EFFICACY OF 3 JN-BURROW TREATMENTS TO CONTROL BLACK-TAJLED PRAIRIE DOGS

CHARLES D. LEE, Department of Animal Science, Kansas State University Research and Extension, Manhattan, KS, USA JEFF LEFLORE , East Cheyenne County , Cheyenne Wells , CO, USA

Abstract: Management of prairie dog ( Cynomys ludovicianus) movement by colony expansion or dispersal may involve the use of toxicants to reduce local populations. Hazards associated with the use of toxicants cause concern for non-target species. Applying the bait in-burrow should reduce the primary exposure of the toxicants to non-target wildlife. Some literature suggests prairie dogs will not consume bait when applied in the burrow. In this trial we compared efficacy of Rozol ® (), Kaput-D Prairie Dog Bait ® (diphacinone), 2% oats applied in-burrow and 2% zinc phosphide oats applied on the surface. Results are reported as change in prairie dog activity.

Key words: chlorophacinone , control, Cynomys ludovicianus, diphacinone, in-burrow, management , prairie dog, toxicant , zinc phosphide

Proceedings of the I 2'h Wildlife Damage Management Conference (D.L. Nolte , W.M. Arjo, D.H. Stalman, Eds). 2007

INTRODUCTION This type of controversy has lead to scrutiny Control of black-tailed prame dogs of all types of control , especially the use of (Cynomys ludovicianus) is controversial on toxicants . Although there are numerous the Great Plains. Prairie dogs have been control techniques for prairie dogs, many controlled on rangeland for many years landowner s are dissatisfied with their largely with the use of toxicants applied consistency of efficacy and ease of use . above ground (Witmer and Fagerstone Most of the literature on black-tailed 2003). Most control efforts occurred prairie dog control using toxicants , report on because of perceived competition between efficacy when the product has been applied domestic livestock and prairie dogs for on the soil surface. Tietjen (1976) reported range forage (Forrest and Luchsinger 2006). prame dog act1v1ty was reduced Prairie dog s feed on many of the same significantly more when bait was applied on grasses and forbs that livestock do (Hansen the surface compared to when bait was and Gold 1977, Van Dyne et al. 1983). applied in the burrows. That report may Regardless of the debate surrounding the have caused future researchers to discount consideration of prairie dogs as a keystone in-burrow treatments. When toxicants are species, many species are associated with on the surface the product is more accessible the habitat they create (Kotliar 2000). Some to non-target species especially birds. Lee groups are concerned about the long-tem1 et al. (2005) reported success with an in­ viability of prairie dog populations. Some burrow toxicant to reduce burrow reopening counties or townships require eradication of by prairie dogs. This paper reports on the any prairie dogs (Lee and Henderson 1988). change in activity level of prairie dogs as

