Raccoon Populations Research Articles

First North American field release of a vaccinia-rabies glycoprotein recombinant virus.

Following nearly 10 yr of extensive laboratory evaluation, a vaccinia-rabies glycoprotein (V-RG) vaccine was the first recombinant virus to undergo limited North American field release on 20 August 1990. The free-ranging raccoon population on Parramore Island (Virginia, USA) was exposed to a high density (10 baits/ha) of vaccine-laden baits distributed on a 300 ha vaccination area. An annual total of 887 raccoons were live-trapped for sedation, physical examination and blood collection for rabies antibody determination; there was no evidence of adverse effects or lesions due to the vaccine. Age and sex distributions, mean body weights, and live-capture histories of raccoons from the vaccination and non-baited control areas were compared. There were no statistically significant differences in survivorship between the baited and non-baited areas, nor between rabies antibody-positive and antibody-negative raccoons from the vaccination area. There was no trend in field mortality that suggested an association with either tetracycline or sulfadimethoxine, used as biomakers, or with vaccine contact determined by antibody status. No gross or histopathologic lesions due to the vaccine were demonstrated among a subsample of live-trapped raccoons collected for gross necropsy, biomarker analysis, histopathologic examination, and V-RG virus isolation attempts. Recovery of V-RG virus was limited to the tonsils of two biomarker-positive, clinically healthy raccoons collected from the vaccination area for postmortem examination on days 2 and 4 following bait distribution. These data reinforce the extensive body of safety data on the V-RG virus and extend it to include field evaluation where vaccine is offered free-choice in abundance, in baits designed to attract free-ranging raccoons, in a relatively simple ecosystem.

Activity patterns of co-occurring populations of Virginia opossums (Didelphis virginiana) and raccoons (Procyon lotor)

Activity patterns of co-occurring populations of Virginia opossums (Didelphis virginiana) and raccoons (Procyon lotor)

Rabies surveillance in the United States during 1995

Summary In 1995, 49 states, the District of Columbia, and Puerto Rico reported 7,877 cases of rabies in nonhuman animals and 4 cases in human beings to the Centers for Disease Control and Prevention. Nearly 92% (7,247 cases) were wild animals, whereas 8% (630 cases) were domestic species. The total number of reported cases decreased 4.2% from that of 1994 (8,230 cases). Most of the decline was the result of 17.1% fewer reported cases of rabies in raccoons in areas of the Northeast, where rabies is now enzootic rather than epizootic. Exceptions to this decline were detected in states where the virus has only recently entered raccoon populations or where ongoing epizootics persist. States experiencing increasing epizootic activity associated with this variant include Maine (3 cases in 1993 to 101 cases in 1995), North Carolina (9 cases in 1990 to 466 cases in 1995), Rhode Island (1 case in 1993 to 324 cases in 1995), and Vermont (45 cases in 1993 to 179 cases in 1995). The raccoon variant of the rabies virus is now present in Alabama, Pennsylvania, Vermont, West Virginia, and all Atlantic Seaboard states from Florida to Maine. In Ohio, this variant, last detected in 1992 as a single case, was again detected in 1996. Epizootics of rabies in foxes in west central Texas and in dogs and coyotes in southern Texas attributable to canine variants continue, with this state reporting 137 rabid foxes, 55 rabid dogs, and 80 of the 83 cases in coyotes during 1995. The number of rabid bats (787) increased by almost 25%, with cases reported by 47 of the 48 contiguous states. Nationally, reported cases of rabies in cattle (136) and cats (288) increased by 22.5 and 7.9%, respectively, whereas cases in dogs (146) decreased by 4.6%. Cats continued to be the domestic animal most frequently reported rabid. The cases of rabies reported in human beings were all caused by viral variants associated with bats. Eighteen states and Puerto Rico reported decreases in rabies in animals in 1995, compared with 28 states and the District of Columbia in 1994. Hawaii was the only state that did not report a case of rabies in 1995.

