Richard C. Rosatte

RACCOON AND SKUNK POPULATION MODELS FOR URBAN DISEASE CONTROL PLANNING IN ONTARIO, CANADA

Population data on raccoon (Procyon lotor) and striped skunk (Mephitis mephitis), collected between 1987 and 1996 in the city of Scarborough (Ontario, Canada), were used to develop spatially explicit population models for use in disease control planning. The objective of model development was to: (1) provide a standard analytical method to identify areas of high-density raccoon and skunk subpopulations within cities, and (2) to identify those subpopulations predicted to function as sites of high dispersal (either into or out of subpopulations). These areas could be targeted in disease control programs. The models combined landscape map data with a stochastic, age-structured population model, which incorporated habitat-specific demographic data and functions relating to animal dispersal. Using this approach, the assemblage of raccoons and skunks inhabiting Scarborough was modeled as occupying discrete subpopulations linked by dispersal (i.e., a metapopulation). The landscape data used in this study were de...

Contact rates of raccoons (Procyon lotor) at a communal feeding site in rural eastern Ontario.

Intra- and interspecific contact rates of 12 adult (five females, seven males) raccoons (Procyon lotor) were recorded while these animals fed at a rural garbage dump 40 km north of Kingston, Ontario, Canada from 15 June to 5 September 1995. While raccoons were being observed, they bit, and were bitten, by their conspecifics an average of 0.99 (±0.21) and 1.28 (±0.21) times per hour, respectively, while feeding. Based on mean nightly contact rates (which included time when raccoons were not observed), raccoons bit one of their conspecifics once every 3 nights while feeding. The mean rate of bites made and received per hour for males was not significantly different from lactating females. There was no detectable difference between the mean rate of bites made and received per hour for raccoons which regularly versus occasionally fed at the dump. No interspecific contacts were observed, though raccoons and striped skunks (Mephitis mephitis) often fed at the dump concurrently. The contact rates in this study are the first to be calculated for raccoons directly from field data and will be useful as a point of reference for modeling rabies spread in raccoons in areas with similar site characteristics.

Rabies Control in Wild Carnivores

The control of rabies in wild carnivores has evolved from culling operations targeting vector species, to parenteral and oral vaccination of free-ranging vector populations. In order for a rabies control program to be successful, many variables must be evaluated including the timing of control tactic implementation, the ecology of the rabies vector species, and the density of vaccine-baits required to immunize the target population at a level that will result in the control or eradication of rabies from the target zone. Key to the effective control of rabies in wildlife populations, and prevention of re-initiation of outbreaks following control, will be restrictions on the importation of wildlife species that are at risk of importing disease pathogens such as rabies. It has been proven, both in Europe and in North America, that large-scale oral rabies vaccination programs targeting wild carnivore populations can be cost-effective as well as effective at controlling and eliminating rabies. Key to continued success of wildlife rabies control operations will be the design of effective contingency plans to respond to re-emergence of the disease as well as rabies management plans formulated by multi-jurisdictional collaborations at the international level.

NUMERICAL RESPONSE OF FISHERS TO SYNCHRONOUS PREY DYNAMICS

Abstract Fisher (Martes pennanti) populations may respond numerically to fluctuating hare populations, although uncertainty remains about this contention. We analyzed livetrapping data from Ontario (448,654 trap nights) that contained trend information for fishers, lagomorphs (snowshoe hares [Lepus americanus] and eastern cottontails [Sylvilagus floridanus]), and North American porcupines (Erethizon dorsatum) for 1995–2004. The data encompassed a synchronous fluctuation of lagomorphs and porcupines. Fisher populations appeared to have a delayed, positive numerical response with a lag of 2 years to changing lagomorph abundance, but they also appeared to switch to an unmeasured, alternate prey during the lagomorph low. This finding suggests that fishers are generalist predators that should have a stabilizing effect on the predator–prey system.

Development of a Sightability Model for Low-Density Elk Populations in Ontario, Canada

Abstract The status of recolonizing elk (Cervus elaphus) populations in Ontario, Canada, is unclear and there is a need for effective population survey methods that can be applied locally. We sought to develop a sightability model that could account for both low densities of elk and dense forest cover in elk-release areas in Ontario. We corrected winter aerial survey counts for sightability based on radiocollared animals known to be within observable distance of the aircraft. The multivariate model with the highest Akaikes Information Criterion corrected for sample size weight (wi = 0.427) revealed that elk group size, elk activity, dominant tree type, percent canopy cover, and percent conifer cover were significant predictors of elk sightability. The group-size effect indicated that odds of sighting an elk increased by 1.353 (95% CI = 0.874–3.689) for every additional elk. Standing elk were 5.033 (95% CI = 0.936–15.541) times more likely to be observed than were resting elk, and those located in conifer cover were 0.013 (95% CI = 0.001–0.278) times less likely to be sighted than elk in deciduous cover. Furthermore, elk located in >50% canopy cover and >50% conifer cover were 0.041 (95% CI = 0.003–0.619) times and 0.484 (95% CI = 0.024–9.721) times less likely to be sighted than elk in more open habitat, respectively. During model validation, observers detected 79% (113/143) of known elk in any given area, and population and sightability model predictions (±90% CI) overlapped with the population estimate, implying that our predictive model was robust. Unsurprisingly, large groups of elk in open habitat increased model precision, which highlights difficulties of counting Ontario elk in their northern range. We conclude that our model provided increased reliability for estimating elk numbers in Ontario compared to existing methods, and that the estimator may be useful in other areas where elk density is low and sightability is poor due to dense forest cover.

Acceptance of baits for delivery of oral rabies vaccine to raccoons.

