Gopher Populations Research Articles

Experimental translocation for restoration of an ecosystem engineer

The longleaf pine (Pinus palustris Mill.) savanna ecosystem in North America has declined by 97% from its historic range and its restoration is a conservation priority. The southeastern pocket gopher (Geomys pinetis), an ecosystem engineer in longleaf pine savannas, is absent from most of its historic range. Translocation of pocket gophers may be needed to reestablish ecosystem services of restored longleaf savannas. To determine translocation feasibility, we quantified survival, site fidelity, and homing of pocket gophers translocated using soft releases (with a starter burrow system; n = 13), hard releases (without a starter burrow system; n = 17), or released into their own burrows (control; n = 10). Naïve survival was 46 and 35% for soft‐ and hard‐released individuals, respectively, and 80% for controls. Most mortalities of translocated individuals (75.0%) occurred within 12 days. Including all radiotagged pocket gophers, daily survival of soft‐released animals ( = 0.990) was intermediate between hard‐released ( = 0.986) and controls ( = 0.993), and only hard‐released was lower than controls. Using only individuals that survived greater than 14 days, we found no difference in daily survival. Site fidelity was low, with 70% of translocated pocket gophers making aboveground movements away from release point. However, soft‐released individuals stayed at the release point three times longer than hard‐released animals. No pocket gopher exhibited homing. Our results suggest translocation has potential for establishing pocket gopher populations into restored longleaf pine savannas and that mitigating mortality during establishment will increase the likelihood of success.

Effect of the Current Climate Warming on the Terms of Key Phenological Stages in the Population of <i>Spermophilus pygmaeus</i> Pallas, 1778 (Rodentia, Mammalia) in the Ergenin Upland Territory

Журнал принимает на русском и английском языках статьи, представляющие результаты научных исследований в различных областях теоретической и прикладной экологии. Приоритет отдается научным статьям, основанным на явно сформулированных гипотезах.

Temporal and spatial dynamics of competitive parapatry in chewing lice.

We synthesize observations from 1979 to 2016 of a contact zone involving two subspecies of pocket gophers (Thomomys bottae connectens and T. b. opulentus) and their respective chewing lice (Geomydoecus aurei and G. centralis) along the Río Grande Valley in New Mexico, U.S.A., to test predictions about the dynamics of the zone. Historically, the natural flood cycle of the Rio Grande prevented contact between the two subspecies of pocket gophers. Flood control measures completed in the 1930s permitted contact, thus establishing the hybrid zone between the pocket gophers and the contact zone between their lice (without hybridization). Since that time, the pocket gopher hybrid zone has stabilized, whereas the northern chewing louse species has replaced the southern louse species at a consistent rate of ~150 m/year. The 0.2–0.8 width of the replacement zone has remained constant, reflecting the constant rate of chewing louse species turnover on a single gopher and within a local pocket gopher population. In contrast, the full width of the replacement zone (northernmost G. centralis to southernmost G. aurei) has increased annually. By employing a variety of metrics of the species replacement zone, we are better able to understand the dynamics of interactions between and among the chewing lice and their pocket gopher hosts. This research provides an opportunity to observe active species replacement and resulting distributional shifts in a parasitic organism in its natural setting.

A population model of the impact of a rodenticide containing strychnine on Great Basin Gophersnakes (Pituophis catenifer deserticola).

