Research Article Raccoon Density and Movements After Population Reduction to Control Rabies RICK ROSATTE, 1 Ontario Ministry of Natural Resources, Trent University, DNA Building, 2140 East Bank Drive, Peterborough, ON K9J 7B8, Canada KIRK SOBEY, Ontario Ministry of Natural Resources, Trent University, DNA Building, 2140 East Bank Drive, Peterborough, ON K9J 7B8, Canada DENNIS DONOVAN, Ontario Ministry of Natural Resources, Trent University, DNA Building, 2140 East Bank Drive, Peterborough, ON K9J 7B8, Canada MIKE ALLAN, Ontario Ministry of Natural Resources, Trent University, DNA Building, 2140 East Bank Drive, Peterborough, ON K9J 7B8, Canada LAURA BRUCE, Ontario Ministry of Natural Resources, Trent University, DNA Building, 2140 East Bank Drive, Peterborough, ON K9J 7B8, Canada TORE BUCHANAN, Ontario Ministry of Natural Resources, Trent University, DNA Building, 2140 East Bank Drive, Peterborough, ON K9J 7B8, Canada CHRIS DAVIES, Ontario Ministry of Natural Resources, Trent University, DNA Building, 2140 East Bank Drive, Peterborough, ON K9J 7B8, Canada ABSTRACT Population reduction (PR) and trap–vaccinate–release (TVR) were used to control an outbreak of the raccoon ( Procyon lotor ) variant of rabies in Ontario, Canada, during 1999. Raccoon density declined significantly following PR; however, density increased significantly 9–10 months post–PR. Recolonization of PR areas with raccoons marked in TVR areas was very low with only 1.8 % (32/1,759) of those raccoons dispersing into PR areas during 1999–2000. In addition, the number of raccoons dispersing from TVR areas into PR areas was not significantly greater than the number of raccoons dispersing into treatment areas where population reduction had not been implemented during 1999–2000. Raccoon movements in this study, determined by mark–recapture, averaged , 4.0 km during 1999–2000 and did not differ among treatments (with or without PR). In summary, there was not a mass exodus of raccoons from TVR areas to PR areas during 1999–2000, suggesting there was not an immediate, dramatic, vacuum effect drawing raccoons into areas devoid of raccoons due to PR. However, one year post–PR, raccoon populations were near or above pre–PR densities (due to a high reproductive rate of resident raccoons), suggesting that PR would have to be an annual event if rabies is not eliminated from an area. (JOURNAL OF WILDLIFE MANAGEMENT 71(7):2373–2378; 2007) DOI: 10.2193/2006-549 KEY WORDS density, movements, Ontario, population reduction, Procyon lotor , rabies control, raccoons, vacuum. Reducing the density of wildlife rabies vector populations to control diseases has been used in many areas of North America and Europe with varying degrees of success and failure (Rosatte et al. 1986, 2001; MacInnes 1987, 1988; Debbie 1991). One theory (which we will refer to as the Nature Abhors a Vacuum Theory; NAAV) to explain why wildlife depopulation programs generally are not effective for disease control in the long term is that depopulated areas are quickly recolonized by immigrating animals (Rosatte et al. 1986). The NAAV theory assumes density dependence and resource limitation as the keys to animal immigration into areas that have been depopulated. Understanding these processes is important because they may dictate the most feasible rabies control tactic to implement. As far as we know, the NAAV theory has never been tested for raccoon ( Procyon lotor ) populations. In Ontario, Canada, population reduction of wild raccoon populations was one of several tactics that was used to control raccoon rabies when the disease was first reported in that Province during July 1999 (Wandeler and Salsberg 1999, Rosatte et al. 2001). The objectives of this study were 1) to determine the extent of immigration, movement, and density of raccoons in areas where population reduction programs had been implemented to control rabies during 1999 and 2) to determine the density and movement of raccoons in areas where population reduction had not been initiated. If recolonization of depopulated areas by