[Annual Rodent Control Issue] Maximizing Hits on Rodent Bait Stations

Figure 1. Rodent bait stations are familiar to all pest professionals. But what factors must be considered to maximize the chances of rodents finding and entering the stations?

Rodent bait stations (see Figure 1 on the right) are a major part of commensal rodent IPM programs the world over. As pest professionals, we install them around and sometimes inside many of our clients’ facilities for two reasons: 1) to provide a preventive measure for any rodents that might approach the building from other areas, and 2) to control a current rodent infestation on the grounds or within the building.

Once installed, we (and our clients) assume three things will happen: 1) the targeted rodents will actually encounter the stations; 2) the rodents will enter the stations; and 3) the rodents will feed on whatever type of bait we’ve placed inside.

Unfortunately it doesn’t always occur like this. The reality is that rodents do not always interact with our installed bait stations. Or, they don’t interact with the stations and their baits quickly enough to achieve what the customer is expecting — a fast solution to their rodent problem.

But why not? What factors are at play that might cause some, or all, of your bait stations to be left unvisited even when you and your customer know there are still rodents active at the site? Are the rodents aware of the stations? Or, did they find the stations, but then disregard them? Or, were the rodents skittish and fearful of these new objects?

The goal of this article is to present an overview of the research associated with rodent biology and behavior as it applies to their interactions with our bait stations. By us better understanding rodents in this regard, we can maximize our chances of rodents finding, entering and feeding on (“hitting”) our bait stations. The principles discussed here apply to both rats and mice, although the Norway rat is emphasized because it is with this rat most of the work has been done.

Behavior Around Bait Stations. Over the past six or seven decades, scientists have gathered insight on the behavior of rodents in response to objects, such as bait boxes, that appear suddenly within their environment. Generally speaking, this behavior is complex and varying (sometimes significantly) from one rodent colony to the next and it depends on several factors. One of the most important is the density of a particular rodent colony. That is, how many rodents are sharing the same resources in a limited area.

Figure 2. Rodents follow trails made by other colony members to locate food and cover. This trail through the turf is a well-used path by rats at night. A bait station could be established at the start of the trail (bottom center of photo).

Think about a rat infestation in a building’s basement, a city lot, an urban park, an unkempt backyard and so forth. What scientists have learned is that rarely are any two rodent infestations exactly alike.

The following discussion, summarized in a numbered list, is a partial selection of the research findings. These findings can help us to implement better and more profitable rodent control services.

Entry into new bait stations. Why do (or why don’t) rats enter our newly installed bait stations?

1. The length of time it takes for rats to enter a new bait station installed in their territory can differ dramatically. Entry might occur in as soon as one day. Or it can take days, weeks or months. Or, they may never investigate your stations. Whether it is sooner or later depends to a large extent on the stability of the environment. For example, for how long has the food, water and shelter remained available and unchanged over time? Have several generations of rodents been able to grow and thrive within the environment? If the location and/or building has been beneficial to the rodent colony and has allowed it to produce and rear its offspring successfully, the rats (at least some) may be skittish of interacting with bait stations, or traps that suddenly appear.
2. Skittishness towards new stations and objects may be particularly strong with the adult females (i.e., breeders).
3. Skittish behavior is stronger towards new bait containers than toward new food.

The role of odors. What do smells have to do with it?

1. The odors associated with individual rodents and the rodent colony in general can play an important role in the feeding, social and reproductive behavior within a colony. These odors (often containing pheromones) also may affect rodents’ responses to our bait stations, traps and baits. In studies with Norway rats on farms, those bait stations installed at specific structural elements on a farm receiving the highest levels of colony activity and thus deposited rats signs (droppings, urine, rub marks, etc.), received the highest number of hits on the stations. What’s more, the social interactions among the rats affected which specific stations the rats visited and which rats within the colony were permitted to feed in the stations.
2. Norway rats often follow trails left by other rats to find food (see Figure 2 above). In part, this is because such trails are laden with the scent of colony and family members.
3. Similarly, whether or not the rats “hit” the bait they find inside a bait station can be affected by the odors previous rats have left in, on or around the station. This is the same behavior in which rodents leave odors associated with the entries to their burrow holes leading to their nests and harborages (see Figure 3 below). Such odors can be present in their droppings, urine and urogenital secretions.

Feeding Behavior. What are rats’ likes and dislikes about their food and eating locations?

1. In general, rats prefer to feed at sites within or close to cover (see Figure 2 on page 85). If good food is discovered in open and exposed areas, they will drag the food to a cover, or to some area in which they fed successfully in the past.
2. In severe infestations, rats have been seen feeding in groups of a dozen or more at the same spot. When a large bait station is installed in the right spot, several members of a family will enter and feed inside the one station.
3. Some scientists believe it is important for adult rodents to have ample space around them while feeding to facilitate consuming enough food. Some adult rodents, for example, might consume more food if they can “sit up” on their haunches, and hold the food with their paws while eating. This might require upwards of 7 inches or more of ceiling space for Norway rats.