The introduced raccoon Procyon lotor population in Germany

AbstractThe raccoon Procyon lotor has been naturalised in Germany since 1927. The most dense populations exist in the states Hessia, Northrhine‐Westphalia and Lower Saxony followed by Bavaria, Thuringia, Brandenburg and Mecklenburg‐Vorpommern. By 1985, the raccoon had crossed the borders to Germany's neighbouring countries with the exception of the Danish and Polish borders. The factors limiting population growth are the numbers of suitable resting and breeding places ‐ for which raccoons prefer oaks and beeches ‐ and food supply. The raccoon has not been shown to negatively affect any indigenous wildlife species. In Hessia, plant matter, invertebrates and vertebrates each make up about one third of the diet of the raccoon. Mammals, birds, reptiles, amphibians and fish are important in winter and spring. Invertebrates can be found in considerable amounts all year long, with the maximum percentages found in summer. Plants are the main source of food in autumn. The raccoon has not yet become a problematic species, not even in urban areas. However, cases of rabies in raccoons in Germany have been documented, although seldom compared to fox Vulpes vulpes, marten Martes spp. and deer, e.g Cervus elaphus, Capreolus capreolus and Dama dama. Raccoons are also known as carriers of infectious diseases such as canine distemper, panleucopenia, Aujeszky's disease, canine parvovirus and canine adenovirus. The first case of human infection by a parasite, the ascarid Baylisascaris procyonis, from a pet raccoon was reported in 1991. The extermination of the raccoon population is not considered to be feasible. The yearly hunting bag of raccoons in Germany comprises 2,000–3,000 individuals.

Rabies: An old disease of new importance

Over the last two decades, scientists and health officials have been closely monitoring the exponential rise in rabies among wild raccoon populations in the Middle Atlantic and Northeastern United States. The current spread of the disease in these animals poses a new and potentially increased risk for humans, because of their prevalence in urban and suburban communities, where they are estimated to live in a density of 40 to 50 per square mile. Reasons for the current epizootic are not entirely clear. Some epidemiologists trace the origins to several infested raccoon shipments from Florida to hunting clubs in North Carolina and Virginia during the late 1970s (1). Whatever the reason may be, since 1977 the disease has spread relentlessly northward (Table 1). From the first report of a single rabid

Raccoon rabies: the re-emergence of an epizootic in a densely populated area

Investigation of sporadic or isolated cases of rabies was encouraged in the 1950s by the implementation of a national surveillance system for reporting of rabies cases. Low level enzootic disease was recognized in several wild species during this period, including a small focus of rabies in raccoons in Florida. Phylogenetic analysis of the virus transmitted by rabid raccoons and reconstruction of the early history of raccoon rabies in the United States suggests that rabies was present in these animals long before its recognition by the public health community and that the emergence of raccoon rabies as a major threat to public health was the result of several natural and human-mediated events. In recent years, reports of raccoon-human contact and rabies in raccoons have increased as changes in human demographics and land development have concentrated raccoon populations in urban and suburban settings. In addition to the natural spread of rabies from Florida to raccoon populations in Georgia, Alabama, South Carolina and North Carolina, a separate focus in the northeastern states is believed to have been caused by the translocation of raccoons from the southeast to Virginia and West Virginia. Oral vaccination of wild species may be an important adjunct to traditional rabies control measures in the management of this disease in the future.

Seroepidemiology of Coxiella Burnetii Among Wildlife in Nova Scotia

We used an indirect immunofluorescence assay to determine antibody titers to phase I and phase II Coxiella burnetii antigens in serum samples from a variety of wild animals in Nova Scotia. Forty-nine percent of the hares, 16.5% of the moose, 7.1% of the raccoons, and 1.5% of the white-tailed deer tested had antibodies to phase I antigen. We conclude that there is extensive infection of the hare population by C. burnetii, with lesser degrees of infection of the moose, raccoon, and deer population.

EPIZOOTIOLOGY OF CANINE DISTEMPER IN NEW JERSEY RACCOONS

Seventeen epizootics of canine distemper (CD) involving at least 615 raccoons (Procyon lotor) were identified between 1 September 1977 and 25 March 1991 in New Jersey (USA). Epizootics occurred three times at four year intervals in three areas. Based on this cycling, the wide distribution of CD cases, and their occurrence between epizootics, I propose an enzootic status for CD in New Jersey raccoons. The peak period prevalence of raccoon canine distemper cases occurred at the end of the mating season in March. Another period of CD activity began with increased movements of the young in September. Epizootics were associated with river drainages and other wetlands. Age and sex distribution of raccoons with CD was not significantly different (P > 0.05) from that of an asymptomatic composite sample of four northern New Jersey raccoon populations. Lethargy was the most commonly reported clinical sign in raccoons with alert or aggressive behavior rarely observed.