During 1993–96 the Ontario Ministry of Natural Resources (Canada) implemented a research project to evaluate the efficacy of three candidate baits to deliver oral rabies vaccine to wild raccoons (Procyon lotor). Extensive field testing revealed that raccoon acceptance of Sugar-Vanilla baits (SV) at densities of 200/km2 and 400/km2, hand-placed in urban habitats of Scarborough (Ontario) during 1993, was 74% and 82%, respectively. Raccoon density in those areas averaged 11/km2. Aerial placement of SV baits in rural habitats in Barrie (Ontario) during 1993 and 1994, yielded raccoon acceptance levels of 58% with a density of 100 baits/km2, 59% at 75 baits/km2, and 47% at 50 baits/km2. Raccoon acceptance of SV baits was significantly lower in areas baited at the density of 50/km2. Acceptance of Cheese baits (CH) at a density of 75 baits/km2 was 52%. During 1996 trials in Barrie, modified SV baits with blister packs protruding through the matrix yielded raccoon acceptance values of 51% at a bait density of 54/km2, whereas acceptance of regular SV baits was 39% at a density of 51 baits/km2. Pooling of bait acceptance data for all years revealed that bait acceptance was highest for adult male raccoons. Raccoon density in rural habitats (Barrie, Ontario) where the studies took place, averaged 11–13/km2. Puncture and impact testing of blister packs in baits suggested that they would adequately serve as a vehicle to contain oral rabies vaccine for delivery to raccoons via baits.

Effect of canine distemper on an urban raccoon population: an experiment

Large-scale experiments about the effect of disease on wildlife populations are rare. We examined (1) whether the prevalence of canine distemper (CD) could be reduced in urban raccoons (Procyon lotor) using field vaccination and (2) the extent to which CD might limit raccoon populations. From May 1991 to November 1993, raccoons in a treatment area were trapped, vaccinated, and released at the site of capture. Population responses were monitored in treatment and control areas using information from a municipal animal control agency. During a CD epizootic, the prevalence of infected animals detected at necropsy from a sample of the population was significantly lower in the treated area (1.4%) than in the control area (8.3%). Patterns of population change did not differ between the treatment and control areas before, during, or after the epizootic, indicating that CD did not limit the raccoon population. Thus, field vaccination can result in reduced disease prevalence, but will not necessarily result in increased raccoon abundance.

Development of baits to deliver oral rabies vaccine to raccoons in Ontario.

During 1993, the Ontario Ministry of Natural Resources, Rabies Research Unit, conducted experiments to develop a bait that would be attractive to raccoons (Procyon lotor) and serve as a vehicle to deliver oral rabies vaccine to that species. Testing of six candidate baits on captive and wild raccoons revealed that the best baits in terms of attractiveness to raccoons were a sugar-vanilla bait and a cheese powder bait. Further testing of those two baits containing miniature radio-transmitters indicated there was no preference between the baits, with respect to acceptance by raccoons; however, as there were fewer problems in mass producing the sugar-vanilla bait, it was selected for larger scale experiments.

Genetic Tracking of the Raccoon Variant of Rabies Virus in Eastern North America

To gain insight into the incursion of the raccoon variant of rabies into the raccoon population in three Canadian provinces, a collection of 192 isolates of the raccoon rabies virus (RRV) strain was acquired from across its North American range and was genetically characterized. A 516-nucleotide segment of the non-coding region between the G and L protein open reading frames, corresponding to the most variable region of the rabies virus genome, was sequenced. This analysis identified 119 different sequences, and phylogenetic analysis of the dataset supports the documented history of RRV spread. Three distinct geographically restricted RRV lineages were identified. Lineage 1 was found in Florida, Alabama and Georgia and appears to form the ancestral lineage of the raccoon variant of rabies. Lineage 2, represented by just two isolates, was found only in Florida, while the third lineage appears broadly distributed throughout the rest of the eastern United States and eastern Canada. In New York State, two distinct spatially segregated variants were identified; the one occupying the western and northern portions of the state was responsible for an incursion of raccoon rabies into the Canadian province of Ontario. Isolates from New Brunswick and Quebec form distinct, separate clusters, consistent with their independent origins from neighboring areas of the United States. The data are consistent with localized northward incursion into these three separate areas with no evidence of east-west viral movement between the three Canadian provinces.

Rabies Control: An Adaptive Management Approach

Theoretically, disease can regulate populations, but experimental evidence to support or refute the theory is lacking. We used an ongoing disease management program to design a controlled field experiment to test whether rabies limits urban populations of striped skunks (Mephitis mephitis) to the extent that rabies eradication or reduction leads to increased skunk abundance. From 1987 to 1994, field vaccination of skunks occurred in a 60-km 2 area of Scarborough, Ontario, Canada. We used data on nuisance animal removal from 1985 to 1993 to estimate skunk abundance in the treated area and the rest of Scarborough, and we used the number of rabies-positive skunks submitted for testing as an index of rabies prevalence throughout the city. There was no difference (P < 0.05) in abundance patterns of skunks between the treated and untreated areas. Therefore, either rabies did not affect skunk abundance, or field vaccination did not reduce rabies. Only 4 rabid skunks were submitted for testing in 7 years after vaccination versus 28 in 3 years prior to vaccination. Hence, there has not been an epizootic of rabies in the city since vaccination began. Therefore, we are currently unable to determine whether field vaccination reduces rabies prevalence, and thus whether rabies reduction results in larger host populations. Decreased rabies and increased skunk abundance in the treated area may lead prematurely to the conclusion that field vaccination reduced rabies prevalence and resulted in increased host abundance. Similar results in the reference area, however, indicated that the observed effects were more likely an artifact of the timing of the vaccination program with respect to the rabies cycle versus a result of the treatment. Therefore, our study illustrates the importance of controlled field experiments in gaining reliable knowledge. We recommend that the experiment be continued until a rabies epizootic occurs.