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Benefits of subcutaneous implantation of radiotransmitters in pocket gophers.

Advantages and disadvantages of competing techniques in radiotelemetry should be considered so that the best radio transmitter and method of attachment is chosen. Previous studies have shown high survivorship from intraperitoneal implants in pocket gophers (Zinnel and Tester, 1991; Benedix, 1994), yellow-bellied marmots (Marmota flaviventris, Van Vuren, 1989), American minks (Neovison vison), Franklin's ground squirrels (Spermophilus franklinii; Eagle et al., 1984), and other mammals (Koehler et al., 1987). Although intraperitoneal implants are successful in many mammalian species, other methods of attachment, such as subcutaneous implantation, maybe more reliable, feasible, or both, for certain species.

Radiotransmitters have been placed on collars around the neck (Andersen and MacMahon, 1981; Witmer et al., 1996), in cheekpouches (Artmann, 1967), and in peritoneal cavities (Zinnel and Tester, 1991; Benedix, 1994) of pocket gophers. The short necks of pocket gophers may cause radiocollars to slip off, whereas insertion of radiotransmitters into cheekpouches may affect foraging and can be removed by pocket gophers (Artmann, 1967). Surgical implantation in the peritoneal cavity is invasive, time consuming (often 20 min), and may cause additional stress or behavioral changes (Zinnel and Tester, 1991). Bandoli (1987) sutured radiotransmitters subcutaneously to the lateral aspect of the rump of pocket gophers. However, extended sedation for this ca. 45-min procedure may have caused unintentional stress. Cameron et al. (1988) took captured individuals to a screened enclosure where they placed radiotransmitters subcutaneously between scapulae. Individual pocket gophers were radiotracked in the field for 2 days after which animals were recaptured and radiotransmitters were removed. Because of the limitations of previous techniques for affixing radiotransmitters to subterranean mammals such as pocket gophers, we used a technique similar to Cameron et al. (1988). This technique allowed for quick implantation that could be carried out at the site of capture in [less than or equal to]10 min when performed by two people.

During 3 March 2007-10 February 2008, we inserted radio transmitters into 72 Ozark pocket gophers, Geomys bursarius ozarkensis, in Izard County, Arkansas. All surgical procedures followed guidelines of the American Society of Mammalogists (Gannon et al., 2007). We recorded mass of pocket gophers after capture (range = 41-274 g; n = 72) to determine appropriate size of radiotransmitter for each individual. We tested the technique of Cameron et al. (1988) by implanting radiotransmitters at the capture site and conducted long-term radiotracking using a Wildlife Materials TRX 1000S receiver (Wildlife Materials, Inc., Murphysboro, Illinois). We left radiotransmitters inside pocket gophers for [less than or equal to]9 months (range = 1-9 months), thereby greatly extending the 2-day period of Cameron et al. (1988). We returned each pocket gopher to its burrow within 1 h after implantation. We recaptured 22 individuals to examine any potential negative, long-term effects of subcutaneous implantation, including change in mass, infections, and restrained movements.

We classified female pocket gophers as adults if they had completed their first molt and had lost their pubic symphysis, and males were determined to be adults if they had completed their first molt and weighed [greater than or equal to]140 g (Wilks, 1963). We present data on adults by sex. Pocket gophers not meeting criteria to be considered as adults were classified as juveniles, and sexes in this age class were grouped together.

We implanted four sizes of radiotransmitters (SOPI-2038, SOPI-2070, and SOPI-2190, Wildlife Materials, Inc., Murphysboro, Illinois; PD-2H, Holohil Systems, Ltd., Carp, Ontario, Canada). Longevity of radiotransmitters was 3-9 months. The SOPI-2038 was 2.2 by 0.8 by 0.6 cm and weighed 1.8-2.2 g, the SOPI-2070 was 2.2 by 0.8 by 0.6 cm and weighed 2.0-3.0 g, the SOPI-2190 was 2.2 by 1.3 by 0.7 cm and weighed 4.0-6.0 g, and the PD-2H was 2.3 by 1.2 by 0.9 and weighed 3.9 g. Pocket gophers were implanted with the largest radiotransmitter possible, provided it was not >5% of the mass of the pocket gopher.

Of the 72 surgeries, 70 were successful. One radio transmitter was not retained after implantation in a female (188 g) likely due to insufficient closure of the incision. One old male (259 g) with worn teeth died during surgery, likely as a result of complications from the anesthesia.

