Mastozoología Neotropical / J. Neotrop. .; 9(1):85-89 ISSN 0327-9383 ©SAREM, 2002 Versión on-line ISSN 1666-0536

NOTA TÉCNICA - TECHNICAL NOTE

THE EFFECTIVENESS OF PITFALL TRAPS FOR SAMPLING SMALL IN THE AMAZON BASIN

Christine L. Hice and David J. Schmidly

Department of Biological Sciences, Texas Tech University, Lubbock, TX , USA 79409. Phone: (806)742-2121; Fax (806)742-2138; ;

ABSTRACT. Mammal communities in the Amazon Basin are diverse and should be as- sessed with a variety of trap types. Pitfall traps are infrequently used in surveys of Neotro- pical mammals, but capture a different subset of the small mammal community than do traditional trap types. Pitfall traps captured species generally thought to be rare, including Monodelphis adusta and melanops, at a higher proportion than traditional terres- trial traps. Moreover, pitfall traps captured more very young individuals of common species. This trapping technique is most effective during the rainy season, with virtually no captures recorded during the dry season, and should be used in conjunction with other trap types to fully assess mammal communities.

RESUMEN. La comunidad de mamíferos en la Cuenca Amazónica es diversa y debería ser evaluada con una variedad de tipos de trampas. Las trampas de caída no son usadas frecuentemente en estudios de mamíferos neotropicales, pese a que capturan un subgrupo diferente de la comunidad de pequeños mamíferos del que capturan las trampas tradiciona- les. Las trampas de caída capturan especies generalmente consideradas raras, incluyendo Monodelphis adusta y , en una proporción más grande que las trampas terrestres convencionales. Además, las trampas de caída capturan más individuos juveniles que las trampas tradicionales. Esta técnica de trampeo es más efectiva durante la estación de lluvias, con prácticamente ninguna captura durante la época seca, y debería ser usada en conjunto con otros tipos de trampas para evaluar en detalle las comunidades de mamí- feros.

Key words: pitfall traps, community assessment, trap comparison, Amazon Basin.

Palabras clave: trampas de caída, evaluación de comunidades, comparación de trampas, Cuenca Amazónica.

INTRODUCTION often results in an inaccurate assessment of the community (Edwards, 1952; Sealander and Lowland, Neotropical, rainforests harbor a di- James, 1958; MacLeod and Lethiecq, 1963; verse and structurally complex small mammal Wiener and Smith, 1972; Nellis et al., 1974; community. Components of this community Pizzimenti, 1979; Szaro et al., 1988; McComb inhabit a variety of niches ranging from semi- et al., 1991; Laurance, 1992; Kalko and fossorial to arboreal. This diversity of life his- Handley, 1993; Woodman et al., 1996). This tories makes it difficult to accurately survey bias can be corrected by using trapping tech- the mammalian fauna of an area (Voss and niques that adequately assess each component Emmons, 1996). Moreover, failure to use a of the small mammal community. variety of trap types and trapping techniques Pitfall traps have not been used extensively 86 Mastozoología Neotropical / J. Neotrop. Mammal.; 9(1):85-89 Mastozoología Neotropical, 2002

