Strategies For Urban Rodent Control

Urban and suburban rodent problems appear to be increasing nationwide and business owners, residents and politicians are all wondering why. There are several contributing factors: infrastructure is aging, the number of food establishments (restaurants) is increasing, congestion is becoming greater, refuse containment commonly is inadequate (plastic bags) and urban sprawl is occurring at a rapid rate. At the same time, leadership and funding for commensal rodent control has been declining for 20 years.

Commensal rodents are "indicator species" of environmental integrity or decay. Their presence reflects a quality-of-life issue that can be described in terms of economics, public health or aesthetics. However, the focus should not be on the existence of the rat or mouse, but rather why the rodent exists at the particular location. Such an assessment begins the process of shifting from a reactionary approach to a proactive (preventive) plan.

Today in the United States, rodent control at the municipal level typically consists of an assortment of efforts by pest control companies, municipal workers and homeowners. If a municipality has a program, it generally is implemented in a limited or disjointed (piecemeal) fashion and commonly without effective staffing, planning, funding or technical skills. The goal when designing an effective rodent control program is to establish a comprehensive and sustainable plan. Municipalities (and others) commonly focus on short-term (political "quick-fix") efforts without looking forward and thus remain in a cyclical pattern of intensive efforts followed by inattention. Within a few weeks or months of reduced efforts, rat outbreaks can occur and municipalities (or building owners) once again respond in a reactionary way. Over time, this cyclical approach is expensive, inefficient and reduces the ability to sustain public participation. Programs that focus solely on poison baiting or trapping, or that are implemented for political reasons, are destined to waste money and fail.

HISTORY. The future success of rodent control can be best assured by understanding the history and politics of it. The "Modern Rodent Control Era" began with World War II, since there was concern about food protection and urban destruction. Research in the 1940s was centered at Johns Hopkins University in Baltimore, led by Dr. David E. Davis. That team of researchers evaluated and documented for the first time numerous aspects of the behavior and ecology of Norway rats (Rattus norvegicus). Work by Davis and his colleagues subsequently became the foundation for future rodent control programs and strategies worldwide.

By the late 1950s, the research program at Johns Hopkins University had ended; however, the important principles of rodent control and rat behavior had been established. For example, the researchers were able to show that rat populations grew at a relatively predictable rate, following a logistical growth curve (a sigmoid or s-shaped curve). Understanding of that mathematical expression could be used to help strategically manage rodent control programs.

The sigmoid curve (Fig. 1a) shows how populations change in size over time. The rate of population change is initially slow but becomes rapid once the population passes an inflection point in the growth curve. Population growth then slows (plateaus) as the population reaches carrying capacity, which is the maximum number of animals that can be supported by available food and harborage. When carrying capacity is lowered through good sanitation practices (Fig. 1b), the rate of population growth is slowed, the s-curve flattens and opportunity to manage the rodent population is greatly improved.

Davis sought to demonstrate these principles in the field. Rat numbers were monitored in a Baltimore neighborhood during poisoning campaigns in 1943-47 and subsequently during an intensive sanitation program in 1947-1950 (Fig. 2). Numbers were substantially lower during the sanitation period, except in late 1948, apparently because of a strike by refuse workers. The re-sults demonstrated that rat populations could be managed through habitat modification.

After the Johns Hopkins program ended, Dr. William Jackson, a student of Dr. Davis, continued the legacy of research at Bowling Green State University in Ohio. During the 1960s to 1980s, that work included rodent behavior but also rodenticide development, genetic resistance to anticoagulants and other technical aspects of rodent control.

During that same time period the federal government was actively involved supporting research, developing education and training materials and providing millions of dollars annually to municipalities for control programs. For example, Washington, D.C., alone received $1.1 million in 1968. However, by the mid-1980s, federal involvement and technical leadership ended and municipalities were left on their own to deal with the problem. At about the same time, the research program at Bowling Green State University (and a parallel one at the University of California, Davis) ended with faculty retirements.

Today, most states and municipalities have limited understanding of commensal rodent control or expertise in program development. Unfortunately, it is rare to find a mammalogist interested in commensal rodents or urban environments, and thus by default, entomologists commonly have become sources of information. University research and federal leadership in the United States is largely non-existent at this time.

STRATEGY. The term "strategy," when used in context of pest control, should commit the user to a comprehensive or holistic approach that is tailored to the particular situation. It also reflects the intent to win. A dictionary definition of strategy reads: "the science and art of employing the political, economic, psychological and technical resources to meet an enemy in combat with the greatest advantage." At the same time that a pest control program must have a strategy, realize that rodents have a "life-history strategy" that is a combination of behaviors and traits that allow them to leave offspring (genetically succeed). The program strategy must be designed and implemented to overcome that life-history strategy (high reproductive rate, adaptive behaviors, colonizing ability), while using more than just technical resources.

In wildlife management for game species, the strategy is to sustain (conserve) the population while implementing annual harvesting through hunting/trapping. Habitats are protected or enhanced as part of game management. In contrast, rodent control is not about establishing a sustainable yield of animals. It is about sustainable reduction in rodent numbers through elimination (destruction) of habitat features that are important to commensal rats and mice. Many rodent control programs are simply a haphazard harvesting of the "standing crop" of rodents, just as a farmer harvests a hay crop multiple times each year.

It is most economical (and strategic) to manage a rodent population at the low end of the sigmoid growth curve under reduced carrying capacity (Fig. 1). At the low end of the curve, a population shows modest change over time. In contrast, the population can increase rapidly during the same amount of time farther along the growth curve. Simply stated, it is much more work to control a rodent population once it is reproducing at the rate reflected by the steep part of the sigmoid curve. Intensive monitoring for rodent activity and continued environmental management when a population is low is the best economic strategy for minimizing rodent impacts and long-term costs.