201 measured by three different techniques using differ significantly from the areas not three different toxicants , two of which are colonized by prairie dogs . Archer et al. applied in-burrow. (1987) reported vegetation change occurs as In the absence of management time of occupation increases . programs , the area occupied by prairie dogs Annual precipitation in the region can increase dramatically. Dogs on one averages 39 cm with about 57 cm of snow. ranch in Kansas increased the area occupied However this year an unusual weather event by prairie from I 05 ha in 2000 to 970 ha in blanketed the area with more than 100 cm of 2006 (Lee unpublished). That type of snow for more than 90 days while the study mcrease causes concern from those was underway . landowners who do not appreciate prairie No cattle were present on the areas dogs and whom may be neighbors to those while the study was in progress but the areas that do. Zinc phosphide (ZP) is the most had been grazed during the summer of 2006 . commonly used toxicant for prairie dogs that Colorado Department of Agriculture is applied on the surface (Witmer and reported no black-footed ferrets were Fagerstone 2003). Concerns about efficacy, present in the area so it was not surveyed for bait avoidance, extra labor involved with ferrets. Some avian species observed on the pre-baiting and the potential exposure to area during the study included homed lark birds and other non-target wildlife to toxic (Eremophifa alpestris), western meadowlark bait cause managers to seek alternatives to (Sturnella neglecta), mournmg dove zinc phosphide applied on the surface. (Zenaida macroura), northern harrier (Circus cyaneus), and burrowing owl STUDY AREA (Athene cunicularia). The only mammal We conducted the study on 4 black­ observed on the site other than prairie dog s tailed prairie dog colonies in eastern was a jackrabbit (Lepus californi cus). Colorado during December 2006 to March 2007. The colonies varied in size from 4.8 MATERIALS to 12.6 ha. The colonies have been The grain baits tested were: Kaput-D established for severa l years, but their exact Prairie Dog Bait (0.0025% diphacinone), 54 age is unknown . Colonies were not g, Scimetrics, LTD Corp., Wellington, CO.; randomly selected but picked due to size and Rozo ! (0.05% chlorophacinone), 53 g, proximity to each other but still isolated Liphatech , Inc., Milwaukee, WI. ; ZP Rodent from other colonies. Each complete colony Bait AG (2% zinc phosphide) , 4 g, Bell was treated to reduce problems with Laboratories, Madison, WI. Reference to emigration or immigration by prairie dogs products does not imply endorsement. from other colonies. This study site had no Kaput-D and Rozol have the active other untreated prairie dog colonies within ingredient applied on dyed wheat, however , 6.4 km. All four treated sites were within a Tietjen (l 976) reported that prairie dogs did 1.8 km radius of each other and the closest not consume wheat as well as other grains any colony was to another was 0.8 km. We such as oats , barley or milo. suspect no inter-colony movement occurred The baits (Kaput-D at this time of year. and Rozol) are vitamin-K antagonists that The dominant vegetation was disrupt blood clotting mechanisms and buffalograss (Buchfoe dactyo ides) and blue induce capillary damage (Pelfrene 1991). grama (Bouteloua gracilis) with few forbs Death results from hemorrhage and exposed present. The vegetation did not appear to animals may exhibit increasing weakness

202 prior to death. Zinc phosphide is a non­ The test baits were applied by a anticoagulant and occurs as an qualified applicator licensed by the State of inorganic compound whose toxicity results Colorado. Baits were applied the day from liberation of gas from following the pre-treatment census. Bait reaction of the active ingredient with water application was made to all active prairie and acid in the stomach (Hygnstrom et al. dog burrows, which were identified by 1994) . Death can occur within a few hours visual observation of bu1Tow openings that of ingestion . were generally free of leaves , other debris or spider webs, and/or showed freshly turned METHODS earth, and/or had prairie dog feces nearby. All colonies were measured with a One-quarter cup of bait was placed into each global positioning system (HP-L4 GPS unit, active burrow for the anticoagulant baits. Corvallis Microtechnology, Corvallis, OR) Sites that were to be treated with 2% zinc to determine area of coverage, location and phosphide were prebaited with one teaspoon orientation . Three different census methods of clean oats applied either in-burrow or on were utilized. A visual count with two scans the surface near the burrow entrance using 7 x 35 power binoculars after a 15 corresponding with the treatment protocol. minute acclimatization period was One day later, the zinc phosphide oats were conducted within 1 to 4 hours post sunrise applied either in-burrow or on the surface. and a visual count index conducted within l Bait application was made by hand from an to 4 hours prior to sunset were the direct A TV . A flexible hose and funnel was used census methods used to estimate prairie dog for in-burrow treatments . All bait populations. A plugged burrow index with treatments were applied only one time . 50 burrows plugged per site and the A methodical carcass search of the reopened burrows counted 24 hours post complete treated plots was conducted twice plugging was used as an indirect census each day until day 19 when snow covered method (Tietjen and Matschke 1982) . Both the sites and we were no longer able to census methods were used before and after travel to the sites. Search grids were the baitin g application period , with the established about 40 m apart and driven visual count index taken before the plugged each day with the searcher looking out the burrow index , on all treated plots. The pre­ driver ' s side window. Prairie dogs treatment census was taken l day prior to discovered on the surface were collected and application of the bait. The post-treatment removed to limit their availability to census was to be taken 21 days after predators and scavengers . Carcass searches application of the bait, but deep snow were conducted both in the morning (to delayed the post-treatment census for 105 reduce likelihood of scavenging by raptors) days. The weather conditions were and in the afternoon (to reduce scavenging described as normal for the first two weeks by nocturnal predators). of the trial followed by an extended period The census methods were intended of ice and snow that covered the colony to a to "index" the population, and allow for a depth of more than 91 cm for more than 90 comparison of the index measurements days. This depth of snow kept the prairie taken pre-treatment and post treatment. The dogs below ground for an extended period change in these population indices on treated of time. plots was calculated using the formula modified after Tietjen (1976):

