Comparison of captures between Sherman live traps and Museum Special kill traps.
Although there is abundant information regarding success of various types of traps in capturing small mammals, information often is contradictory and inconsistent among studies, and few studies have examined the same types of traps for comparative purposes (Lee, 1997). The Museum Special kill trap (Woodstream Corporation, Lititz, Pennsylvania) generally is considered to be more successful than any other type of trap. Two studies reported Museum Specials to be more successful in capturing small mammals than Sherman live traps (H. B. Sherman Traps, Tallahassee, Florida; Pendleton and Davison, 1982; Weiner and Smith, 1972); however, Sealander and James (1958) determined that Sherman traps were more successful than Museum Specials. Smith et al. (1971) noted that Museum Specials were more successful than Victor snap traps (Woodstream Corporation, Lititz, Pennsylvania), but Drickhamer and Mikesic (1993) reported the opposite; Perry et al. (1996) detected no difference between the two types of traps. Such contradictory results make it difficult to decide which type of trap will most effectively sample small mammals.
Despite inconsistencies in the literature regarding suitability of various types of traps, success in capturing small mammals is largely affected by timing and location of the research (Williams and Braun, 1983). It is difficult to make direct comparisons among traps because most published studies took place at different times and places, used different sampling protocols, and targeted different species. However, information obtained from previous projects has resulted in knowledge that can aid researchers in choosing the appropriate type of trap when studying small mammals. our research focused on comparing two types of traps at the same time and location. Specifically, objectives of our study were to compare total number of captures using Museum Specials and Sherman live traps, determine if sex, habitat, or species differ between types of traps, and determine if there was a difference in number of sprung-but-empty traps between types of traps.
MATERIALS AND METHODS--We trapped small mammals at Swan Lake National Wildlife Refuge near Sumner, Chartion County, Missouri. The refuge contains a diverse array of habitats ranging from a 1,214-ha permanent lake to managed wetlands and agricultural areas that produce various crops for wildlife. We selected five habitats that were most representative of the refuge (grassland, agricultural field, old field, cover-crop field, and bottomland forest). Following the procedure of Clark et al. (1998), four randomly placed replicate transects were established in each habitat. Each transect contained five trapping stations spaced 15 m apart in a linear fashion with two Sherman live traps (7.6 by 8.9 by 22.9 cm) and two Museum Specials (13.9 by 6.9 cm) for a total of 20 traps/ transect. Thus, each habitat had a total of 40 Sherman live traps and 40 Museum Specials/night. For a single trapping session, we simultaneously trapped all four transects for 4 consecutive nights in each of the five habitats, which totaled 320 trap nights/habitat. We sampled each of the five habitats four times; twice in summer 2002 and twice in summer 2003 for a total of 6,400 trap nights for the entire study. Before each trapping session, all traps were cleaned and inspected to ensure that they functioned properly. All traps were baited with peanut butter and rolled oats. All captured mammals were euthanized via thoracic compression, prepared as voucher specimens, and deposited in the Truman State University Mammal Collection. All procedures were conducted in accordance with Missouri Department of Conservation Wildlife Collector (permit 11728), Truman State University Animal Care and Use Committee (TSU 02-3), and guidelines of the American Society of Mammalogists (American Society of Mammalogists, 1998).
We directly compared total number of captures between Museum Specials and Sherman live traps with a randomized paired t-test. This test was used to compare overall total captures, differences in total captures among habitats, differences in total captures for each species, differences in total captures between sexes, and differences in number of sprung-but-empty traps. A sample distribution was created by automated random selections from the original paired data on trapping success. Random sampling was done 2,000 times and the actual data were then compared to the normal distribution created from the localized sample.
RESULTS--In 2 summers of trapping, we captured 1,078 small mammals representing 10 species in 6,400 trap nights. Trapping success for the entire study was 16.8%. Museum Specials generated 690 of the 1,078 total captures representing 64% of all captures. Sherman live traps generated 388 captures, representing 36% of total captures.
Results of the randomized t-test comparing total captures between Museum Specials and Sherman live traps show the Museum Specials captured significantly more small mammals than Sherman live traps (P = 0.002). There was no difference between sexes in total number of captures between Museum Specials and Sherman live traps (P = 0.342). There were 372 captures of males in Museum Specials, 198 captures of males in Sherman live traps, 330 captures of females in Museum Specials, and 200 captures of females in Sherman live traps. There were 828 sprung-but-empty Museum Specials and 110 sprung-but-empty Sherman live traps. The randomized t-test comparing number of sprung-but-empty traps indicate Museum Specials were sprung-but-empty significantly more than Sherman live traps (P < 0.001).
Results of the randomized t-test comparing differences in total captures within each habitat indicated that habitat was not a significant factor. Although Museum Specials captured more individuals in four of the five habitats sampled, particularly in the grassland, there was no significant difference between the two types of traps. When captures from 2002 are examined separately, however, significantly more small mammals were captured in Museum Specials in the grassland habitat (P < 0.001). The same is true of the cover-crop habitat. When a randomized t-test was conducted for captures in 2002, Museum Specials caught significantly more animals than Sherman live traps (P = 0.022) in cover-crop habitat.