Tactics for the control of wildlife rabies in Ontario (Canada)

Two different tactics are currently being utilized to control rabies in foxes, skunks and raccoons in Ontario, Canada. The first tactic, which involves live-capturing with cage-traps and vaccinating by intramuscular injection, was successful in immunizing 54%-72% of the skunk and raccoon populations in a 60 km2 area of Toronto, Ontario. This area has been free of rabies for two-and-a-half years. The second tactic, involving the distribution of baits containing modified live-virus (ERA) rabies vaccine, was implemented to control rabies in foxes in both urban and rural areas of Ontario. In Toronto, 50% and 63% of the foxes were vaccinated during 1989 and 1990, respectively. Over the same period, 45% and 61% of the foxes in a 30,000 km2 area of south-eastern Ontario were immunized. Rabies is declining in both of these areas. A contingency plan has been devised to control an epizootic of raccoon rabies which is threatening to invade Ontario from the United States of America.

Influence of Age, Sex, Season and Availability on Den Selection by Raccoons within the Central Basin of Tennessee

-Fifteen raccoons were fitted with radio-transmitters and monitored from March 1987 to May 1988; 1091 locations were classified according to occurrence within three available den types: tree cavities, rock outcroppings and ground burrows. Overall use generally reflected availability of dens, but den use varied across seasons and among raccoons of different age and sex. Rock dens were used most often during winter, especially when temperatures fell below freezing; adult males showed the most frequent and consistent use of rock dens. Ground burrows were consistently used more often by juveniles, especially males, as compared to adults. Use of ground burrows by the raccoon population was greatest during autumn. Females consistently used tree cavities more frequently than males; the greatest disparity occurred during summer and was associated with parturition and rearing of young.

Epizootic of rabies in raccoons in Maryland from 1981 to 1987

Summary The epizootic of rabies in raccoons entered Maryland in 1981 and systematically moved through the state affecting raccoons in all counties except those of the lower Eastern Shore. A precoded surveillance form was provided to all county and city health departments and data were requested for each animal head submitted for testing for the year 1985. The disease persisted and, in 1987, all counties previously reporting rabies in raccoons also had documented cases in other species. The incidence of rabies in raccoons increased in late winter and peaked in March. Most human exposures occurred during daylight hours and in private yards. Agricultural areas were similarly affected by rabid animals. Analysis of vaccination status of animals exposed to rabid animals gave estimations of statewide vaccination rates for dogs (70%) and cats (28%). The danger of rabies in cats was emphasized by the large number of animals exposed by each rabid cat. The spillover of rabies in raccoons to other species persisted in all jurisdiction through 1992, with periodic upsurges of disease at 3- to 4-year intervals as the raccoon population is replenished. Rabies was not diagnosed in any human beings.

Ecologic Relationships of Co-Occurring Populations of Opossums (Didelphis virginiana) and Raccoons (Procyon lotor) in Tennessee

Opossums ( Didelphis virginiana ) and raccoons ( Procyon lotor ) were studied at two sites in Tennessee using mark-recapture techniques. Winter density, relationship of trap success with selected habitat variables, interspecific association, and the degree of mutual habitat utilization were determined. Density of opossums was estimated as one animal/9.9 ha at one site and one animal/44.5 ha at the second location. Abundance of raccoons was estimated as one animal/70.4 ha at one site and one animal/34.5 ha at the other. Number of opossums and raccoons was not significantly correlated with any of the habitat variables measured at either site. Interspecific association values for co-occurring populations were 0.111 and 0.267; these values were not statistically significant and indicated that opossums and raccoons occurred independently of one another in regard to spatial distribution. Both species exhibited a wide range of ecological tolerance for habitat.

Prerequisites for oral immunization of free-ranging raccoons (Procyon lotor) with a recombinant rabies virus vaccine: study site ecology and bait system development.