203 % change Pre-treatment Cens us - Post-treatment Census X I 00 Pre-treatment Census

RESULTS AND DISCUSSION potential primary and secondary risks to The US Environmental Protection bird s and mammals (USEPA 2004) (Table Agency (EPA) has established a 70% 2). Use of that model indicates a wide minimum standard for efficacy (USEPA variance of risk among toxicants . As 1982). Not all treatments in this trial were contentious wildlife managers we should effective at reducing prairie dog activity strive to use products that are efficacious but which could be considered as a measure of also reduce risk to other wildlife in the efficacy . The means of the percent environment. That model would suggest reduction in activity ranged from 14 to that either chlorophacinone or dipahacinone 100% (Table I) . would pose less risk than zinc phosphide . A comparative analysis model has been used by the EPA to rank and compare

Table 1: Percent reduction of black-tailed prairie dog activity by applications of toxicants applied in-burrow and on the surface on variable-sized plots in eastern Colorado in 2006-2007.

Toxicant Survey Technique

Visual observation (am) Visual observation (pm) Burrow plugging Diphacinone (in-bu1Tow) 100 100 93 Chlorop hacinon e (in-burrow ) 100 100 100 Zinc phosphide (in-burrow) 21 16 14 Zinc phosphide (on surface) 50 49 45

Table 2: Comparative analysis model results for overall risk to birds and mammals. Tabulated values are weighted measures of effect (Modified from USEPA 2004).

Rodenticide mg ai/kg Primary Primary Secondary Secondary risks Summary risk s risks risks Mammals Values Birds Mammals Birds

Brodifacoum 50 5.58 1.25 8.60 6.76 5.55 Bromoadiolone 50 0. 10 0.71 3.03 4.40 2.06 100 0.10 0. 10 2.20 0.44 0.7 l Chlorophacinone 50 0.07 0.08 0.03 7.62 1.99 750 0.12 0.18 2.00 2.00 1.07 50 0.01 0.22 3.18 8.42 3.01 Diphacinone 50 0.01 0.22 3. 18 8.42 2.96 250 0.04 0.83 1.72 1.32 0.98 Zinc phosphide 20,000 7.81 10.00 0.00 0.69 4.63