Results of the randomized t-test indicate that significantly more western harvest mice (Reithrodontomys megalotis) and house mice (Mus musculus) were captured in Museum Specials than in Sherman live traps when captures across all habitats were combined. The North American deermouse (Peromyscus maniculatus) was captured in Museum Specials more often than in Sherman live traps; however, the difference was not significant. There was no significant difference in total number of captures for the white-footed
deermouse (Peromyscus leucopus), prairie vole (Microtus ochrogaster), meadow vole (Microtus pennsylvanicus), and northern short-tailed shrew (Blarina brevicauda), despite all species, except the white-footed deermouse, were captured in Museum Specials more often than in Sherman live traps. This analysis was not performed on the North American least shrew (Cryptotis parva), southeastern shrew (Sorex longirostris), and meadow jumping mouse (Zapus hudsonius) due to small samples.
DISCUSSION--Museum Specials captured significantly more individuals than the Sherman live trap and was also more successful at capturing a greater diversity of species (10) than the Sherman live trap (7). These results are consistent with previous studies conducted by Weiner and Smith (1972) and Pendleton and Davison (1982), which compared the two types of traps. Museum Specials captured the meadow jumping mouse, North American least shrew, and southeastern shrew, whereas the Sherman live trap did not.
The increased sensitivity of the Museum Specials presumably facilitates captures of smaller mammals such as Sorex and Cryptotis (West, 1985). The newest model of the Museum Special with a plastic treadle was used in our study, which has greater sensitivity than the older version with wooden treadles (West, 1985). increased sensitivity of the trap increases the chances of capturing an animal, yet also increases the incidences of sprung-but-empty traps. However, the cost is outweighed by the gain of capturing more animals. Despite the fact that Museum Specials were sprung-but-empty significantly more than Sherman live traps, Museum Specials captured more animals than the Sherman live traps.
Sex was not a factor in total captures between Museum Specials and Sherman live traps. There have been few studies that have examined sex as a factor in total captures for these two types of trap. one such study by Woodman et al. (1996) determined that there was no difference in capture of males or females between Victor Rat Traps (Woodstream Corporation, Lititz, Pennsylvania) and Sherman live traps. Results from our study indicate that Museum Specials and Sherman live traps are equally effective at capturing males and females and reduced gender bias when sampling small mammals.
Habitat was not a significant factor in total captures between the two types of traps. Although more individuals of two species were captured in Museum Specials, there was no evidence to suggest a particular habitat was a determining factor in total captures. Although more animals were caught in Museum Specials than Sherman live traps in grassland habitat, the difference was not statistically significant. Lack of significance was likely due to high variance in the data when results from 2002 and 2003 were combined. When captures were analyzed separately, significantly more small mammals were captured in Museum Specials in the grassland and the cover-crop habitats.
Significantly more individuals of the western harvest mouse and the house mouse were captured in Museum Specials than Sherman live traps. The western harvest mouse was captured primarily in grassland habitat and there might be a positive association between Museum Specials and total captures in grassland habitats. However, the house mouse was captured in the cover-crop habitat, which contained a significantly greater percentage of bare ground than grassland habitat (Eulinger, 2003). It is difficult to determine why these two species were more likely to be caught in Museum Specials, because there was no significant difference between total captures and the habitat itself. Also, these two species were captured in completely different habitats. it does provide evidence that the individual species might be the driving force in determining total capture success. Two sites in 2002 that captured significantly more animals in Museum Specials than Sherman live traps were grassland (which captured primarily western harvest mice) and cover-crop habitats (which primarily captured house mice). it appears that species are a stronger determining factor, because when data were pooled between 2002 and 2003, habitat was no longer a significant factor, but these two species remain as significant factors in total number of captures. Many researchers believe that Sherman live traps are biased toward capturing white-footed deermice, but our results indicate that Sherman live traps and Museum Specials were equally successful at capturing this species. instead, this study suggests greater total captures for the western harvest mouse and house mouse in Museum Specials.
Methods used for this study facilitated the use of a randomized paired t-test for analyzing the data generated. There were two traps of each type at every station; therefore, the data were paired and made for easy comparisons. Had there only been one of each type of trap at each station, validity of the results might have been compromised. if an animal was captured in one trap, only one other type of trap would remain to capture an animal. By default, the next animal would be captured in the remaining trap simply because there was no other choice. As a result, we would not know which trap was chosen first. Having four traps reduces the likelihood of an animal being caught in a trap solely because there were no other options. Although this method reduces potential bias in total number of captures, we were unable to determine which type of trap was chosen first if more than one animal were caught at a given station.