to capture small mammals in Neotropical habi- 2945 mm per year, with a slightly drier season from tats. However, in North America pitfall traps June to September (Johnson, 1976). The elevation have been successfully used to capture semi- of the station ranges from 110 m to 180 m above fossorial mammals, such as shrews (Prince, sea level. Thirteen pitfall traplines were established in con- 1941; Moore, 1949; Peterson and Symansky, junction with other capture methods in three types 1963; Brown, 1967; Wharton, 1968; Buckner, of primary forest and five ages of secondary growth 1969; Hoffman et al., 1969; Pucek, 1969; Layne forest to assess small mammal communities. Pitfall and Shoop, 1971; Briese and Smith, 1974; traplines consisted of eleven 20 L buckets buried Mengak and Guynn, 1987; Pagels, 1987; flush to the ground and placed 5 m apart under a McComb et al., 1991; Handley and Kalko, continuous 50 m drift fence made of plastic held 1993; Kalko and Handley, 1993). Moreover, it erect by stakes (Voss and Emmons, 1996). Holes has been demonstrated that pitfall traps sample were drilled in the bottom of each bucket to allow a different subset of the small mammal com- accumulated rainwater to drain. Instead, the holes allowed groundwater to enter. Each trapline took munity than do other, more traditional, trap- about 2 days to construct: one day to dig holes and ping methods (MacLeod and Lethiecq, 1963; bury the buckets and one day to put up the drift Briese and Smith, 1974; Nellis et al., 1974; fence. Materials to build the trapline were readily Williams and Braun, 1983; Mengak and Guynn, available locally with the exception of a staple gun 1987; Szaro et al., 1988; McComb et al., 1991; and staples to secure the plastic fence to the stakes. Laurance, 1992; Handley and Kalko, 1993; Traps were assessed for 10 consecutive nights and Kalko and Handley, 1993). checked each morning at dawn. No bait was used Whereas shrews are not a component of small nor was liquid intentionally introduced into the mammal communities in the Amazon Basin, it buckets ( Care and Use Committee, 1998). Specimens collected are deposited at the Museum has been suggested that other semi-fossorial of Texas Tech University, Lubbock, Texas, and the mammals, such as short-tailed opossums Museo de Historia Natural de la Universidad (Monodelphis), may be captured in the same Nacional Mayor de San Marcos, Lima, Peru. Pre- manner (Voss and Emmons, 1996). No studies served tissues (frozen) include heart, kidney, liver, have been conducted in Amazonia to deter- spleen, lung, and muscle, and are deposited at the mine if pitfall traps capture a different subset Museum of Texas Tech University. of the small mammal community than do other trap types. If they do, the inclusion of pitfall RESULTS AND DISCUSSION traps in the trapping regime could provide a more accurate assessment of the community. In total, 100,637 trap nights were compiled Herein, we summarize the results of the first yielding 1,030 captures and a capture rate of extensive use of pitfall traps in Amazonia. 0.97%. Of these, 59 individuals representing Detailed comparisons with other trap types will 12 mammalian species were captured in 2,530 be presented elsewhere. pitfall trap nights (Table 1). The overall pitfall capture rate was 2.33%, although it varied MATERIALS AND METHODS monthly (Table 2). Seasonal effects on cap- ture rate were pronounced, with one capture Small mammals were collected by one of us (CLH) (0.14%) during the 4-month dry season (June during 18 months (August 1997 to December 1998) to September) and up to a 4.55% monthly near Iquitos, Peru, for an ecological research project. capture rate during the rainy season (average Research was conducted at the Estación Biológica rainy season capture rate = 3.16%). The mass Allpahuayo (S3°58'; W73°25'), a 3000-hectare field of mammals captured in pitfall traps varied station operated by the Instituto de Investigaciones de la Amazonía Peruana (IIAP), 25 km south of from 2 to 93 g. However, only 6 individuals Iquitos, Department of Loreto, in northeastern Peru. with a mass >50 g were captured in pitfall The climate is tropical with a mean annual tempera- traps. ture of 26°C; the highest average monthly tempera- Pitfall traps demonstrated a higher capture ture (31°C) occurs in November and the lowest rate (2.29%) than did other trap types, includ- (22°C) in July (Salati, 1985). Average rainfall is ing snap-type Victor rat traps (1.08%), Toma- NOTA TÉCNICA - TECHNICAL NOTE 87

Table 1 List of number of individuals of each species captured in pitfall traps from August 1997 to December 1998.

Species Number Captured Marmosops noctivagus 4 Marmosops bishopi 3 Monodelphis adusta 5 spinosus 2 15 bicolor 5 1 microtus 7 megacephalus 1 Oryzomys yunganus 5 Scolomys melanops 11 Total 59

Table 2 Number of trapnights, captures recorded, and capture rate for each month during the study period.