Strychnine is a neurotoxin and an active ingredient in some rodenticides which are placed in burrows to suppress pocket gopher (Thomomys talpoides) populations in range and crop land in western North America. The population level impact was modelled of the use of strychnine-based rodenticides on a non-target snake species, the Great Basin Gophersnake (Pituophis catenifer deserticola), which is a predator of pocket gopher and a Species at Risk in Canada. Using information on population density, demographics, and movement and habitat suitability for the Gophersnake living in an agricultural valley in BC, Canada, we estimated the impact of the poisoning of adult snakes on the long-term population size. To determine the area where Gophersnakes could be exposed to strychnine, we used vendor records of a rodenticide, and quantified the landcover areas of orchards and vineyards where the compound was most commonly applied. GIS analysis determined the areas of overlap between those agricultural lands and suitable habitats used by Gophersnakes. Stage-based population matrix models revealed that in a low density (0.1/ha) population scenario, a diet of one pocket gopher per year wherein 10% of them carried enough strychnine to kill an adult snake could cause the loss of 2 females annually from the population and this would reduce the population by 35.3% in 25years. Under the same dietary exposure, up to 35 females could die per year in a high density (0.4/ha) population which would result in a loss of 50% of adults in 25years.

Burrow fumigation versus trapping for pocket gopher (Thomomys spp.) management: a comparison of efficacy and cost effectiveness

Context Pocket gophers (Geomyidae) cause extensive damage to many crops throughout western North America. A variety of methods are available to manage these populations, but data are often lacking on their efficacy and especially their cost effectiveness. Additionally, little peer-reviewed data are available that compare multiple methods simultaneously. Aims We tested aluminum phosphide and pressurised exhaust using the Pressurised Exhaust Rodent Controller (PERC) as burrow fumigants, and compared them to trapping to determine which approach was most efficacious and cost effective. Methods We assessed the efficacy of aluminum phosphide, the PERC machine, and trapping through the use of the open-hole monitoring method after single and multiple treatments over multiple years. We determined material and labour costs for each treatment type and amortised this cost over 1250 days of application to determine which treatment type was most cost effective. Key results Aluminum phosphide had the shortest time for application, but we were able to make far more applications per day using the PERC machine, given our ability to treat multiple burrow systems at once with this machine. Trapping and aluminum phosphide were more efficacious than was the PERC machine. When costs were amortised over time, trapping was the most cost-effective approach even with longer application times, given high efficacy. Multiple treatment applications were needed to maximise the efficacy of management programs. Conclusions For small-scale management efforts, aluminum phosphide was a cost-effective and efficacious option. For a greater number of treatments, trapping was the most successful and cost effective. However, a modest increase in efficacy could make the PERC machine a preferred tool as well. We also stress that regardless of the management approach, multiple treatment applications will generally be needed to manage pocket gopher populations. Implications The present study provides growers with information needed to determine efficient and cost-effective methods for managing pocket gophers. This information can be used to craft an integrated pest-management approach to manage damaging pocket gopher populations.

Gopherbusters? A Review of the Candidacy of Barn Owls as the Ultimate Natural Pest Control Option

Author(s): Kross, Sara M.; Baldwin, Roger A. | Abstract: While many raptor species consume rodent pests, the behaviors and habits of barn owls make them particularly suitable candidates for consideration as a viable pest control strategy. As a cavity-nesting species, barn owls will readily nest in man-made structures including nest boxes. Barn owls are also less territorial than many other raptor species and will tolerate other pairs nesting nearby if prey is abundant. Barn owls preferentially consume rodents including voles (Microtus spp.) and pocket gophers (Thomomys spp.) in habitats where they occur, but will also switch to more abundant prey so they may be able to sustain populations even if preferred prey numbers fall. These life-history traits allow for people to inflate barn owl populations in target areas, and this has been a factor in the widespread popularity of encouraging barn owls to nest in agricultural areas to provide natural pest control of small nocturnal vertebrate pests. However, the ability of barn owls to control rodent pests has only been formally tested in Malaysian rice and palm oil agriculture, and whether barn owls are capable of controlling rodent pests to economically acceptable levels in areas such as California is as yet unknown. We extracted and combined data from field studies of barn owl nesting behavior and diet in California vineyards to predict that annually, a pair of nesting barn owls and their progeny will consume 97.85 kg of prey. We predicted that an average barn owl nest in a California vineyard will therefore consume 843 pocket gophers, 578 voles, and 1,540 other prey items, most of which are mice. At these values, a barn owl population density of one nest/10 ha may be able to offset the annual productivity of an average population of pocket gophers, but even the highest barn owl densities of one nest/2 ha would be unable to control pocket gopher populations at maximum densities and reproductive rates. While valuable for making initial predictions of the ability of owls to control small rodent pests, our prediction methods are crude, and accurately assessing the capability of barn owls to control rodent pests will require more field data and more sophisticated modeling techniques.