We have demonstrated how type of trap can influence results of a given study. Without Museum Specials, number of captures would have been much lower and some species such as the meadow jumping mouse, North American least shrew, and southeastern shrew would not have been detected. it is important, however, to understand that particular situations require the use of one type of trap over another. Sherman live traps are vital in conducting mark-recapture studies and also eliminate the potential risk of removing a species that is of conservation concern. Although our Museum Specials did capture more animals than Sherman live traps, certain types of data were necessarily lost including ectoparasites, karyotypes, and temperature-sensitive enzymes. Scavenging also can be problematic with the use of Museum Specials. Such considerations need to be addressed before determining which type of trap to use. For our purposes, using Sherman live traps in conjunction with Museum Specials facilitated the capture of every species of small mammal expected to inhabit Swan Lake National Wildlife Refuge.
Results of this study are specific to the place, time, and method used to capture these animals and conclusions generated from these results may not be applicable in every situation because of spatial and temporal variability. Although less emphasis can be placed on methods, choosing the correct method can greatly influence results of any study, particularly studies that involve sampling small mammals. Researchers can use this information and results from previous studies to make an educated decision on which type of trap to use to address a particular question of interest when trapping small mammals.
We thank Truman State University and the Missouri Department of Conservation for providing equipment and funding for this project, H. Doherty, the united States Fish and Wildlife Service, and personnel at Swan Lake National Wildlife Refuge for housing and access to the refuge, and M. Kelrick, G. Jones, A. Petry, S. Cooper, and J. Eulinger for assistance in the field and lab.
Submitted 16 February 2006. Accepted 6 October 2010. Associate Editor was Philip D. Sudman.
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KEVIN G. EULINGER * AND M. SCOTT BURT
Department of Biology, Truman State University, Kirksville, MO 63501 Present address of KGE: 310 Derek Drive, Hawk Point, MO 63349
* Correspondent: Kevin.Eulinger@mdc.mo.gov
TABLE 1--Total captures for Museum Special kill traps and Sherman live traps for each species of small mammal captured within each of five habitats sampled at Swan Lake National Wildlife Refuge near Sumner, Chariton County, Missouri. Results of randomized paired t-tests for species and habitats are indicated (* = P [less than or equal to] 0.05). Species Type of Grassland Agricultural Old trap field field Peromyscus Museum leucopus Special 0 79 0 Sherman live trap 0 108 0 Peromyscus Museum maniculatus Special 6 5 0 Sherman live trap 5 2 0 Reithrodontomys Museum megalotis Special 70 6 6 Sherman live trap 8 0 0 Microtus Museum ochrogaster Special 37 12 4 Sherman live trap 15 7 2 Microtus Museum pennsylvanicus Special 9 3 8 Sherman live trap 2 2 0 Mus musculus Museum Special 0 51 0 Sherman live trap 0 21 0 Blarina Museum brevicauda Special 1 3 0 Sherman live trap 1 1 0 Cryptotis parva Museum Special 4 0 0 Sherman live trap 0 0 0 Sorex longirostris Museum Special 2 0 0 Sherman live trap 0 0 0 Zapus hudsonius Museum Special 0 0 0 Sherman live trap 0 0 0 Total Museum Special 129 141 18 Sherman live trap 31 159 2 P-value (t-test among habitats) 0.112 0.706 0.095 Species Type of Cover-crop Bottomland Total trap field forest Peromyscus Museum leucopus Special 2 153 234 Sherman live trap 1 134 243 Peromyscus Museum maniculatus Special 97 0 108 Sherman live trap 47 0 54 Reithrodontomys Museum megalotis Special 6 1 89 Sherman live trap 0 0 8 Microtus Museum ochrogaster Special 42 7 102 Sherman live trap 16 3 43 Microtus Museum pennsylvanicus Special 11 2 33 Sherman live trap 3 0 7 Mus musculus Museum Special 61 0 112 Sherman live trap 9 1 31 Blarina Museum brevicauda Special 0 1 5 Sherman live trap 0 0 2 Cryptotis parva Museum Special 0 0 4 Sherman live trap 0 0 0 Sorex longirostris Museum Special 0 0 2 Sherman live trap 0 0 0 Zapus hudsonius Museum Special 1 0 1 Sherman live trap 0 0 0 Total Museum Special 220 164 672 Sherman live trap 76 138 406 P-value (t-test among habitats) 0.102 0.173 Species Type of P-value trap (t-test among species) Peromyscus Museum leucopus Special 0.769 Sherman live trap Peromyscus Museum maniculatus Special 0.085 Sherman live trap Reithrodontomys Museum megalotis Special 0.036 * Sherman live trap Microtus Museum ochrogaster Special 0.118 Sherman live trap Microtus Museum pennsylvanicus Special 0.102 Sherman live trap Mus musculus Museum Special 0.043 * Sherman live trap Blarina Museum brevicauda Special -- Sherman live trap Cryptotis parva Museum Special -- Sherman live trap Sorex longirostris Museum Special -- Sherman live trap Zapus hudsonius Museum Special -- Sherman live trap Total Museum Special Sherman live trap P-value (t-test among habitats)
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|Author:||Eulinger, Kevin G.; Burt, M. Scott|
|Date:||Jun 1, 2011|
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