Mean body mass for 20 adult males and 28 adult females was 206 g (SD = 47.9) and 159 g (SD = 15.8), respectively. Mean body mass of 24 juveniles was 94 g (SD = 30.4). Mean change in mass from implantation to recapture for adult males, adult females, and juveniles was 1.1% (SD = 11.9), -1.6% (SD = 9.0), 17.3% (SD = 18.8), respectively (Table 1). Mass of one juvenile increased from 44 to 61 g in 36 days; likely reflective of a normal rate of growth for a juvenile of that age.

No pocket gopher that was recaptured, including individuals that were recaptured [less than or equal to]325 days after having a radiotransmitter implanted, showed any sign of restrained movement, infection, or abnormal scarring from the surgery. Pocket gophers were captured and radiotransmitters were implanted in spring when food was abundant and the majority recaptured during drier, hotter months when food was less abundant, which resulted in some loss of mass (Table 1). Additional recaptures of females in winter suggested that losses in mass probably were due to pregnancy during the previous spring. Mean change in mass per day in the pocket gophers with radiotransmitters (0.09%; SD = 0.33) was similar to other pocket gophers recaptured that did not have implanted radiotransmitters (0.03%; SD = 0.13). A Wilcoxon rank-sum test did not reveal any significant difference between the two groups (P = 0.83).

Successful surgeries on juveniles, some as small as 41 g, showed potential applicability for use with other species. This is the first time subcutaneous radiotransmitters have been used during long-term studies of G. bursarius. Once radiotransmitters are placed subcutaneously, scientists can collect biological data on pocket gophers via radiotelemetry without intrusion into their closed burrow system (e.g., digging open the burrow to place a trap). Gathering data with subcutaneous radiotransmitters also might elucidate some biological questions currently unanswered, such as patterns and rates of dispersal (Busch et al., 2000).

We had comparable results (retention of radiotransmitters without infection) as those reported with subcutaneous implantations on other species of pocket gophers (Bandoli, 1987; Cameron et al., 1988). Subcutaneous implantation of radiotransmitters is a reliable procedure that can be successfully done under field conditions at the site of capture. The procedure described herein is the least intrusive and most appropriate for use in research with small mammals that are either fossorial or their morphology is not conducive to attachment of radiocollars. When completed in the field, this procedure minimizes time required for surgery and limits stress on the individual; thus, ensuring minimal alterations of behavior and physique. Furthermore, it is not a technical surgery and can be successfully done by field technicians without previous surgical training.

We thank A. Ryan for assistance and instruction concerning surgical procedures, I. Guenther for assistance with fieldwork and surgeries, D. Miller, M. Rush, R. H. and S. Smith, M. and K. Smith, and Y D. and N. Whitehurst for allowing us to conduct the study on their land. We thank B. Sasse for advice on this study, as well as the Arkansas State University Behavioral Ecology Lab, G. N. Cameron, and two anonymous reviewers for reviewing early drafts of the manuscript. Funding was provided by a state wildlife grant (SWG) from the Arkansas Game and Fish Commission. This research benefited from reassignment time granted to TSR from the Environmental Sciences program at Arkansas State University.

Submitted 26 February 2008. Accepted 28 August 2008. Associate Editor was Karen E. Francl.


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Department of Biological Sciences, Arkansas State University, P.O. Box 599, State University, AR 72467

* Correspondent.
TABLE 1--Initial mass and percentage change of 22 Ozark pocket
gophers (Geomys bursarius ozarkensis) at the time of implantation
of radiotransmitter and at the time of recapture, Izard County,

Sex Mass at Mass at Change in Days between
 implantation recapture mass captures
 (g) (g) (%)
Male 157 200 27.4 54
Male 165 178 7.8 47
Male 237 243 2.5 34
Male 220 212 -3.6 42
Male 257 245 -4.7 38
Male 257 244 -5.1 270
Male 274 253 -7.7 50
Male 248 228 -8.1 20
Female 149 179 20.1 57
Female 140 144 2.9 48
Female 146 150 2.7 53
Female 139 139 0 28
Female 174 168 -3.4 21
Female 161 155 -3.7 107
Female 173 160 -7.5 292
Female 155 143 -7.7 93
Female 168 155 -7.8 305
Female 170 151 -11.2 325
Juvenile 44 61 41.5 36
Juvenile 124 145 16.9 53
Juvenile 93 107 15.1 24
Juvenile 113 108 -4.4 50
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Author:Connior, Matthew B.; Risch, Thomas S.
Publication:Southwestern Naturalist
Article Type:Report
Geographic Code:1USA
Date:Jun 1, 2009
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