immi- grating raccoons occurs as a rapid event, then population reduction probably would not be the most feasible tactic to implement to control rabies in raccoons. STUDY AREA The study area, located in eastern Ontario, Canada, is dispersed with glacial moraines and plains with sandy deposits and some marshy areas. The dominant vegetation types included sugar maple ( Acer saccharum ), beech ( Fagus grandifolia ), yellow birch ( Betula alleghaniensis ) and red maple ( A. rubrum ). Crops in agricultural areas were primarily corn and alfalfa. The primary mammalian species in the study area included raccoon, striped skunk ( Mephitis mephitis ), fox ( Vulpes vulpes ), cat ( Felis catus ), cottontail ( Sylvilagus floridanus ), fisher ( Martes pennanti ), porcupine ( Erethizon dorsatum ), squirrel ( Sciurus carolinensis ), and mice and moles (various cricetidae). The area also supported a high density of white-tailed deer ( Odocoileus virginianus ). METHODS Commencing July 1999, 3 point infection control programs (PIC) were implemented to control the raccoon variant of rabies in eastern Ontario (Wandeler and Salsberg 1999, Rosatte et al. 2001; Fig. 1). Retrapping of those areas during the spring of 2000, where population reduction had been 1 E-mail: rick.rosatte@ontario.ca Rosatte et al. Racoon Density and Movements 2373 implemented during 1999 (which we will call treatments 1, 2, 3), provided data that would assist in supporting or refuting the NAAV theory of raccoon immigration. We compared those data to 3 experimental control areas (treatments 4, 5, 6) where population reduction had not been previously implemented. Point infection control included live-trapping (Tomahawk live-trap, Tomahawk, WI) and humanely euthanizing raccoons and skunks (via an injection of a euthanasia agent) within a 5-km radial area (population reduction zone [PR]) around the location of a case of raccoon rabies (Rosatte et al. 2001). In addition, raccoons and skunks were live-trapped, ear-tagged (numbered size 3 for raccoons and 1 for skunks; National Band and Tag Company, Newport, KY), and vaccinated (Imrab t 3; Merial Inc., Athens, GA) against rabies by injection (trap–vaccinate–release [TVR]) in a radial zone 5–10 km outside of the PR (Rosatte et al. 2001). The third component of point infection control was the aerial distribution of rabies vaccine baits (Vaccinia-Rabies Glycoprotein [V-RG]) outside of the PR and TVR areas (see fig. 1 in Rosatte et al. 2001). The size of each of the treatment areas was determined by the movement potential of rabid and nonrabid raccoons as documented in Rosatte et al. (2001, 2006, 2007 a ). Following the 3 point infection control programs, which were implemented during July–September 1999, we selected 6 areas for treatment during 2000. They included the following: Treatment 1 During 3 April–26 May 2000, we live-trapped raccoons and skunks and euthanized as above (untagged raccoons and skunks only—ear-tagged raccoons and skunks from the 1999 program were revaccinated and released) in the PR portion (cells 1–8; 75-km 2 area; Fig. 2) of the PIC program implemented to contain the first case of raccoon rabies that occurred in July 1999. We trapped each cell for 8 nights during a 2-week period. During the first 4 nights of trapping, we used 75 traps per cell and during the second 4- night period, we used 25 traps per cell. Treatment 2 During 3 April–9 June 2000, we placed 100 live-traps (for 8 nights over a 2-week period) in each of 7 cells (cells 31–37; 75-km 2 area) in the PR portion of the PIC program implemented to control the second case of raccoon rabies in July 1999 (Fig. 2). We processed all tagged and untagged raccoons as above. Treatment 3 During 3 April–26 May 2000, we processed raccoons and skunks as above in the PR portion (cells 53–59; 75-km 2 area; Fig. 2) of the PIC program to contain the third case of raccoon rabies that occurred in September 1999. Trapping effort was the same as for treatment 1. Treatment 4, 5 We also collected raccoon density and movement data during 1999 and 2000 from 2 