Month Trapnights Captures Capture Rate (%) August-1997 22 1 4.55 September-1997 55 0 0 October-1997 0 0 na November-1997 550 19 4.32 December-1997 220 7 3.18 January-1998 0 0 na February-1998 0 0 na March-1998 330 9 2.73 April-1998 0 0 na May-1998 220 10 4.55 June-1998 121 0 0 July-1998 330 0 0 August-1998 99 0 0 September-1998 110 0 0 October-1998 319 7 3.13 November-1998 275 6 1.09 Total 2530 59 2.33 88 Mastozoología Neotropical / J. Neotrop. Mammal.; 9(1):85-89 Mastozoología Neotropical, 2002

hawk live-traps (0.92%), and Sherman live- permission to conduct research at the biological station; traps (0.45%). However, pitfall traps were to- thanks also to Víctor Pacheco for translating the abstract to Spanish. INRENA supplied necessary collecting per- tally ineffective during the dry season. A con- mits (#21-98-INRENA-DGANPFS-DCFS). This work was current depression in overall capture rate was supported in part by research grant AI-39800 from the not observed for other trap types. However, National Institutes of Health. genera (such as Neacomys) usually captured in pitfall traps and other trap types were less fre- LITERATURE CITED quently captured in non-pitfall traps during the dry season. This suggests that small species ANIMAL CARE AND USE COMMITTEE. 1998. taken more frequently in pitfall traps may ex- Guidelines for the capture, handling, and care of mammals as approved by the American Society of perience lower abundance or lower activity Mammalogists. Journal of Mammalogy, 79:1416- level during these months. In 1998, the rainy 1431. season began almost one month late (October BRIESE, L.A. and M.H. SMITH. 1974. Seasonal 26), which was reflected by the capture rate of abundance and movement of nine species of small mammals. Journal of Mammalogy, 55:615-629. pitfall traps (all seven captures in October 1998 BROWN, L.N. 1967. Ecological distribution of six species were on or after this date). Incidentally, this of shrews in the central Rocky Mountains. Journal of was also true of the herpetofauna of the area. Mammalogy, 48:617-623. Pitfall traps did not capture any unique spe- BUCKNER, C.H. 1969. Some aspects of the population ecology of the common shrew, Sorex araneus, near cies when compared to other trap types. How- Oxford, England. Journal of Mammalogy, 50:326- ever, they did capture a different subset of the 332. small mammal community, including 5 of 6 EDWARDS, R.Y. 1952. How efficient are snap traps in Monodelphis adusta and 11 of 24 Scolomys taking small mammals? Journal of Mammalogy, 33:497-498. melanops. Moreover, pitfall traps captured HANDLEY, C.O., JR. and E.K.V. KALKO. 1993. A short more younger/smaller individuals than did other history of pitfall trapping in America, with a review trap types, capturing mammals as small as 2 g. of methods currently used for small mammals. This may be important in population and de- Virginia Journal of Science, 44:19-26. HOFFMAN, R.S.; P.L. WRIGHT, and F.E. NEWBY. mography studies, since very young individu- 1969. The distribution of some mammals in Montana. als often are not captured in other trap types. I. Mammals other than bats. Journal of Mammalogy, Larger small mammals (over 50 g) were infre- 50:579-604. quently captured in pitfall traps, probably be- JOHNSON, A.M. 1976. The climate of Peru, Bolivia, and Ecuador. Pp. 147-210. In: Climates of Central cause they can escape. Consequently, small and South America. World Survey of Climatology mammals such as Proechimys, Oryzomys, Phi- Vol. 12 (Schwerdtfeger, W., ed.). Elsevier Scientific, lander, Metachirus, and Marmosops were not Amsterdam. frequently captured in pitfall traps and need to KALKO, E.K.V. and C.O. HANDLEY, JR. 1993. Comparative studies of small mammal populations be sampled with a different trap type (e.g. with transects of snap traps and pitfall arrays in Victor, Sherman, Tomahawk). Southwest Virginia. Virginia Journal of Science, 44:3- In conclusion, it is important to use a large 18. variety of trap types to assess small mammal LAURANCE, W.F. 1992. Abundance estimates of small mammals in Australian tropical rainforest: a communities in the Amazon Basin because of comparison of four trapping methods. Wildlife the high level of diversity present there. If pitfall Research, 19:651-655. traps are not used, the abundance of certain LAYNE, J.N. and C.R. SHOOP. 1971. Records of the species will be underestimated or the species water shrew (Sorex palustris) and smokey shrew (Sorex fumeus) from Rhode Island. Journal of could be missed entirely. The use of pitfall Mammalogy, 52:215. traps complements other trap types and should MACLEOD, C.F. and J.L. LETHIECQ. 1963. A be included in the design of comprehensive comparison of two trapping procedures for Sorex mammalian surveys in Amazonia. cinereus. Journal of Mammalogy, 44:277-278. MCCOMB, W.C.; R.G. ANTHONY, and K. MCGARIGAL. 1991. Differential vulnerability of ACKNOWLEDGEMENTS small mammals and amphibians to two trap types and two bait types in Pacific Northwest forests. We thank Dr. Victor Montrueil with the Instituto de Northwest Science, 65:109-115. Investigaciones de la Amazonia Peruana for granting MENGAK, M.T. and D.C. GUYNN, JR. 1987. Pitfall NOTA TÉCNICA - TECHNICAL NOTE 89

