The changing role of rodenticides and their alternatives in the management of commensal rodents

Rodents cause substantial damage and losses of foodstuffs around the world. They also transmit many diseases to humans and livestock. While various methods are used to reduce damage caused by rodents, rodenticides remain an important tool in the toolbox. However, like all tools, rodenticides have advantages and disadvantages. Several considerations are shaping the future of rodenticide use, including manufacturing and registration costs, concern about toxicity levels and nontarget animal hazards, potential hazards to children, reduced effectiveness of some formulations, and humaneness to the targeted rodents. Many of these disadvantages apply to anticoagulant rodenticides, and their use is being more restricted in numerous settings. This paper discusses rodenticide use but also alternative control methods such as traps, exclusion, habitat management, repellents, and fertility control. While there have been relatively few new developments in rodenticides and other rodent control methods in the last several decades, new formulations and active ingredients are being investigated so that these concerns can be addressed. Some of these new developments and research results are also discussed

Rodents in Agriculture: A Broad Perspective

The largest taxonomic group of mammals is rodents, with over 2200 species known around the world [1]. More recently, it was stated that over 2500 species exist [2]. Many species exist on all continents, with the exception of Antarctica. Rodents have adapted to all ecosystems of the world, including tundra, alpine, temperate forests, grasslands, arid regions, and aquatic systems. They provide many ecosystem functions, including soil aeration and mixing, seed and spore dispersal, vegetation succession, and being an important food source for predatory animals. Some species of rodents are even consumed by people in some parts of the world. Most rodent species are small, secretive, nocturnal, adaptable, and have a keen sense of touch, taste, and smell. Most species have incisors that grow continuously throughout their lifespan, requiring constant gnawing to keep them sharp and at an appropriate length. Many species are active year-round, while some hibernate during the cold winter months, and some estivate during hot and dry summers. Rodent species vary in terms of their reproductive potential, but most are highly prolific, bearing a litter of several young every year with some even producing several litters per year. Some rodent species live relatively long lives (k-selected species), but most live short lives (r-selected species). Some species maintain stable populations, but some show peaks and valleys in population sizes [3]. This occurs with vole (Microtus) populations in the northern hemisphere, which peak every 3–5 years and crash thereafter. This is often related to weather and vegetation conditions, but also predatory pressures [4]. While most rodent species are relatively small and non-descript, they can vary widely in size from mice that weigh 10 g to capybara (Hydrochaerus) which can weigh 70 kg. A much broader background on rodents, including their evolution, morphology, diversity, social organization, behaviour, and ecology, has been reviewed [5]

The changing role of rodenticides and their alternatives in the management of commensal rodents

Rodents cause substantial damage and losses of foodstuffs around the world. They also transmit many diseases to humans and livestock. While various methods are used to reduce damage caused by rodents, rodenticides remain an important tool in the toolbox. However, like all tools, rodenticides have advantages and disadvantages. Several considerations are shaping the future of rodenticide use, including manufacturing and registration costs, concern about toxicity levels and nontarget animal hazards, potential hazards to children, reduced effectiveness of some formulations, and humaneness to the targeted rodents. Many of these disadvantages apply to anticoagulant rodenticides, and their use is being more restricted in numerous settings. This paper discusses rodenticide use but also alternative control methods such as traps, exclusion, habitat management, repellents, and fertility control. While there have been relatively few new developments in rodenticides and other rodent control methods in the last several decades, new formulations and active ingredients are being investigated so that these concerns can be addressed. Some of these new developments and research results are also discussed

Reducing Prairie Dog Populations and Damage by Castration of Dominant Males

Black-tailed prairie dogs (Cynomys ludovicianus) occur widely across the prairie states of North America. They compete with livestock for forage, transmit plague, and damage lawns, landscaping, and property. Interest in non-lethal methods, such as immunocontraception, is growing; however, reductions in the population due to contraception may be offset by increases in survival because adults and yearlings are not subject to the energetic demands of reproduction, and lower densities may increase the amount of resources available to growing offspring. Surgical sterilization provides a means for modeling these effects. Thus, we castrated males prior to the 1998 breeding season to simulate the potential effects of some contraceptives on body mass and survival. During the summer following treatment, the proportion of male and female adults/yearlings and juveniles captured did not differ between treatment and control coteries; however, the proportion of adults and yearlings captured decreased with later trapping periods. Hence we cannot recommend castration of dominant males to reduce colony expansion and damage by prairie dogs. Other methods of fertility control (GonaCon and diazacon) have shown more promise in prairie dogs