experimental control areas (34 trapping cells—410-km 2 area in total) that had not been previously depopulated during 1999 but where TVR programs were implemented along the St. Lawrence River Figure 1. Map showing the location of treatments 1–6 in eastern Ontario, Canada, where we studied raccoon density, 1999–2000. Figure 2. Raccoon movements in eastern Ontario, Canada, between July 1999 and August 2000, from trapping cells that were trapped–vaccinated– released to cells that were depopulated during July–September 1999 (treatments 1–3) and July–August 2000 (treatment 6). Numbers in figure within concentric rings represent the location of trapping cells in areas that were depopulated (cells 1–8; 31–37; 53–59) and where trap–vaccinate– release was implemented (cells 9–30; 38–52; 60–64) in response to the first 3 cases of raccoon rabies in Ontario, Canada, during 1999. Rings represent the boundary between areas that received population reduction versus areas that received trap–vaccinate–release. Numbers outside of the outer rings that are designated with a ‘‘ V-RG ’’ indicates areas that were live-trapped to assess the effectiveness of vaccinia-rabies-glycoprotein baits (V-RG) during September 1999 as opposed to trap–vaccinate–release treatment. Other numbers outside of the outer rings (cells 96–128) represent cells that were depopulated during June–August 2000. Arrows represent the direction and extent of movements by raccoons during July 1999 and August 2000 (treatments 1, 2, 3, 6). T 1–T3 represents treatments 1–3 as well as the location of the first 3 cases of raccoon rabies in Ontario. 2374 The Journal of Wildlife Management 71(7) 19372817, 2007, 7, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.2193/2006-549 by University Of Florida, Wiley Online Library on [24/01/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License to proactively prevent the spread of raccoon rabies in Ontario (Fig. 1). Treatment 6 During September–October 1999, we live-trapped raccoons and collected blood samples to determine the percentage of the raccoon population that contacted rabies vaccine baits (V-RG) distributed outside (treatment 6) of 3 PR areas during September 1999 (Rosatte et al. 2001; Figs. 1, 2). We ear-tagged and released those raccoons as described above. During June–August 2000, 2 additional population reduc- tion programs were implemented to contain cases of raccoon rabies. We used ear-tagged raccoons collected during those operations to determine raccoon movements in treatment 6 which had not been previously depopulated. Statistical Analyses We determined raccoon density estimates in areas where population reduction occurred (treatments 1–3) using a catch-per-unit effort removal model (Leslie plot with linear regression; Krebs 1989). We used a Student’s t -test to determine whether there were any detectable differences in pre– and post–PR program raccoon density and a correlation coefficient to determine if there was any association between raccoon density per cell, movement distance, and proximity of trapping cells to one another (Zar 1974). We also used a Spearman Rank Order Correlation to test differences in raccoon density in PR cells during 1999 and 2000 and the proportion of available raccoons dispersing into those cells (Statsoft, Inc. 2004). We determined density using capture– recapture data in a modified Petersen model for treatments 4, 5, 6 (Krebs 1989). We evaluated differences in raccoon densities among treatment areas using one-way analysis of variance (ANOVA) and assessed movement distances among and within treatment areas using a factorial ANOVA. We used a chi-square to determine if there were differences in the number of raccoons dispersing from TVR areas into population reduction areas in the treatment areas (Zar 1974). We preformed all descriptive and inferential statistical analyses using Statistica 6.0 (StatSoft, Inc., Tulsa, OK). RESULTS Raccoon Density As reported in Rosatte et al. (2001) during the 1999 PIC programs, about 83–91 % ( n ¼ 1,202) of the raccoons were removed