VERTEBRATE PESTS: Resource Availability

On a daily basis, do the words “resource availability” have any special significance to you? In urban pest management programs, the concept of resource availability is essential in many aspects of what we do every day when trying to eliminate or manage vertebrate pests.

In this month’s column, we examine the concept of resource availability and how it affects the everyday pest professional. Many examples could be drawn to do this but I will focus on urban rodent and wildlife examples.

RESOURCES AFFECT CONTROL. Most pest professionals recognize the elemental and essential resources of any urban pest: food, water and shelter.

But these are not the only resources. Warmth or warm locations could be resources. Nesting materials for some mammals and birds could also be resources. Generally, when animals have an abundance of resources they may behave completely different as compared to when those same resources are scarce. Obviously, these behaviors can affect our control efforts dramatically.

Most professionals know how difficult it is to gain control of pest populations in situations where food is readily abundant and easily available to pests (see “Magic Wand” PCT, June 1999). Consider mouse explosions in poorly managed seed warehouses. In such cases, the mice have an unlimited amount of food and shelter in which to thrive and proliferate. Carefully placed rodenticides and snap traps that work exceptionally well only one block away in an auto parts warehouse fail to work in the seed warehouse.

What about water as a resource in such situations? Because water is scarce in seed warehouses, might not water baits then be the best choice for a professional? Well, if this were a rat infestation, the answer is yes. Rats would likely respond to the non-availability of water by eagerly seeking out a water bait. But mice can extract the water they need from the seeds or metabolize their own water. And thus, for mice, whether or not water is readily available within an account is not as critical as for other and typically larger rodents.

Most professionals can also readily attest that when rats have plenty of food available to them, the adult rats of populations often ignore our carefully placed snap traps even when they contain enticing baits. And, attracting rats to bait stations in such situations is often difficult or impossible. But all this changes immediately when the previously available resources of the rats suddenly disappear. Hungry pests no longer have the luxury of ignoring our baits.

DON’T JUMP TO CONCLUSIONS. Unfortunately, sometimes, laypersons and professionals alike will come to conclusions about a control device (a specific brand of trap, bait, etc.) at a particular account based only on the performance of the device at that specific account. Consequently, many devices have been “judged” both positively and negatively over the years because the specific situation and the abundance and availability of resources were not taken into consideration.

For example, clients ask me if repeating multiple catch mouse traps work. I always answer, “It depends on where you need control.” Multiple catch mouse traps work exceptionally well inside properly managed warehouses with a product-free inspection aisle (sanitation line) between the walls and product.

But these same traps, when used inside residential kitchens beneath the sink, often fail to perform. Why? The answer is resource availability. In this case, the resource is harborages and “hidey-holes” for mice.

A mouse entering a new warehouse and running along a wall is obviously exposed and vulnerable, and highly likely to duck into the first hidey-hole (a curiosity trap) it encounters. In a residential kitchen however, the mouse may be well established inside the kitchen sink cabinet base void, the corner of a basement sill plate, etc. In other words, shelter as a resource is not readily available in the warehouse where it is readily available in the house. Thus, the mouse is not as compelled to be “curious” and investigate new holes in the kitchen as it is in the warehouse.

URBAN WILDLIFE. Let’s shift this same principle over to urban wildlife. The concept and the outcomes are often the same. Consider bat houses. Do bat houses work? Sometimes. It depends on the availability of alternative roosting sites. If a local population of bats are displaced from old tree snags due to a development project, bats with no place else to go might move into properly positioned bat houses. If, on the other hand, there is an abundance of alternative harborage sites to the bats (e.g., trees, caves, old buildings, etc.), the bats houses may remain unoccupied for prolonged periods, or they may never be occupied. Those putting up bat houses in these two different scenarios are likely to come to two different conclusions about whether or not bat houses “work.”

Resource availability also plays a significant role when live trapping wildlife. Rabbits, for instance, are easily enticed into a live trap using vegetables during the winter, but are difficult to trap during the summer. Similar cases could be drawn for other species of urban wildlife as well.

What then, is the bottom line of the “resource availability” concept relative to our hard work in attempting to get rid of obnoxious pests in and around human dwellings? Obviously, if we consider our own behaviors as a co-existing species on this planet along with what we consider “obnoxious” pests, humans, in many cases, determine pest resource availability.

It has been said many times: “Sanitation is pest control,” or, “Eighty percent of pest control is sanitation.” Such statements are simply another way of stating if you reduce the availability of the resources, you reduce the likelihood of having pest problems (or the severity of the problems). Easier said than done. Moreover, our behaviors may have little or no impact whatsoever in certain cases.

But often, humans do help to create, exacerbate, as well as correct pest problems through their own behaviors. And although we understand that, most of our clients do not. This is why part of our job is to constantly strive to make IPM information as abundant and readily available to customers as possible. 

The author is president of RMC Pest Management Consulting and can be reached at rcorrigan@pctonline.com.