204 Zinc phosphide is the only product because it provides time to administer the with a federal registration for use on bait. antidote (vitamin Kl) to save pets, livestock , Such baits are classified as Restricted Use and people who may have accidentally Products and applicators must obtain ingested the bait. Chlorophacinone and certification from the EPA prior to using diphacinone are similar in potency. such baits. Zinc phosphide is often Chlorophacinone and diphacinone may kill recommended as the rodenticide of choice some rodents in a single feeding, but because it is fairly specific for rodents and multiple feedings are needed to give there is no true , except adequate control of an entire population possibly in dogs and cats. Most animals (Clark 1994, Hygnstrom et al. 1994). that feed on rodents are unaffected because The use of to manage the zinc phosphide does not accumulate in prairie dogs bas been investigated by other the rodent's muscles or other tissues researchers (Mach et al. 2002 , Sullins 1990). (Matschke et al. 1992). Johnson and Such efforts have failed to obtain a federal Fagerstone (1994) reviewed the hazards of registration for their use. Under authority of zinc phosphide to wildlife and concluded it Federal Insecticide , Fungicide and showed few risks to nontarget wildlife when Rodenticide Act, Section 24( c ), several properly applied. Nationwide, there have states have allowed use of anticoagulants as been poisonings of all species of domestic a Special Local Need registration. These livestock, dogs and cats but these are usually labels require the products to be placed into accidental exposures and are few in number. the prairie dog burrow where the product is Many species of animals are subject to zinc not accessible to other animals. With these phosphide poisoning , but avian species, compounds, feeding does not always have to specifically gallinaceous birds , are the most be on consecutive days. When seriously affected (USEPA 2004). anticoagulants are eaten daily , however, Prebaiting with untreated oats several days death may occur as early as the third or prior to application of zinc phosphide is fourth day . In-burrow baiting would seem required by the label and increases efficacy to reduce hazards to most species of birds . (Tietjen and Matscbke 1982). Availability of carcasses found on Anticoagulant were first the soil surface may increase the risk to non­ discovered in the 1940s and have since target predators or scavengers. In this trial, become the most widely used toxicants for we only found four prairie dogs that had commensal rodent control. Rodents died on top of the ground. All were found in poisoned with anticoagulants die from the 4.9 ha colony that had been treated with internal bleeding, the result of loss of the Kaput D prairie dog bait. A carcass was blood's clotting ability and damage to the found on day 8, two on day l O and one on capillaries. Prior to death, the animal day 12 of the trial. Some secondary hazards exhibits increasing weakness due to blood have been found on test animals that are fed loss, though appetite and body weight are carcasses of rodents killed with not specifically affected. Because chlorophacinone or diphacinone (USEPA anticoagulant baits are slow in action 2004). (several days following the ingestion of a This trial looked at different survey lethal dose), the target animal is unable to techniques to determine activity. Severson associate its illness with the bait eaten. and Plumb ( 1998) reported that burrow Therefore, bait shyness does not occur. This plugging is not an adequate measure of delayed action also has a safety advantage prairie dog population densities and suggest