A model baiting system suitable for the delivery of an oral rabies vaccine to free-ranging raccoons (Procyon lotor) was developed and tested on barrier islands in South Carolina (USA). Features of barrier island physiography and ecology were studied relative to selective bait deployment and site biosecurity. Capture-mark-recapture data were obtained from 228 raccoons. Raccoon density estimates, using a modified census assessment technique, were one raccoon per 1.8 to 2.7 ha. Mean (+/- SE) and range home area estimates of radio-collared raccoons were 84 (+/- 15.6) ha (27 to 176 ha) by a minimum convex polygon method and 138 (+/- 22.8) ha (43 to 241 ha), by a harmonic mean transformation method. Habitat utilization determinations of radio-collared raccoons were conducted to identify study areas to potentially maximize selectivity of bait towards raccoons and to reduce the absolute number of baits deployed. Island raccoons showed a habitat preference for maritime forest, maritime shrub and marsh areas. Additionally, there was no evidence of inter-island or mainland exchange of ear-tagged or radio-collared raccoons. A disease and mortality survey was conducted to identify baseline pathology and incidental lesions in the target raccoon population, prior to actual vaccination initiation. Thirty-eight percent of 30 clinically suspect raccoons sampled had intracytoplasmic eosinophilic inclusions diagnostic of canine distemper; no other lesions suggestive of viral etiologies were found. Serological surveys for raccoon poxvirus and rabies virus antibodies were negative. Antibody titers to canine adenovirus 1 and 2 indicated a moderate level of exposure (approximately 10 to 16%) in the raccoon population. Overall, 93 to 100% of placebo baits were consistently disturbed by 7 days post-bait deployment, and bait acceptance rates by raccoons ranged from 49 to 85%, by using a modular systems approach to select the optimum combination of bait attractant, biomarker, matrix, density, and distribution. These results suggest that a large proportion (up to 85%) of a free-ranging island raccoon population can be selectively and safely targeted, marked and monitored utilizing a proposed oral bait delivery system for recombinant or other rabies vaccines.

Eosinophilic Encephalomyelitis in a Raccoon Experimentally Infected with a Dog Isolate of Rabies Virus

For the past decade, the mid-Atlantic region of the United States has been experiencing an epizootic of rabies in its wild raccoon (Procyon lotor) population. In 1987, there were 965 reported cases of rabid raccoons in this geographical location.* To counteract this epidemic, a genetically engineered vaccinia-rabies glycoprotein (V-RG) oral rabies vaccine has been developed and has been evaluated experimentally in raccoons. 10 It is now awaiting final government approval for field testing. An adult female raccoon used in a control group of animals for the experimental evaluation of the V-RG recombinant virus vaccine was presented to the Laboratory of Large Animal Pathology at the University of Pennsylvania for necropsy. The raccoon had been inoculated intramuscularly with 0.3 ml of rabies virus strain MD5951 (10 5.5 MICLD50), which had been isolated from a dog. 12 On day 12 postinoculation (PI) the raccoon had shown vague neurologic signs and was euthanized on the day of presentation (day 13 PI). Prior to euthanasia, blood samples were obtained for hematology and for the serum neutralization test for rabies antibody. 10

LAND USE ASSOCIATIONS AND CHANGES IN POPULATION INDICES OF URBAN RACCOONS DURING A RABIES EPIZOOTIC

Land use associations and changes in population indices were assessed for an urban population of raccoons (Procyon lotor) in Baltimore, Maryland (USA), from January 1984 to December 1987. Records were examined for 1,458 raccoons trapped alive and removed dead from city streets during, and after, the peak of a rabies epizootic. The distribution of raccoons was associated with single-unit residential areas primarily along the northern and western perimeter of the city. Beginning in March 1985 an ending in May 1987, an epizootic of raccoon rabies spread through Baltimore, ultimately resulting in the identification of 95 rabid raccoons. Within the study interval, annual numbers of trapped raccoons remained stable from 1984 to 1986, before showing a marked decline in 1987. The number of raccoons removed as vehicle mortalities (road-kills) varied little from 1984-1985 but declined in the last 2 yr of study. Numbers of other road-killed species did not decrease concurrently, suggesting a specific decrease in the urban raccoon population. The rabies epizootic, in conjunction with the increased city and private control, appears to have contributed to a decline in the number of raccoons in Baltimore.

Raccoon Populations: Does Human Disturbance Increase Mortality?

