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Bobby Corrigan

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[Annual Rodent Control Issue] The Science of Urban Rodentology

Annual Rodent Control Issue

This discipline focuses not only on the biology and behavior of common urban rodent species, but also addresses scientific approaches for their management.

August 26, 2014

As is likely obvious, mammalogy is the scientific study of mammals. About 5,419 species of mammals exist and they are classified into about 29 orders. Rodentology is a branch of mammalogy that examines the study of rodents (the word rodent means “gnawing mammal”). The Rodentia is the largest order of mammals and among the most successful. The order Rodentia contains about 2,277 species with a few new species being added every couple of years. This equates to 42 percent of all species of mammals on Earth being a rodent! For comparison, humans belong to the primates within the family Hominidae, which contains but six species, (i.e., only 1 percent of all mammal species).

Urban rodentology is a sub-discipline of rodentology, (as urban entomology is a sub-discipline of general entomology). Urban rodentology focuses not only on the biology and behavior of the rodent species most commonly associated within and impacting cities and towns, but also addresses scientific approaches for their management.
 

A Complex Science.

As with most sciences, urban rodentology is a complex subject. However, the following points present a capsule view of this study:

  • Urban rodentology deals with live, intelligent mammals that are capable of adapting to a wide array of habitats ranging from simple garden sheds to complex skyscrapers; from a suburban kitchen to a super grocery store and so on.
  • Urban rodentology involves multiple rodent species; each species unique.
  • It demands interdisciplinary approaches, from medical significance to understanding the structural components of everyday buildings; from the chemistry of rodenticides to choices of urban landscaping, etc.
  • Because urban rodents are so successful, they are found the world over, in nearly all cities and towns, as well as rural areas and even as feral mammals living away from humans. Urban rodents are found in tropical cities to remote islands off the coast of Alaska; in dry deserts and in wetlands; in coal mines and high up in the Andes.
     

The purpose of this article is to examine more closely the complex but fascinating science of urban rodentology. But more importantly, we want to consider why an understanding of urban rodentology is so essential to pest professionals the world over in ensuring successful (i.e., effective and profitable) management programs of rodent pests.
 

Primary/Secondary Rodents.

Inter-Disciplinary Sciences and Trades Involved With Urban Rodentology

Here is a partial list of scientific disciplines, trades and skills that interface with urban rodentology on an ongoing basis:

  • Mammalogy
  • Ethology (rodent and human)
  • Botany
  • Epidemiology
  • Microbiology
  • Food Safety
  • Population Biology
  • Medical Entomology
  • Parasitology
  • Building Construction and Design
  • Landscape Architecture
  • City Infrastructure
  • Transportation — Construction Elements (especially planes and trains)
  • Pesticide Safety and Training
  • Food Plant Sanitation
  • Livestock Operation
  • Zoological Park Operation


Associated Trades and Skill Sets:

  • Wild animal trapping
  • Structural pest proofing (doors, pipe penetrations, etc.)
  • Keen observing
  • Being an investigator before an applicator

For the purpose of urban rodent management programs, we can divide urban rodent pests into two groups: primary and secondary urban rodents.1 In order of significance, the primary urban rodent species in many parts of the world are: 1) House mouse, Mus musculus; 2) Norway (brown) rat, Rattus norvegicus, and, 3) Roof (black) rat, Rattus rattus. These three species are often referred to as “commensal,” “domestic” and “old world rats and mice.” These rodents belong to the mammalian subfamily, Murinae, after the early Latin word origin of “mur” meaning “mouse.” In this subfamily alone, there are 519 species. Worldwide, within the mouse genus Mus, there are about 38 species, while about 64 species occur within the rat genus Rattus.
 

Formulas for Success.

Our urban rodents are well recognized for being among the most successful of the successful rodents. In fact, the everyday house mouse has been characterized by some scientists as perhaps the second most successful mammal on Earth, right behind Homo sapiens.