Use of External Characteristics for Rapid Identification of Gender of Pocket Gophers

Abstract. Pocket gophers are of great importance both for their function in ecological systems and for their impact on anthropogenic environments. Managing pocket gopher populations requires a fundamental understanding of population demographics, specifically sex ratios; yet quick and reliable techniques for visually identifying gender of pocket gophers are lacking. We developed a visual identification method based on external characteristics of genitalia and mammae that allows for rapid, yet correct assessment of gender in pocket gophers. This approach was particularly accurate (>99%) for visual identifications in the field. Our approach was also accurate (>98%) for frozen specimens, although care must be taken when identifying gender of frozen, immature pocket gophers. Although our results pertain specifically to Thomomys talpoides and Thomomys bottae, we believe that our methodology can be broadly applied to additional pocket gopher species.

Refinement of a trapping method increases its utility for pocket gopher management

Trapping is a useful and effective tool for managing detrimental pocket gopher populations, and methods to increase its effectiveness are in high demand. The Gophinator trap previously proved more efficient than the Macabee trap, primarily because of its ability to capture larger pocket gophers. However, the Macabee is still widely used given large stockpiles of these traps by land managers and pest control operators. The addition of a cable restraint to the front of the Macabee may be sufficient to keep larger individuals from escaping capture, thereby allowing trappers to more effectively use this common trap. Human scent may also impact trap success by deterring pocket gophers from entering trap sets. Therefore, we tested the capture efficiency and visitation rate of trap sets when using both Gophinator and modified Macabee traps to determine the potential utility of these trap designs. We compared these results to a previous investigation to better define the potential usefulness of the cable restraint on the Macabee. We also tested the impact of human scent on capture efficiency and visitation rate to determine the potential relevance of eliminating human scent from trap sets. Gender and weight of captured individuals were used to determine their potential impacts on capture efficiency and visitation rate. We found that the Gophinator was a more effective trap than the modified Macabee because of its ability to capture larger pocket gophers more efficiently. However, the modification did appear to increase capture efficiency of larger individuals when compared to the standard Macabee, suggesting that this modification could be used to increase the effectiveness of trapping programs when Gophinator traps are unavailable. Glove use had no impact on capture efficiency or visitation rate.

Understanding Trapping as a Tool to Manage Pocket Gophers

The pocket gopher is one of the most damaging vertebrate pests in California and throughout much of North American. Many options are available for managing pocket gophers including the use of rodenticides, burrow fumigation, and trapping. Trapping can be time consuming and labor intensive in some situations, but the efficacy of this approach can often offset these negative attributes. As such, we have engaged in several research projects over the last 5 years to increase the utility and effectiveness of trapping as part of an Integrated Pest Management (IPM) program for pocket gopher control. When comparing traps, we found that the Gophinator trap was a more effective trap than the Macabee, particularly when trapping larger pocket gophers. There does not appear to be a substantial benefit to covering trap-sets in most situations, but if trapping when temperatures are high, covering trap-sets may provide a slight increase in capture efficiency. If covering trap-sets, utilizing peanut butter might provide a slight increase in capture success; attractants provide no benefit if using uncovered trap-sets. Trapping was a highly effective technique for managing pocket gopher populations in crop fields. Furthermore, only 3 days were required for novice trappers to become efficient at capturing pocket gophers, although additional experience does increase the rate of capture. Collectively, these results validate the importance of including trapping in an IPM program, and should benefit all individuals who utilize trapping for managing pocket gopher populations.