and snap traps for sampling small mammals and SEALANDER, J.A. and D. JAMES. 1958. Relative herpetofauna. American Midland Naturalist, 118:284- efficiency of different small mammal traps. Journal 288. of Mammalogy, 39:215-223. MOORE, J.C. 1949. Notes on the shrew, Sorex cinereus, SZARO, R.C.; L. SIMONS, and S.C. BELFIT. 1988. in the southern Appalachians. Ecology, 30:234-237. Comparative effectiveness of pitfalls and live-traps NELLIS, C.H.; C.J. TERRY, and R.D. TABER. 1974. A in measuring small mammal community structure. conical pitfall trap for small mammals. Northwest Pp. 282-288. In: Management of amphibians, reptiles, Science, 48:102-104. and small mammals in North America (Szaro, R.C.; PAGELS, J.F. 1987. The pygmy shrew, rock shrew and K.E. Severson, and D.R. Patton, technical mater shrew: Virginia’s rarest shrews (Mammalia: coordinators). USDA Forest Service General Technical Soricidae). Virginia Journal of Science, 38:364-368. Report RM-166. PETERSON, R.S. and A. SYMANSY. 1963. First record VOSS, R.S. and L.H. EMMONS. 1996. Mammalian of the Gaspé shrew from New Brunswick. Journal of diversity in Neotropical lowland rainforests: a Mammalogy, 44:278-279. preliminary assessment. Bulletin of the American PIZZIMENTI, J.J. 1979. The relative effectiveness of three Museum of Natural History, 230:1-115. types of traps for small mammals in some Peruvian WHARTON, C.H. 1968. First records of Microsorex hoyi communities. Acta Theriologica, 24:351-361. and Sorex cinereus from Georgia. Journal of PRINCE, L.A. 1941. Water traps capture the pygmy shrew Mammalogy, 49:158. (Microsorex hoyi) in abundance. Canadian Field WIENER, J.G. and M.H. SMITH. 1972. Relative Naturalist, 55:72. efficiencies of four small mammal traps. Journal of PUCEK, Z. 1969. Trap response and estimation of Mammalogy, 53:868-873. numbers of shrews in removal caches. Acta WILLIAMS, D.F. and S.E. BRAUN. 1983. Comparison Theriologica, 14:403-426. of pitfall and conventional traps for sampling small SALATI, E. 1985. The climatology and hydrology of mammal populations. Journal of Wildlife Amazonia. Pp. 18-48. In: Amazonia. Key Management, 47:841-845. Environments Series ( Prance, G.T. and T.E. Lovejoy, WOODMAN, N.; R.M. TIMM, N.A. SLADE, and T.J. eds.). Pergamon Press, Oxford, United Kingdom. DOONAN. 1996. Comparisons of traps and baits for censusing small mammals in Neotropical lowlands. Journal of Mammalogy, 77:274-281.