from the PR zones around raccoon rabies cases 1–3 (treatments 1–3). This resulted in a change in density of 5.1–7.1 raccoons per km 2 before the PR programs to 0.6–1.1 raccoons per km 2 after the PR programs were completed. We ear-tagged a total of 1,759 raccoons during 1999 TVR operations in PICs 1–3 (treatments 1–3), which potentially were available to immigrate into the PR zones (Rosatte et al. 2001). Pre–PR density in those TVR areas during 1999 averaged 4.5–7.2 per km 2 (Rosatte et al. 2001). Treatments 1–3 (with PR) Treatment 1. —Raccoon density following PR was significantly lower (0.5 raccoons/km 2 ) than pre–reduction density (7.2 raccoons/km 2 ; P , 0.001) during July 1999 (Table 1). Raccoon density 9–10 months post–PR (1.5 raccoons/km 2 ; Apr–May 2000) was 300 % higher than raccoon density immediately following the reduction pro- gram in July 1999 (0.5 raccoons/km 2 ; P ¼ 0.087; Table 1). Only 1.3 % (10/767) of the raccoons that were ear-tagged in the TVR area of treatment 1 during July 1999 had immigrated into the PR area by April–May 2000 (Fig. 2). Treatment 2. —Raccoon density following PR was significantly lower (1.4 raccoons/km 2 ) than pre–reduction density (6.3 raccoons/km 2 ; P , 0.001) during July 1999 (Table 1). Raccoon density 8–9 months post–PR (3.3 raccoons/km 2 ; Apr–May 2000) was significantly higher than raccoon density immediately following the PR program in July 1999 (1.4 raccoons/km 2 ; P , 0.03; Table 1). About 1.4 % (11/785) of the raccoons that we marked in the TVR area of treatment 2 immigrated into the PR area by April– May 2000. Three raccoons marked in treatments 1 and 3 dispersed to treatment 2 (Fig. 2). Treatment 3. —Raccoon density following the PR program was significantly lower (0.7 raccoons/km 2 ) than pre–reduction density (3.5 raccoons/km 2 ; P , 0.001) during September 1999 (Table 1). Raccoon density in treatment 3, Table 1. Raccoon density in treatments 1–3 prior to, immediately after, and 9–10 months following population reduction (PR) programs to control raccoon rabies during 1999–2000 near Brockville, Ontario, Canada. Treatment Raccoon sample size a Pre–PR raccoon density (no./km 2 ) b Post–PR raccoon density (no./km 2 ) b Reduction in raccoon population density ( % ) Raccoon density 9–10 months post–PR c (no./km 2 ) Increase or decrease in raccoon density 9–10 months post–PR (no./km 2 ) x ̄ 95 % CL x ̄ 95 % CL x ̄ 95 % CL x ̄ 95 % CL 1 b 554 7.2 d 5.6–8.6 0.5 0–1.9 90.5 85–100 1.5 0.1–5.8 þ 1.0 2 b 484 6.3 d 3.5–10.3 1.4 0–5.3 78.7 48.5–100 3.3 d 0.6–11.0 þ 1.9 3 e 425 3.5 d 1.9–5.9 0.7 e 0.1–3.1 80.0 f 46.9–100 2.7 d 0.5–9.1 þ 2.0 a Sample size ¼ no. raccoons trapped during both periods. b We trapped each cell during Jul 1999 as part of a PR program and then retrapped 9–10 months later (Apr–May 2000); the cell no. for treatment 1 were 1– 8, for treatment 2 were 31–37, and for treatment 3 were 53–59. c Preparturition density. d Raccoon density prior to the population reduction program was significantly higher than density immediately following the PR program. e We trapped each cell during Sep 1999 as part of a population reduction program and then retrapped 7–8 months later (Apr–May 2000). f We removed an additional 117 raccoons from the 75-km 2 (i.e., all cells) PR area immediately following the initial 7 nights of trapping so actual density following PR would be slightly lower and % reduction higher. Rosatte et al. Racoon Density and Movements 2375 19372817, 2007, 7, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.2193/2006-549 by University Of Florida, Wiley Online Library on [24/01/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 7–8 months post–PR (2.7 raccoons/km 2 ; Apr–May 2000), was significantly higher than raccoon density immediately following the reduction program in September 1999 (0.7 raccoons/km 2 ; P , 0.01; Table 1). Only 1.9 % (4/207) of the raccoons that we ear-tagged in the TVR area of treatment 3 dispersed into the PR area by April–May 2000; however, 7 raccoons marked in treatment 1 immigrated to treatment 3 (Fig. 2). Treatments 