Pocket Gophers and the Invasion and Restoration of Native Bunchgrass Communities

More than 7 million hectares of California native plant communities are now dominated by exotic annual species, a biological invasion that has made native bunchgrass ecosystems in this region one of the most endangered ecosystems in North America. Many land use and environmental factors have contributed to the conversion of bunchgrass areas to annual grassland, but the role of gopher disturbance remains understudied. Here I report observational evidence that suggests gopher foraging is nonrandomly concentrated in the open spaces between clumps of bunchgrass and as a result may inhibit the recruitment of bunchgrass into these areas. Understanding patterns of direct gopher impact and coincident soil disturbance in bunchgrass versus annual grassland is important for successful restoration of bunchgrass habitats. While the prospect of excluding gophers is daunting, even short-term reductions in gopher populations would help to promote a restored community structure with a mature native bunchgrass and annual forb association.

Live Trap for Pocket Gophers

Abstract We presented a new trap for pocket gophers and compared its effectiveness with the Baker and Williams live trap. Our box trap readily captured juveniles ≥44 g and adults ≤294 g. We had ≤50% capture success. In general, capture success was similar to the Baker and Williams live trap. However, analyses suggested that our trap was superior in some aspects, e.g., capture of heavier pocket gophers and males. Our trap was user friendly and could be employed to equally capture all portions of a population of pocket gophers.

Efficacy of Cholecalciferol Baits for Pocket Gopher Control and Possible Effects on Non-Target Rodents in Pacific Northwest Forests

Author(s): Rizor, Suzanne E.; Arjo, Wendy M.; Bulkin, Stephan; Nolte, Dale L. | Abstract: Population reduction measures need to be implemented to reforestation plots infested with pocket gopher in the Pacific Northwest. This 1-year investigation assessed the efficacy of 0.15% cholecalciferol (vitamin D3) bait application to reduce pocket gophers and the long-term effects on non-target small rodent populations within treated plots. The study site was a reforested clear cut containing pocket gopher populations of 10 to 14 animals per ha. Six plots (2.8 ha each) were randomly selected at the study site, 3 plots of untreated controls and 3 plots baited with cholecalciferol. A trap-and-release program was used to assess non-target populations. Radio telemetry and the open hole method were used to monitor pocket gopher activity before and after the fall application of cholecalciferol bait. A 70-80% reduction of pocket gopher activity from telemetered animals occurred in the treated plots, whereas only 10-20% mortality occurred on the control plots. Pocket gopher activity in most of the plots increased by June, and by September of the following year, activity was back to original levels. Time, not treatment, had a significant effect on yellow pine chipmunk, Townsend chipmunk, and golden-mantled ground squirrel populations. We conclude that 0.15% cholecalciferol bait appears to have application for pocket gopher control. Risks to non-target species may exist.

CRYPTIC SPECIES IN THE MEXICAN POCKET GOPHER CRATOGEOMYS MERRIAMI

A study of chromosomal variation in the Mexican pocket gopher Cratogeomys merriami revealed differences in diploid number that correspond to 3 major genetic and morphological clades within the species. Each of these 3 clades is diagnosable based on multiple characters, including chromosomal diploid number, quantitative and qualitative morphological characters, and mitochondrial DNA. Accordingly, we restrict the name C. merriami (Thomas) to include only pocket gophers of this genus from the states of Mexico, Mexico D.F., northern Morelos, and west-central Puebla. We resurrect the species name C. fulvescens Merriam to represent members of this genus from southern Tlaxcala, east-central Puebla, and parts of west-central Veracruz. Finally, we resurrect the species name C. perotensis Merriam to represent members of this genus from southern Hidalgo, northern Tlaxcala, north-central Puebla, and parts of west-central Veracruz. Based on the observation that differences in diploid number usually signal reproductive isolation between populations of pocket gophers, we hypothesize that C. merriami, C. fulvescens, and C. perotensis are reproductively incompatible. We provide synonymies and descriptions for these 3 species, along with a key to the C. castanops species group to which these species belong.