Many efforts to control rodents simply reduce the population from carrying capacity to a level at the mid-point of the sigmoid curve. The extra efforts to solve the problem are not deployed, assuring a wasted use of resources. The population begins a rapid reproductive surge under reduced competition and may actually reach numbers greater than before, within three to six months.

PROGRAMS. Rodent control is a topic that requires broad understanding of urban and suburban complexities. This includes the behavior of people; aesthetic and economic aspects of rodent impacts; political agendas; engineering and repair of infrastructure; codes and regulations; and sanitation measures.

The urban-suburban gradient is becoming increasingly blurred as suburbia of the 1950s ages and is engulfed by urbanization. The primary difference between urban and suburban rodent control is the intensity resulting from differences in the abundance of structures (buildings, utilities) and human population density (sanitation issues). The basic program elements, however, apply to both environments.

For any program, whether a single location or an entire city, there must be an "action plan" with an inherent IPM strategy. The plan must be flexible and be designed to solve the problem rather than to delay its resurgence. The primary focus must be on communication, partnering, teamwork and scheduling rather than blame casting.

The key to an effective municipal program is centralized management, leadership and accountability. Work tasks must be defined, contract specifications written, competent and skilled personnel hired and administrative principles established. Administration is rarely mentioned as a component of IPM, but it is in fact the most important aspect. The science of rodent control has been well established, however the failure of programs appears most evident because of a lack of competent administrators, training and planning.

Numerous groups and agencies must participate for a municipal program to be successful, but one group (or person) must ultimately be accountable for program coordination. Municipal participants should include the Water and Sewer Authority, Public Works Department, Parks and Recreation Department, Planning and Zoning, Community Liaisons, Food Protection Division, Housing Authority, Solid Waste Division, Health Department, Code Enforcement and others. Private industry must be part of the extended team, including the pest control industry, waste haulers and professional associations (building managers, restaurants). Community activists and groups must be recruited and a grass-roots capability established for program sustainability.

KEY PROGRAM ELEMENTS. There are numerous and interrelated elements of an urban (or suburban) rodent control program. Examples are described below.

• Initiate education and outreach using diverse, creative and quality (non-bureaucratic) materials to change the behavior of people. Use a marketing style and target residents and businesses. Public participation is key to management of program costs. The more the public participates, the fewer problems requiring chronic resolution and expenditures. Commensal rodent control is not a spectator sport and community outreach must be far-reaching and credible.

• Establish up-to-date codes that identify requirements for sanitary conditions and structural maintenance. Topics can include keeping residential and commercial properties free of rats and mice, debris, weeds, junk and abandoned cars. Codes also should include proper storage and disposal of refuse, garbage and grease. There must be written procedures for enforcement, including hearings and a schedule of fines. Enforcement is the ultimate public education tool and must be implemented professionally for the program to succeed. Enforcement must include the ability to collect fines and the potential to bring criminal charges for serious offenses (e.g., illegal dumping or refusing to close a rat-infested restaurant).

• Effectively target trapping and baiting campaigns so they are complimentary to other program elements. Avoid declaring victory when a carcass is found; redirect the enthusiasm to environmental modifications and intensive monitoring that ensures population control to a non-detectable level. Widespread and random baiting alone will not achieve a sustainable result. Divide baiting into an initial strategy to achieve control and a maintenance strategy to intensely monitor and protect against re-colonization. Consider both surface and subsurface (sewers, utilities) environments.

• Enhance sanitation through education and enforcement. Ensure that refuse containers are not accessible to rats and mice and that the proper types of containers and compactors are used and properly maintained. Use neighborhood cleanup days to enlist public participation and establish the capacity to cleanup abandoned properties and lots. Inadequate containment of grease and illegal disposal of it into sewerage systems can be a major contributor to rat problems. Emphasis on the use of grease traps and rat-proof grease containers or storage sheds must be established.

• Ensure effective inspection, monitoring and data management. Use standardized urban survey methods and mapping. A rodent control program can not be sustained or cost-effectively implemented without the ability to track events, target control resources to the need, or demonstrate accomplishments to the public and policy makers. Management of a program requires the capacity for quick assessment and adjustments to match environmental conditions. Strategic elements of a program must be integrated based on field data and predictions of population trends and future needs. A predictive (economical) program keeps resources and personnel ahead of rodent population growth and sanitation problems.

• Include infrastructure design and land-use planning as a critical front-end method of rodent control. This includes planning urban environments so they are not intrinsically conducive to rodent activity. For example, restaurants should have adequate storage space for refuse containment and a sanitation plan before being permitted to operate. Landscape designs should include rodent-proofing principles; for example, massed plantings of needled evergreens should not be located near potential food sources and refuse containers and benches should not be placed next to dense shrubbery.

Construction and demolition are becoming increasingly common with aging infrastructure and urban sprawl. Major construction projects should be required to have rodent control and sanitation programs that begin before construction mobilization and that continue until construction is finished. Maintenance of sidewalks, sewerage systems and other structures is essential for rodent control and must be factored as part of a comprehensive program. This means working with engineers, architects and maintenance personnel.

CONCLUSION. The need for effective rodent control programs will become even greater in the 21st century with expectations of residents and businesses for quality-of-life improvements and effective public health management. However, substantial changes must be made in the way that programs are designed and managed, whether for a single building or an entire city.

Reactionary approaches must be replaced with proactive (preventive) programs in which environmental management is the central theme. The environmental and political arenas of the urban environment are complex and both subjects must be mastered for successful implementation of a rodent control program.