Human disturbance is thought to be the major cause of mortality in raccoon (Procyon lotor) populations in North America. To test that hypothesis, characteristics of raccoon populations associated with low human disturbance (no trapping, low vehicular traffic, etc.) and high human disturbance (trapping, moderate vehicular traffic, etc.) were compared in the Manhattan, Kansas area in fall 1986. Estimated annual mortality in the raccoon population exposed to little human disturbance was 26.5%, significantly lower than the 52.5% in the population inhabiting an area of high human disturbance. Counts of placental scars reflected greater reproductive activity in the raccoon population in the highly disturbed area. The higher reproductive activity of raccoons inhabiting the area of high human disturbance may offset the higher mortality experienced by that population. The raccoon (Procyon lotor) is an adaptable mammal with a widespread range in North America (Sanderson, 1987). Stains (1956) presented data that characterized general parameters of raccoon populations in Kansas. Sanderson (1987) concluded from several studies that human activities are the primary causes of mortality in raccoon populations. To test Sanderson's conclusion, the characteristics of a raccoon population inhabiting an area with a large amount of human disturbance were compared to those of a raccoon population exposed to little human disturbance. Specifically, it was hypothesized that the raccoon population in the area with greater human disturbance would have higher mortality than the population experiencing little human disturbance. Herein, are the results of that comparison. MATERIALS AND METHODS Body weight, sex, age, and reproductive data were obtained from raccoons collected from two areas in northeastern Kansas during November and This content downloaded from 157.55.39.173 on Thu, 19 May 2016 06:18:36 UTC All use subject to http://about.jstor.org/terms VOLUME 93, NUMBERS 1-2 23 December 1986. One area was the Fort Riley Military Installation (minimal human activity, few residences, little vehicular traffic, no trapping, no farming, etc.), whereas the other was the rural Manhattan area (higher human activity, farm homes, moderate vehicular traffic, trapping, farming, etc.), 20 km to the northeast. The study areas were on the western edge of the Flint Hills of Kansas. Topography of the region is dominated by rolling prairie intersected with small drainages of intermittent streams. Elevation ranges from 400 to 500 m. Specific boundaries of the study areas are described in Barnes (1987), and vegetation and topography are detailed in Robel et al. (1970) and Klinger (1983). Techniques used to collect raccoons were identical on both study areas, i.e., water sets using steel coil-spring and long-spring leghold traps. Thirtysix raccoons were collected from the Fort Riley area and 92 raccoon carcasses were obtained from furharvesters trapping in the rural Manhattan area. The weight of each raccoon trapped on Fort Riley was determined prior to skinning; body weight data were not recorded for raccoons received from the cooperating furharvesters because the skinned carcasses had dried for various lengths of time before we obtained them. A preliminary determination of sex was made by presence or absence of external genitalia and confirmed by inspection of internal gonads. Age was determined by examining canine root foramina and counting cementum annuli of canine teeth (Grau et al., 1970). Reproductive history was determined by examining uteri of females and counting placental scars. Standard Chi-square, Student's t, F values, and LSD analyses were used to detect significant differences in the data sets at a 0.05 level of probability. Survival of raccoons in the two populations was estimated from trapping results following procedures of Robson and Chapman (1961) as detailed by Eberhardt (1969). For these calculations, we assumed both raccoon populations were static and our trapping efforts provided an unbiased representation of the age classes in each population. Because annual survival and mortality must add up to unity, one minus survival equals mortality. RESULTS AND DISCUSSION Weights of adult raccoons from Fort Riley (8.6 kg) were greater than juveniles (4.1 kg), and adult males (9.8 kg) were heavier than adult females (8.1 kg). Body weights of our adult raccoons were higher than reported in Illinois (Sanderson and Hubert, 1981). Body weight of juvenile male raccoons did not differ from that of juvenile females (Table 1). The proportion of male (39%) raccoons from Fort Riley was not significantly different from the proportion of males (47%) obtained from the rural Manhattan area. Most other studies report higher proportions of male raccoons than females (Sanderson, 1951; Johnson, 1970; Moore and Kennedy, 1985). This is thought to be a reflection of the higher vulnerability of males This content downloaded from 157.55.39.173 on Thu, 19 May 2016 06:18:36 UTC All use subject to http://about.jstor.org/terms 24 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE Table 1. Body weights (kg) of raccoons collected on the Fort Riley Military Installation during November and December, 1986. Category n Body weight (C _+ SE)'

Gastrointestinal Helminths and Protozoa from Two Raccoon Populations in Kansas

A survey in Kansas compared the prevalence of gastrointestinal helminths and protozoa in 2 raccoon (Procyon lotor) populations; a population in a typical rural setting and a relatively undisturbed population on a military reservation. Gastrointestinal tracts of 128 raccoons were examined. Freeze storage of alimentary tracts prevented collection of data on trematode prevalence. Helminth infections other than trematodes included 1 acanthocephalan, 2 cestodes, and 3 nematodes. Helminths were found in all raccoons from the population on the military installation and 96% of those from the rural population. Prevalence of helminths was generally greater in raccoons from the population living in the rural setting. Eimeria spp. and Sarcocystis sp. were also found, whereas Giardia spp. and Cryptosporidium parvum were not.