Black Bear Use of Forest Roads in Western Washington

Radiolocations (108) of 20 black bears were used to assess use or avoidance of 3 forest road types in western Washington. Distances of bears to each type of road were compared to distances of 108 random points using t-tests. Females and males avoided 2-lane roads, while only males avoided 1-lane roads, the most common road type in the area. Females, but not males, were located closer to overgrown, spur roads than expected. This road type has substantial cover of grasses, forbs, and berry-producing shrubs along with protective tree cover. This situation may provide easy travel for females along with security cover and a relatively abundant source of high-energy foods that could favor high reproductive success. It also suggests that 1-lane roads and overgrown roads are the best places to locate supplemental feeding stations aimed at providing nutrition to female bears in the spring

Perspectives on Existing and Potential New Alternatives to Anticoagulant Rodenticides and the Implications for Integrated Pest Management

Comprising over 1400 species worldwide, rodents are the largest taxonomic group of mammals (Nowak 1999). Rodent use of habitats is extensive and varied. Most rodent species are relatively small, secretive, prolific, adaptable, and have continuously growing incisors which require constant eroding by gnawing. Rodents are known for their high reproductive potential; however, there is much variability between species as to the age at first reproduction, size of litters, and the number of litters per year. All rodent species have ecological, scientific, social, and/or economic values. They recycle nutrients, aerate soils, distribute seeds and spores, and affect plant succession. Some provide meat and furs for people. Several species are used in large numbers in medical research. Additionally, they provide an important prey base for many species of predatory animals

Rodent outbreaks in North America

Fluctuations in rodent population densities in North America are a reality. Our understanding of the factors causing such fluctuations is incomplete; therefore, it is important to monitor populations to increase our understanding of natural wildlife communities so as to avoid substantial damage to agriculture, forestry, and urban infrastructures, and to prevent rodent-borne disease transmission to humans. There is a need to establish integrated pest management programs in which monitoring, preventive cultural practices, and various control methods (mechanical, physical, biological, and chemical) are strategically coordinated to maintain rodent population densities at acceptable pest levels

Rodent outbreaks in North America

Fluctuations in rodent population densities in North America are a reality. Our understanding of the factors causing such fluctuations is incomplete; therefore, it is important to monitor populations to increase our understanding of natural wildlife communities so as to avoid substantial damage to agriculture, forestry, and urban infrastructures, and to prevent rodent-borne disease transmission to humans. There is a need to establish integrated pest management programs in which monitoring, preventive cultural practices, and various control methods (mechanical, physical, biological, and chemical) are strategically coordinated to maintain rodent population densities at acceptable pest levels

STATUS OF COYOTES AND COYOTE DEPREDATIONS IN PENNSYLVANIA

The coyote (Canis latrans) population in Pennsylvania has grown in the last several decades to about4,000. It continues to grow, despite a known annual harvest of more than 850 animals. There is a growing concern about the effects of coyotes on game and livestock populations. We discuss known and potential coyote-human conflicts in Pennsylvania and propose a program of depredation prevention and control. To be successful, the program requires cooperation, funding, research, educational materials, and training workshops

Black Bear Damage to Forest Stands in Western Washington

Cambium-feeding behavior by black bears (Ursus americanus), or bear damage, is a major reforestation problem in the Pacific Northwest. Historically, studies have measured the cumulative effects of damage over time, but few have viewed damage in the frame of one season. Bear damage occurring in 1996 was surveyed in areas of radio-marked bears in western Washington. Fresh damage occurred on 48% of bear location plots (n = 96). Douglas-fir (Pseudotsuga menziesii) (69%), western hemlock (Tsuga heterophylla) (19%), and Pacific silverfir (Abies amabilis) (10%) with a mean dbh of 25.1, 29.5, and 30.7cm, respectively, were most frequently damaged. Random plots were surveyed from mid-July to mid-August to measure habitat availability. Stand and site variables were measured on freshly damaged bear location plots, random plots, and non-damaged bear location plots. This study identified several variables that make forest stands vulnerable to bear damage: conifer dbh, conifer density, stand age, and canopy cover. Awareness of such stand characteristics can assist natural resource managers with animal damage prevention and control programs