4–6 (without PR) Treatment 4. —In TVR areas (213-km 2 area) along the St. Lawrence River (Fig. 1), where population reduction did not occur during 1999 and 2000, we captured 3,303 raccoons (2,276 different raccoons) during 1999–2000 operations. Mean raccoon density in those cells was 7.0/ km 2 (95 % CI ¼ 6.3–8.1) and 6.2/km 2 (95 % CI ¼ 6.0–6.5), respectively, during 1999 and 2000 (Table 2). Treatment 5. —In TVR areas (198-km 2 area) along the St. Lawrence River (Fig. 1), where population reduction did not occur during 1999 and 2000, we captured 2,023 raccoons (1,543 different raccoons) during 2000 operations. Mean raccoon density in those cells was 5.3/km 2 (95 % CI ¼ 4.6–6.3) and 5.7 (95 % CI ¼ 5.3–6.2) during 1999 and 2000, respectively (Table 2). Treatment 6. —In areas that we trapped to assess the effectiveness of V-RG baiting, we caught 300 raccoons in an 81-km 2 area during the autumn of 1999. Average raccoon density in those cells during September–October 1999 was 5.6/km 2 (95 % CI ¼ 4.5–7.5; Table 2). During June 2000, we euthanized raccoons ( n ¼ 858) during operations to control cases of raccoon rabies. Raccoon density in that 162-km 2 area prior to PR averaged 7.6(3.9–14.3)/km 2 (Table 2). Among-treatment (1–6) statistical comparisons. —We observed no differences among 1999 pre–PR raccoon densities in treatments 1–3 and the core cells of treatments 4–6 ( F [5, 31] ¼ 1.79, P ¼ 0.14; Tables 1, 2). Similarly, we could detect no differences between 1999 pre–PR raccoon densities averaged across treatments 1–3 and 4–6 ( F [1, 35] ¼ 0.99, P ¼ 0.33). Correlation Between Raccoon Density and the Number of Raccoon Dispersers We could detect no significant correlation between raccoon density in trapping cells following PR in 1999 and the number of raccoons dispersing to PR cells during April– May 2000 (Spearman R ¼ 0.015; P ¼ 0.94; Table 1). However, we detected a significant correlation between raccoon density in PR cells during April–May 2000 and the number of raccoons dispersing into those cells (Spearman R ¼ 0.45; P ¼ 0.03; Table 1). We found a negative correlation between the number of raccoon dispersers and the distance between trapping cells to which they dispersed (Spearman R ¼ 0.52; P , 0.05). Raccoon Movements Raccoon movements in treatments 1–3 (areas with PR). — We ear-tagged and released 1,759 raccoons in the TVR portion of treatments 1–3 during 1999. Only 1.8 % (32) of those raccoons dispersed into the PR areas of treatments 1–3 during 2000. We found a significant interaction between the age of raccoons when first captured and sex with respect to distances moved during subsequent recaptures ( F [1,23] ¼ 12.33, P ¼ 0.001). Whereas average movement distances were comparable between adult male (2.2 km; SD ¼ 1.2, n ¼ 15) and adult female raccoons (2.7 km; SD ¼ 2.6, n ¼ 4), juvenile male raccoons moved greater distances (9.8 km; SD ¼ 6.6, n ¼ 7) and juvenile females moved shorter distances (1.1 km; SD ¼ 0.6, n ¼ 6) during July 1999–May 2000. Raccoon movements in treatments 4–6 (areas with no PR). —We ear-tagged and released 2,093 raccoons in the TVR portions of treatments 4–6 during 1999. Only 2.3 % (47) of those dispersed into the core areas of the treatments during 1999–2000. That was not different from the percentage (1.8) of marked raccoons that we recaptured in the population reduction areas of treatments 1–3 ( P ¼ 0.35; v 2 ¼ 0.86). Mean movement for all sex and age classes of raccoons for treatments 4 and 5 was 2.39 km (SD ¼ 2.79; n ¼ 20) and for treatment 6 was 3.9 km (SD ¼ 6.2; n ¼ 27). We found no significant interaction between the age of raccoons when first captured and sex with respect to distances moved during subsequent recaptures in treatment 4, treatment 5( F [1,23] ¼ 0.04, P ¼ 0.83), or treatment 6 ( F [1,23] ¼ 3.34, P ¼ 0.08). Raccoon movements in treatments 1–6. —There were no among-area (treatments 1–6) differences in raccoon move- ments ( n ¼ 79) when we pooled sex and age data ( F [2, 76] ¼ 0.62, P ¼ 0.54). Table 2. Raccoon density in treatments 4–6 during 1999–2000 