Vital Statistics and Harvest of an Iowa Raccoon Population

Etude de la reproduction, de la survie et de la dispersion dans une population exploitee de raton laveur entre 1982 et 1986

A study of techniques for the distribution of oral rabies vaccine to wild raccoon populations.

This study evaluates a technique for delivering an oral rabies vaccine to wild raccoon (Procyon lotor) populations. Various baits and attractants were first tested on caged raccoons and baiting trials were then conducted in two distinct physiographic regions of Virginia (USA), the coastal plain and the Piedmont plateau. Raccoon population density studies preceded the field trials. Each polyurethane sponge bait distributed contained approximately 200 mg tetracycline as a tissue biomarker, and was presented in an outer bag with a fish-based attractant. Baits were frozen until used and distributed from an aeroplane throughout two 4-km2 sites in each region. One site received 450 baits/km2 and the other 120 baits/km2. Postbaiting evaluation included the direct observation of baits in the field and the examination of teeth and bone from trapped and hunted animals for evidence of the biomarker. Between 30% and 73% of the captured animals showed evidence of bait consumption. The proportion of animals with evidence of bait uptake changed when areas adjacent to the actual baiting site were included. The percentage of animals taking baits was not related to the density of baits that were distributed.

Use of Earthen Islands by Nesting Ducks in North Dakota

We studied duck nests on 1 natural island and 21 constructed islands on the J. Clark Salyer National Wildlife Refuge (NWR), North Dakota in 1982-83. We found 286 nests of 7 species; mallard (Anas platyrhynchos), gadwall (A. strepera), and blue-winged teal (A. discors) represented >90% of all nests. The mean annual nest density was 8.7/ha with a mean Mayfield-adjusted nest success of 24%. Islands on which the most ducks were produced were 335-1,085 m offshore, surrounded by 150-200 m of open water, and contained tall, dense, brush or forb cover. Three islands with these characteristics held 37% of the nests and produced 55% of total ducklings. Although gadwalls and mallards formed dense nesting concentrations, bluewinged teal showed little nest-clumping behavior or nest cover preferences. Other factors influencing production rates included a seasonal decline in nest success and between-year variability. To be cost effective, islands located in wetlands with large mink (Mustela vison) and raccoon (Procyon lotor) populations should have adequate spatial isolation and/or predator control. J. WILDL. MANAGE. 53(2):411-417 Recruitment rates of ducks in the intensively farmed portion of the prairie pothole region are low (Cowardin et al. 1983) because of declining habitat and concentration of nest and female duck predators (Sargeant and Arnold 1984). Recent efforts to improve waterfowl production have centered on restricting predator access (e.g., electric fencing) (Lokemoen et al. 1982), cover management (e.g., dense nesting cover [DNC], burning, mowing), and construction or improvement of nesting islands. Some island habitats attract large populations of nesting ducks (Drewien and Fredrickson 1970, Browne et al. 1983) and have high nest success due to the reduced impacts of predators (Duebbert 1966, Vermeer 1968). Artificial islands can potentially produce more ducks/unit area than other habitats, but they are expensive to construct and maintain, and in many areas may not improve nest success enough to justify costs (Lokemoen 1985). Several authors have made recommendations concerning island construction (Hammond and Mann 1956, Duebbert 1982), but only recently have they been tested quantitatively (Giroux 1981, Carlsen 1984). Our objectives were to quantitatively assess selected environmental variables that best explain duck nesting use and production for a group of earthen islands, and to recommend ways to improve waterfowl production on islands. We thank R. A. Stomstad and T. B. Brokke for field assistance. We are grateful to D. Walls for logistic support and personnel to assist with field work. Additional support was provided by the University of North Dakota Biology Department and the Institute for Ecological Studies. Special thanks are extended to R. D. Sayler who provided helpful advice and reviewed the manuscript. The final draft benefited from comments made by R. C. Drewein and H. F. Duebbert. This publication is Contribution 8 of the Institute for Ecological Studies, University of North Dakota.