205 visual observations are more accurate. The FORREST, S., AND J. LUCHSINGER. 2006. Past percent reduction in prairie dog activity and current chemical control of prairie during this trial was similar regardless of the dogs. Pages 115-128 in J. Hoogland , survey technique used (Table I). editor. Conservation and Management Most ranchers want I 00% mortality , of Prairie Dogs, Island Press , Washington University, St. Louis , MO. although it is difficult to obtain I 00% HANSON, R.M ., AND I.K. GOLD. 1977. Black­ mortality in a single treatment regardless of tailed prairie dogs , desert cottontails and the product used. Because colonies cattle trophic relations on shortgrass frequently recover almost completely within range. Journal of Range Management 3 years after a single poisoning, retreatment 30:210-214. until 100% mortality is achieved is often the HYGNSTROM, S.E., R.M. TIMM, AND G.E. goal (Collins et al. 1984, and Ada et al. LARSON. 1994. Prevention and Control 1990). Repeat treatments with zinc of Wildlife Damage . University of phosphide are not as successful as initial Nebraska Cooperative Extension, efforts (Andelt 2006). This trial showed USDA Animal Damage Control, and reduction in activity close to l 00% with a Great Plains Agriculture Council. JOHNSON,O.H ., AND K.A. FAGERSTONE.1994 . single application of either anticoagulant Primary and secondary hazards of zinc Rozol or Kaput-O Prairie Dog Bait applied phosphide to nontarget wildlife-a review in-burrow. of the literature. USDA, APHIS, Denver Wildlife Research Center Research LITERATURE CITED Report No. 11-55-005, Denver , CO. ANDELT, W.F. 2006. Methods and Economics of KOTLIAR, N.B. 2000. Application of the New managing prairie dogs . Pages 129-138 Keystone-Species Concept to Prairie in J.L. Hoogland , editor. Conservation Dogs: How well does it work? of the black-tailed prairie dog: saving Conservation Biology 14 6: 1715- 172 1. North America's western grasslands, LEE, C.D., AND F.R. HE DERSON.1989. Kansa s Island Press, Washington University, St. attitudes on prairie dog control. Louis, MO. Proceedin gs of the Great Plains Wildlife ARCHERS., M .G. GARRETT,AND J .K. DETLING. Dama ge Control Workshop 9: 162-165. 1987. Rates of vegetation change __ , P.S. GIPSON,A D J.J. WILSON.2005. In­ associated with prairie dog (Cynomys burrow application of Rozo] to manage ludovi cianus) grazing 111 North black-tailed prairie dogs . Proceedings of American mixed-grass praine. the Wildlife Damage Management Vegetation 72: 159-166. Conference 11:349-353. ADA, A.O., 0.W. URESK, /\ D R.L. LINDER. MACH, J.J., S.E. HYGNSTROM, AND R.M. 1990. Black-tailed prame dog POClfE. 2002. Laboratory etlicacy study populations one year after treatment of six concentrations of warfarin bait for with rodenticides. Great Basin Naturali st black-tailed prairie dogs. International 50:301-309. B iodeterioration and Biodegradation CLARK, J.P. 1994. Vertebrate Pest Control 49 : 157-162. Handbook. 4th Edition. Division of MATSCHKE, G. H., K.J. ANDREWS,AND R.M . Plant Industry , Integrated Pest Control ENGEMAN. 1992. Zinc phosphide : Branch. State of California Depaiiment Black-tailed prairie dog-domestic ferret of Food and Agriculture. secondary poisoning study. Proceedings COLLfNS, A.R. , J.P. WORKMAN, AND D.W . of the Vertebrate Pest Conference URESK. 1984. An economic analysis of 15:330-334. black-tailed prame dog (Cynomys PELFRENE, A.F. 1991. Synthetic orgamc ludovicianus) control. Journal of Range rodenticides. Pages 1271-1316 in J.J. Management 3 7:358-36 l. Hayes Jr., and E.R. Laws Jr., editors.

206 Handbook of Pesticide Toxic o logy, volume 3: C lasses of Pes ticide s, Academic Pre ss, Inc ., San Diego, CA. SEVERSON, K.E. AND G.E. PLUMB. 1998. Comparison of method s to estimate population densiti es of black-tailed prairie dogs . Wildlife Society Bulletin 26( 4 ):859-866. SULLfNS, M. 1990. Use of chlorophacinone treated bait for management of black- tail ed prame dogs 111 Montana. Unpublished Report. Montana Department of Agriculture, Helena , MT. TIETJEN, H.P. 1976 . Zinc pho sphide: Its development as a control agent for black-tailed prairi e dog s. United States Fish and Wildlife Service , Special Scientific Report No. 195. Wa shington D .C. TIETJEN, H.P., AND G.H. MATSCHKE. 1982. Aerial pre-baiting for manag ement of prairi e dogs with zinc pho sphide . Journal of Wildlife Management 46: l 108- I l l 2. UNITED STATES ENVIRONMENTAL PROTECTION AGENCY. 1982. Pesticid e assess ment guid elines, subdi vision G: product performance (96-13: Rodent Fumigants) . Pa ges 3 16-3 18 EPA-540 /9- 82-026. Office of Pesticide Pro gra ms, Washington , D .C . . 2004. Potential risks of nin e roden ticides to bird s and nont arge t mamm als: a co mpara tive approach. Office of Pesticide Program s, Wa shin gto n, D.C. VAN DYNE, G .M., J.D. HANSON, AND R.C. JUMP. 1983. Seaso nal changes in botanica l and chemical composition and di ges tibility of diets of large herbivor es on short grass prairie . Proc eedin gs of the Int ernational Grass land Co ngress, 14:684 -68 7. WITMER, G.W., AND K.A. fAGERSTONE 2003. Th e use of toxicant s in black-tailed prairie dog manag ement: An overview. Proc eedings of the Wildlife Dam age Mana gement Co nference 10:359-369.