So how can we scientifically explain the success of these mammals? There are at least six impressive reasons: 1) a high degree of adaptability to many different structural and infrastructural environments; 2) very fast reproductive rates when resources are plentiful; 3) ability to squeeze families or a local colony into relatively small spaces; 4) some members of local colonies possess highly secretive, elusive behaviors; are active at night; remain alert and immobile per any strange sound, etc. 5) body shapes and colors to avoid detection and predation (i.e., same color as shadows and the ground); capable of scurrying quickly from shadow to shadow; and, 6) intelligence and cognitive abilities. (Among animals, intelligence is difficult to precisely define. However, general indications of intelligence include the ability to learn, matched with behavioral flexibility. Rats, for example, are considered to be highly intelligent, because research has proven they can learn and perform new tasks — an important asset when entering a new building or area for the first time.)
 

Species-specific Successes.

In addition to the six general qualities discussed above, each of the three primary species also possess a number of individual qualities that make them successful.

The House Mouse

  • Often referred to by mammalogists as the “master of adaptation.”
  • Because it is found virtually in all urban and most non-urban environments, R.J. Berry, the famous English biologist, refers to the mouse as a “mammalian weed.”
  • Its small size enables it to nest and hide in areas “right under our noses.” One overlooked napkin box in a restaurant storage closet can harbor 25 mice. Eight mice have been found nesting beneath a hollowed out hard roll in a bakery.
  • Not all mice in a colony are “curious.” Some mice are like rats, they may avoid new objects such as traps and bait boxes completely. All control programs should account for “curious” and non-curious mice.
  • Short home ranges enable the mouse to avoid encountering traps and bait stations if the equipment is not spaced accurately based on detailed inspections.
  • Fast track to sexual maturity when resources are abundant. House mice have been found to be sexually mature in 35 to 40 days in ideal environments (e.g., a supermarket that doesn’t detail clean beneath the gondolas).

     

The Norway Rat

  • Because of its intelligence, mammalogists have referred to it as “diabolically clever.”
  • Research has shown rats are capable of decision making based on previous experience. Just as recently as last month, new research showed that rats can also regret bad decisions.
  • Similar to the house mouse, rats can hugger-mugger their families into a relatively small spaces. It not uncommon to discover an entire family of rats occupying a single concrete hollow block within a partition wall.
  • Rats have adapted to consuming many different food items, or, the same food item over and over as their environment dictates. And should their normal food suddenly become unavailable (i.e., due to a clean-up or removal), city rats can readily shift over and live on the natural foods found in their environment (earthworms, plant seeds, berries, birds and bird’s eggs, acorns, cockroaches, fish and virtually any local mammal, bird, or reptile of smaller size).
  • Rat colonies in urban areas can harbor with their natural homes of earthen burrows (in parks, around structural landscaping); or, they can be readily at home within the walls, floors and ceilings of urban structures of all types. Serious rat infestations commonly develop high up in the ceilings of apartments and office buildings.
  • Depending on the availability of food, water and harborage, the brown rat can establish both short and long home ranges from 25 feet to upwards of 450 radial feet from their nests.
  • Rats have been tracked dispersing relatively long distances of up to five miles round trip in one night and returning successfully to the same nests. These types of feats help explain how rats explore and exploit new neighborhoods where resources are more abundant.
  • Some colony members can, for a complex array of reasons, be highly secretive and remain cautious of new objects (traps, bait stations) or even new arrangements of objects familiar to them within their daily routine. Pest professionals the world over have high regard for the extraordinary efforts it requires to capture the “smart rats” encountered from time to time.

     

The Roof Rat

  • Because the roof rat occupies and is active in the spaces above the typical field of vision of humans and many ground-dwelling prey (cats, dogs, skunks, foxes, coyotes), this species is often among the most elusive of the three urban species.
  • Inside buildings, the roof rat commonly nests up in difficult-to-access spaces of soffits, attics, floor-ceiling voids, leafy nests up in tree tops, dense foliage nests (and therefore, rodent proofing should be a mandatory element of roof rat control services).
  • Roof rats can have extended home ranges upwards of 500 feet (and more), crossing the property lines of several different property owners. This can complicate control programs.
  • Because most roof rats tend to be black in color and their travelways located in dark and shadowy elevated areas, roof rats can remain out-of-sight and out-of -mind — until the numbers increase to a problem level. Roof rats can exist around urban buildings in an on-off pattern. For example, they can interact with building spaces for a few weeks or months at a time, but then leave the building and exist and nest in trees or bushes living on natural foods for weeks or months. This behavior can frustrate both the servicing pest professional and the affected client.