where population reduction programs had not been previously implemented in eastern Ontario, Canada, during 1999. Treatment a Sample size 1999 raccoon density (no./km 2 ) 2000 raccoon density (no./km 2 ) Increase or decrease in raccoon density between 1999 and 2000 (no./km 2 ) x ̄ 95 % CL x ̄ 95 % CL 4 3,303 7.0 6.3–8.1 6.2 6.0–6.5 0.1 5 2,023 5.3 4.6–6.3 5.7 5.3–6.2 þ 0.4 6 b 1,158 5.6 4.5–7.5 7.6 3.9–14.3 þ 2.0 a The no. of trapping cells in treatments 4, 5, and 6 was 17, 15, and 12, respectively. The size of treatments 4, 5, and 6 was 213 km 2 , 198 km 2 , and 162 km 2 , respectively. b In treatment 6 we trapped a 81-km 2 area (9 cells) in 1999 and a 162-km 2 area (12 cells) in 2000. We calculated density estimates for treatment 6 using data collected during Jun 2000. 2376 The Journal of Wildlife Management 71(7) 19372817, 2007, 7, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.2193/2006-549 by University Of Florida, Wiley Online Library on [24/01/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License DISCUSSION Population reduction has been used globally to control wildlife diseases such as rabies in species such as red foxes, arctic foxes ( Alopex lagopus ), raccoons, striped skunks, and coyotes ( Canis latrans ; Rosatte et al. 1986, 2001, 2007 b ; Debbie 1991). Although often controversial, and expensive (about $500.00/km 2 Canadian; Rosatte et al. 2001), this tactic has proven to be effective, especially in areas where the disease has yet to become enzootic. The reason for success is rabies vectors that are incubating the disease or those that are clinical are removed from the population. When vaccination is used as a control tactic, these animals are not normally protected due to vaccination failure and they remain in the population to spread the disease (Rosatte et al. 2007 a ). Population reduction has also been used with varying results to control raccoon populations due to their predation on waterfowl and turtle nests (Greenwood et al. 1990, Ratnaswamy et al. 1997). Regardless of the reason for implementing population reduction, that tactic may fail if insufficient raccoons are removed from the population, if population turn-over is rapid due to high reproductive rates, or if raccoon immigration into the control area is extensive. In this study, recolonization of PR areas with raccoons marked in TVR areas was very low. In fact, only 1.8 % of the raccoons captured in the PR areas of treatments 1–3, 7–10 months post–PR, had emigrated from TVR areas outside of the PR zones as evidenced by ear-tags. Unmarked raccoons not captured during 1999 PR or TVR programs may have immigrated into the PR areas, because only 55–91 % of those populations were captured during 1999 (Rosatte et al. 2001). Alternately, raccoons may have immigrated from areas beyond treatments 1–3. However, substantial immi- gration is unlikely, because generally raccoons are fairly sedentary and have home ranges of about 4 km 2 and movements generally , 50 km (Rosatte 2000). In fact, raccoon movements in this study, determined by mark– recapture, only averaged , 4.0 km. In summary, there was not a mass exodus of marked raccoons from TVR areas into PR areas during 1999–2000. Thus, in this case, population reduction was a feasible tactic for the control of raccoon rabies. In this study, raccoon density 9–10 months post– population reduction was significantly greater than raccoon density immediately following reduction. This was not surprising because an estimated 83–91 % of the raccoons in treatments 1–3 were euthanized. However, if few raccoons emigrated from TVR areas, why was there a significant increase in density prior to the parturition period? That may have been due to the immigration of raccoons not captured during depopulation programs or animals dispersing from beyond the TVR areas. What this means is that although mass recolonization of PR areas with raccoons from TVR areas did not occur, the increase in density means that raccoon populations would be near pre–control levels very rapidly. Density estimates during