Potential non-target risks from strychnine-containing rodent carcasses

Underground strychnine baiting is a common technique used to suppress pocket gopher ( Thomomys sp.) populations until seedlings are established. Non-target risks from underground baiting can still occur if strychnine-baited animals die aboveground. Accordingly, the fate of strychnine-baited carcasses of four small mammal species, Thomomys, Mus, Microtus, and Peromyscus, were documented during four trials on the Rogue River National Forest. We found no difference among species and type of damage, either insect or predator, during the four trials. However, survival differed between species in two trials where fewer Thomomys carcasses survived until completion of the study. We also examined the risk to tertiary non-targets from insects collected at the sites. Strychnine concentration among insect groups from treated carcasses differed with Diptera larvae and ants consistently containing higher concentrations. Even with high strychnine concentrations (0.2756 μg/g), risk assessments showed negligible tertiary risks from consuming strychnine-laced insects.

Process-based model linking pocket gopher (Thomomys bottae) activity to sediment transport and soil thickness

Burrowing organisms assist in shaping earth surfaces and are simultaneously affected by the environment they inhabit; however, a conceptual framework is not yet available to describe this feedback. We introduce a model that connects the population density of soil-burrowing animals to sediment transport via energy. The model, combined with avail- able data from California hillslopes where soil erosion is driven by pocket gophers ( Thom- omys bottae), suggests that a gopher annually expends ;9 kJ of energy, or ;1% of re- ported burrowing energy expenditure, in generating sediment transport. The model is used to evaluate the case that gophers prefer to populate thicker soils. The results suggest that this behavior may drastically dampen the spatial and temporal variations of soil thickness and gopher populations, implying that burrowing organisms may create landscapes dis- tinct from those affected by abiotic processes.

Effectiveness of trapping to control northern pocket gophers in agricultural lands in Canada

The northern pocket gopher (Thomomys talpoides) is considered a major pest in haylands, particularly alfalfa, and surrounding crops and shelterbelts of western Canada. Although poison baits are often used with the objective to quickly reduce pocket gopher populations over large areas, recent investigations in western Canada have demonstrated that they were ineffective in reducing and controlling pocket gopher populations in haylands. This paper identifies the elements of an effective pocket gopher control program and demonstrates that, with a proper strategy to lay out killing traps in spring to remove breeders-of-the-year, and to intercept invading pocket gophers, trapping is the most effective method to control northern pocket gophers. This paper also describes an effective trapping program and identifies research needs to increase capture efficiency.

Reinvasion dynamics of northern pocket gopher ( Thomomys talpoides) populations in removal areas

This study was designed to test the hypothesis that continuous removal of northern pocket gophers ( Thomomys talpoides) from natural habitats and tree fruit orchards would result in successful population reduction. A secondary objective was a detailed analysis of demographic responses (reinvasion dynamics) of gopher populations in control and removal sites. Pocket gopher populations were intensively live-trapped in replicate control and removal sites in natural and orchard habitats at Summerland and Vernon, British Columbia, Canada. New pocket gophers readily colonized removal sites in the natural habitats, particularly during spring, summer, and fall months. Fewer gophers colonized vacant sites during winter months (⩽1 per ha at Summerland and ⩽9 per ha at Vernon). Mean abundance of gophers ranged from 15 to 31 per ha on control sites. Population increases due to recruitment on control sites were reflected in periods of high reinvasion of removal sites. Spring reproduction and subsequent dispersal of juvenile gophers resulted in high colonization of vacant habitat. The recovery ratio (colonization rate) of gophers in natural habitats averaged 26.9% in summer and 0.9% in winter at Summerland, and averaged 44.2% in summer and 40.4% in winter at Vernon. Recovery ratios to previous densities on removal sites averaged >100% in summer at Summerland and in both seasons at Vernon. A relative recruitment index also followed this pattern at both study areas. New adult gophers that reinvaded removal sites produced young there despite continuous removal of animals. Mean body mass of gophers was significantly higher in control than removal populations at Summerland, but not Vernon. This study is the first intensive live-trapping evaluation of reinvasion dynamics of northern pocket gophers in removal sites. It seems likely that colonization of sites treated with toxicants or kill-trapping will be at least as high as the reinvasion rates recorded in our study. The timing of removals is crucial to achieving an overwinter reduction in gopher abundance.