     

Secondary Urban Rodents.

Depending on the location, there are other rodents of significance in and around urban areas. In fact, as urban sprawl continues, any one or more of the secondary urban rodents listed below can emerge as a primary rodent pest species. These rodents also are capable of significantly damaging buildings, contaminating food or posing health threats to humans, their pets and/or their livestock.

  • Tree squirrels (gray, fox, red, flying)
  • Peromyscus mice (deer mice and white-footed mice).
  • Chipmunks
  • Woodchucks
  • Ground squirrels (e.g., California ground squirrel)
  • Pack rats (woodrats)
  • Voles

     

Inter-disciplinary in Scope.

Similar to other aspects of urban pest management, working with urban rodents necessitates involvement in other scientific disciplines as well as other trades and skill sets. Urban rodentology is, for sure, a science but also an art requiring the honed skills of a craftsman.

You can’t provide excellent mouse control, say, in a large commercial office building if you don’t possess a modicum of knowledge about how an office building is put together. This is because city rodents learn, memorize and mark various utility pipes and chases that allow them to move up and down between floors, as well as which are the safest and fastest routes to go from nest to food (e.g., the office building’s coffee break room, or the messiest desks among 100 others). So this involves convincing humans how to maintain desks (altering behavior) so as to not allow mice to proliferate and spread.

If you have ever tried to control roof or Norway rats infesting ceiling areas of a large vertical apartment complex you understand the level of difficulty. Knowing how to read a blueprint to identify various utility chases is more than half the battle. It’s fair to say this kind of knowledge is a prerequisite of being able to gain control.

Moreover, the skill sets of pest proofing and building repairs are essential in being involved in rodent pest management (i.e., weather stripping a door is not the same as pest proofing a door; plugging a small hole to exclude rodents isn’t as simple as stuffing steel wool into a hole or spraying from a can of expanding foam).

Suggested Great Reads in Urban Rodentology

  • Barnett, S.A. 2001. The Story of Rats.Their impact on us and our impact on them. Allen and Unwin. Crows Nest, Australia. 202pp
  • Berry, R.J., 1981a. Town mouse, country mouse: adaptation and adaptability in Mus domesticus. Mamm. Rev. 11:91-136
  • Bronson F.H., 1984. The adaptability of the house mouse. Sci. Amer. 250(3):116-125.

Finally, for those involved in the management of urban rodents, the art and the science of being keenly observant is critical. Greatness in eliminating pest rodents is not about using only great baits and traps, it’s about being a great inspector via keen observational skill as to where to place the baits and traps.

Arthur Conan Doyle wrote in his Sherlock Holmes series, “You must be trained to see what others overlook.” The clever rodents of our cities and towns require nothing less.
 

Summary.

Pause for a moment to consider the professional management of the “every day” house mouse among various urban structures that occur on a typical service route for a pest professional anywhere — i.e., a mouse infestation in the following: supermarket; warehouse; suburban home with a garage and a basement; suburban home next door without garage and basement; an office building with hundreds of cubicles and suspended ceilings; an old restaurant in the old part of the city; an elementary school; and so on. Certainly there is no single template of service for any of these situations. In urban rodentology there aren’t too many “service templates” from which to push the “repeat button.”

Perhaps after reading this, you will be inclined to agree — urban rodentology is as deep a study as is urban entomology, acarology, microbiology or any other of the sciences inter-connected to urban pest management. This science demands site specificity and situational analysis. It is truly a science requiring dedicated, astute and enthusiastic professionals.

 


The author is an urban rodentologist with RMC Pest Management Consulting, Richmond, Ind.


1Depending on the global city or region, other species of rats and mice are also important pests. For example, the Bandicoot and Polynesian rats are important in many parts of Asia and the Pacific Rim countries. Wood mice invade buildings during cold seasons in many European countries and so on.

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