April–May 2000 were minimum estimates as juveniles were not yet available for capture. If juveniles are factored into the population (Rosatte 2000), raccoon density in treatments 1–3 during the summer of 2000 would have been higher than pre–population reduction densities. This means that although PR was effective at significantly lowering raccoon density during 1999, by the summer of 2000, populations were rebuilt to the extent that they would be susceptible to another outbreak of rabies. This means that either population reduction should be repeated or one would have to take the chance that all incubating and clinical animals had been removed from the population. Raccoon movement in treatments 1–3 where population reduction was implemented during 1999 was not more extensive than in areas where population reduction programs had not been initiated (treatments 4–6). In addition, we detected no significant correlation between raccoon density in treatments with PR and the number of raccoons dispersing to those treatment areas the following spring. This was surprising because one would suspect that areas that were practically devoid of raccoons would attract dispersing raccoons. However, for that to occur, one has to assume dispersal is density-dependent and areas outside of the depopulated areas are resource-limited. If we refer to the data in Rosatte et al. (2001), there were about 2,700 raccoons living in the 485-km 2 TVR areas directly surrounding the 225-km 2 area that was depopulated during rabies control operations in eastern Ontario during 1999. Conservatively, the reduction programs would have created space (225 km 2 ) for approximately 800–1,600 raccoons, depending on the carrying capacity of the habitat (Broadfoot et al. [2001] estimated that the carrying capacity in urban habitats of southern ON was about 50–60 raccoons/km 2 ). One would think that this area is large enough to stimulate immigration if resources were limited. This study has shown that raccoon dispersal was not linked to density and in all likelihood, resources for raccoons are not limiting in southern Ontario due to the abundance of agricultural lands. Because raccoons in southern Ontario are probably well below the carrying capacity of the land, emigration to PR areas may not have been advantageous. That is, if resources are not limiting for raccoons, why would they move to a new area? This study leads to the conclusion that population reduction of raccoons does not immediately evoke a mass immigration of raccoons from the surrounding vicinity (5– 10 km); in other words, the vacuum theory is not as powerful as one would imagine, at least in this study. However, some immigration may have occurred by raccoons not euthanized during PR programs or animals immigrating from outside of the treatment areas. Regardless, due to the high reproductive rate of raccoons, population density is quickly reestablished following population reduction. MANAGEMENT IMPLICATIONS Population reduction of a rabies vector species such as the raccoon can be an effective disease control tactic (Rosatte et al. 2001). In this study, immigration of raccoons into the PR area Rosatte et al. Racoon Density and Movements 2377 19372817, 2007, 7, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.2193/2006-549 by University Of Florida, Wiley Online Library on [24/01/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License from the immediate (5–10 km) area did not occur as a rapid event. However, a high reproductive rate and large litter sizes for raccoons accounts for rapid population growth with popu- lations only requiring 1–2 years to rebuild to pre–population- reduction levels. In view of this, PR would have to be an annual event in order to eliminate rabies from an infected area. ACKNOWLEDGMENTS The Ontario Ministry of Natural Resources (OMNR) wildlife rabies control program is supported by the Ontario Rabies Advisory Committee and the OMNR Wildlife Research and Development Section, Peterborough, Ontario. 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