A NEW SUBSPECIES OF POCKET GOPHER (GENUSGEOMYS) FROM THE OZARK MOUNTAINS OF ARKANSAS WITH COMMENTS ON ITS HISTORICAL BIOGEOGRAPHY

Nucleotide sequence analysis of the cytochrome-b gene of mtDNA and univariate and multivariate statistical analyses of cranial morphology were used to determine the evolutionary status of relictual, isolated populations of pocket gophers (genus Geomys) from the Ozark Mountains of Arkansas. Results of the mtDNA sequence analysis indicated that populations from the Ozark Mountains are most similar to G. bursarius missouriensis in Missouri and not to geographically proximate populations of G. breviceps. Morphological analyses were concordant with those results. Our findings confirm earlier work comparing similarities in allozymes and species-specific ectoparasites. Nucleotide sequence and morphological divergence between the Ozark populations and G. bursarius missouriensisare typical of differentiation between other subspecies of G. bursarius. We conclude that populations of pocket gophers isolated in the Ozark Mountains represent a discrete genetic entity and should be recognized as a new subspecies.

Fumigant dispersal in pocket gopher burrows and benefits of a blower system

Author(s): Nolte, Dale L.; Wagner, Kimberly K.; Trent, Andrew; Bulkin, Stephen | Abstract: Efforts to establish tree seedlings on sites infested with high populations of pocket gophers (Thomomys spp.) can be futile unless population control measures are implemented. Fumigants are a possible means to reduce pocket gopher populations although the efficacy of fumigants on reforestation sites has been minimal. We conducted a series of experiments to monitor the movement of carbon monoxide through burrow systems and to assess the potential benefits of a blower system. In the first experiment, carbon monoxide was introduced to an artificial burrow system by burning either one or two gas cartridges concurrently or consecutively. The blower was tried at different speeds for varied durations. Carbon monoxide concentration was monitored with sensors that had a detection range from 0 to 5,000 parts per million. Burning the cartridges without the blower was not effective in distributing carbon monoxide. The most effective fumigant dispersal occurred when the blower was used at a low speed for only the period while a cartridge was burning. Burning two cartridges simultaneously was the most effective burn configuration. Results from a second experiment, using vacated pocket gopher burrows instead of an artificial system, were similar to those recorded for the first experiment. Subsequently, we conducted field trials using a blower to disperse carbon monoxide to reduce pocket gopher populations on reforestation sites. These trials did not demonstrate a reduction in pocket gopher activity. We speculate this was because existing burrow plugs prevented the gas from dispersing through the systems or because pocket gophers rapidly blocked burrows when they detected the gas, thus preventing exposure to lethal gas concentrations.

Integrated management tactics for predicting and alleviating pocket gopher (Thomomys spp.) damage to conifer reforestation plantings

Pocket gophers cause extensive damage to reforestation plantings in the western United States, and pose acute and chronic problems for forest managers. We examine the components of an integrated pest management strategy for reducing pocket gopher damage to conifers: the predictive factors for assessing the risk for damage, techniques for monitoring gopher populations and assessing efficacy of control methods, and damage control strategies and methods. The information in each component is reviewed and presented so that an optimal damage reduction plan can be developed in a logical, cost-effective, environmentally responsible fashion.