Mori, 1984; Perry and Williams, 1981; Whitacre, 1981), trapping of small mammals in the forest canopy rarely has been attempted. Aside from Charles-Dominique et al. (1981), apparently no investigator has systematically or intensively used live traps in the canopy to capture small mammals, and data on most arboreal species is anecdotal. Several authors used traps at heights of 2-3 m to capture small mammals in the tropics (August, 1983; Fleming, 1972; Fonseca et al., 1982; O'Connell, 1979); however, it is not known if these understory samples are representative of the canopy fauna. During research near Manaus, Brazil (Lovejoy et al., 1986; Malcolm, 1988), I developed two simple and effective methods to trap small mammals in the forest canopy. Herein, I describe the two methods, and contrast species' abundances at trap heights of 15 m with those at trap heights of 2 m and ground level. In one method, two round, wooden poles approximately 0.9 m long and 3 cm in diameter were nailed together at one end to form a "V." A climber ascended a tree and once a suitable branch was reached, raised the traps and poles using a cord and pulley. The open ends of the "V" frame were nailed to opposite sides of the tree trunk and the closed end nailed or tied to a branch so that the "V" frame was horizontal. Traps were tied on top of the "V" frame, baited, and set (Fig. la). The pulley method required an upper frame with pulleys and a lower frame to which the traps were tied (Fig. Ib). To construct frames, we used either round poles of 3-cm diameter or square wood 2.5 by 2.5 cm. Poles were less expensive, but they split easily when nailed, rotted quickly, and were difficult to work with. A climber ascended, raised the upper frame using a cord and pulley, and nailed the upper frame into position. Care was taken to insure that the upper frame was level when in position, and that the pulleys were centered. One end of the cord was passed through the two pulleys on the upper frame and lowered to the ground. As the climber descended, a vertical gap was cut through the vegetation to allow passage of the lower frame. The baited and set traps were tied to the lower frame and raised into position by pulling the cord. When the lower frame abutted the upper frame, the cord was pulled tight and tied to the base of the tree. I used good-quality, 2-mm diameter parachute cord. For both methods, a 23by 8by 8-cm Sherman trap was secured using a piece of elastic on top of a 40by 14by 14-cm Tomahawk trap. I used two traps to reduce biases toward particular size classes of mammals. Both traps were baited with peanut butter and banana. Tomahawk traps also were baited with a cloth sac containing peanut butter and raisins, or in a few instances, prunes. Because insects rarely chewed through the cloth sac, it provided a long-term bait source. Traps were rebaited only after they contained an animal, or were otherwise sprung. To protect captured animals and traps from rain, Tomahawk traps were covered with a 30by 14-cm piece of clear plastic. Traps were examined each morning by use of binoculars. A small flag attached to a wire was fastened to the door of Sherman traps to indicate the position of the trap door (Fig. 1). Trees were climbed by use of a "foot-belt" (peconha). The method was fast, inexpensive, and did not damage trees; however, it was strenuous and only those trees with diameters at breast height of <40 cm could be climbed. Access to larger trees was possible only from neighboring trees or vines. Mean (+SD) diameter at breast height of trees climbed was 19 + 3.6 (range, 12-70) cm. Trees of some species could not be climbed during rain, or for some time thereafter. The first-described method was less expensive and simpler than the pulley method. Because placement of pulley stations above the fourth or fifth branch usually required removal of lower branches, traps could be placed at greater heights with the first-described method. However, trees had to be climbed more than once: to place traps, remove captures, and remove traps. The efficency of the method, therefore, was