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A comparison of trapping methodologies and grid size for small mammal research Moreau, France

Abstract

This study was designed to compare two distinct trapping systems in their ability to assess small mammal abundance, and to determine the optimal number of days to adequately sample populations. The hypothesis tested was that trapping for short periods of time throughout the field season would yield a more frequent regime of results, compared to trapping for longer periods two or three times a year. The study area was in Summerland, British Columbia, where deer mice (Peromyscus maniculatus), montane voles (Microtus montanus) and Great Basin pocket mice (Perognathus parvus) were livetrapped in grasslands on six 1-ha replicate grids from June to October 1997. Three of the grids were sampled for two consecutive nights, every three weeks, from June to October. The other three grids were trapped for ten consecutive nights in June, August and October. I suggest that trapping for short periods of time throughout the year or field season will give a better estimate of small mammal population dynamics. A minimum of two and maximum of four night trapping sessions throughout the field season is recommended. An additional objective of this study was to evaluate the differences between estimates of small mammal population densities from grids of different sizes, and to determine the optimal grid size in estimating abundance. The hypothesis tested was that 1-ha grids would be as precise as larger grids in assessing small mammal abundance. Study areas were located in Vernon, Penticton, Kamloops and Prince George, British Columbia. For Experiment A, deer mice and northwestern chipmunks (Tamias amoenus) were trapped on 5-ha grids from May to October 1991 and 1992, and population estimates from 1- and 2-ha grids within the 5-ha grids were compared. For Experiment B, Northwestern chipmunks were sampled on 1- and 9-ha grids from May to August, 1990 and 1991. One ha grids were found to be as precise as 2-and 5-ha grids for density estimation of deer mice and northwestern chipmunks. However, estimates from the 1-ha grids were higher than estimates from the 9-ha grids. Additional research should focus on using identical methodologies and trap type for both 1- and 9-ha grids.

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