Take Away Points. The following 10 recommendations are some take-away points based on the research discussed previously. I also have included what has worked for me over the years when dealing with “finicky” (i.e., tough-to-control) rodents. Together, these tips may help increase the chances of rodents quickly visiting your bait stations. Still, keep in mind that in any infestation there can be unknown forces at play or even previous experiences the rats have learned from that can affect the outcome of any rodent control program.

Figure 3. An active rodent hole. Note the rat hairs stuck to the perimeter of the hole, the droppings nearby the rat’s hole and the “smudge marks” along the edge of the concrete (bottom right). Rats will often leave their “scent” in their feces and within their smudges and secretions to facilitate recognition and familiarity for themselves and other colony members. Of course, it is desirable to have such odors become associated with your bait stations.

1. According to Dr. Peter Cornwell, the renowned urban entomologist, “The success of the treatment depends on the detail of the inspection.” His adage applies very well to rodent control using bait stations. Before installing any bait stations, it is wise from both a service aspect and a business aspect to first analyze the situation. Ask yourself, “Where are the rodents getting their food and water?” Then, assuming earthen burrows are not obvious, “Where is the rodent harborage?” Think about the environmental resources such as warmth, cover (shadows, hard-to-reach narrow pathways), quiet zones, as well as the structural elements the rodents prefer such as corners, utility lines and structural voids.
2. Once you’ve studied the situation, then investigate the affected areas to pinpoint the rodent’s high-activity areas. This is done by observing for active rodent signs (ARS) such as droppings, belly smears, gnaw marks, hairs, obvious rodent trails and the like. In those areas in which the ARS are the most numerous and concentrated (and especially in those areas where the ARS match their environmental resources mentioned previously), think of these areas as the little red balloons you see on a Google map for where to “drop” a bait station.
3. If possible, locate your stations directly next to (not on) the active trails. Missing a colony’s favorite trail by only 10 feet can make the difference in whether or not the rodents will hit your bait stations.
4. Once the stations begin to receive hits, they should not be moved even slightly; nor should any changes be made to the stations for the remainder of the control period.
5. If large stations are warranted, wooden bait stations¹ similar to those used by the U.S. Fish and Wildlife service during the 1960s and ’70s for farm rodent control can be used. I have used these stations repeatedly over the years, with excellent results, when for whatever reasons the rats wouldn’t readily enter the conventional plastic black stations I installed. Wooden stations are simple to build and can be constructed at commercial carpenter shops for reasonable costs.
6. Establishing bait stations in high-activity zones of the rats and then pre-baiting the stations with foods familiar to the rats in that specific area can sometimes cause rodents to overcome or reduce their skittishness towards the new bait stations. Once the presence and location of the stations become familiar to the rat colony, and they readily take to the pre-baiting food, then stations will begin to contain the “colony scent.” The pre-baiting foods can then be removed and replaced with the rodent bait.
7. Inspect for areas that provide rodents cover (low-hanging bushes, behind junk piles and shadowy corners). Once found, look for any ARS that indicate the rodents are active at that specific location, and if so, it’s a good bait station point.
8. Using forceps (always a handy tool for PMPs to carry), collect any fecal pellets found nearby and place a couple of droppings immediately outside both entryways of the stations. Also, place a couple of droppings immediately inside the entry way of the station.²
9. If you are baiting for Norway rats in situations in which the rats have earthen burrows nearby, collect scoops of soil from the main entrance of their burrow system and place this soil into both entry ways of the new bait stations (in the same manner as installing droppings described previously).
10. If scraps of food wrappers, cardboard, small rocks, pieces of lumber or other items are available at the targeted rodent site and contain any obvious rodent markings (urine stains, body smears, hairs) install some of these “familiar items” in and/or around the entry holes and the floor of the stations. Cover as much of the floor with these and other familiar materials as possible (soil, leaves, grasses, etc.). This technique may be especially useful for those rat infestations that have been long-established and have well-established trails.

Summary. Rodent bait stations, of course, are only of value in controlling commensal rodents if rodents encounter, enter and feed upon the baits inside. Our clients aren’t paying to have a line of black boxes surrounding their buildings. They are paying us to provide a service based on our expertise and our ability to analyze their specific situation. So, it’s not about how many stations you install, it’s about the number of bait stations installed into the most effective “rodent spots” around their building or property.

A pest professional who installs 10 bait stations in the best location based on first analyzing each site and reading the signs the colony leaves identifying their specific activity zones will be far more effective than a service person that hurriedly installs 40 bait stations at the same site in a simple perimeter line around a building. This is usually more “linear coverage” than “effective coverage.”

Take the time to design and implement a quality bait station plan based on good inspection and analysis techniques. Getting the rodents to “hit” the stations quickly is the goal right?

We are paid not only for the amount of equipment we use, but for our expertise that guides how we use our equipment. By doing so, we provide what the customer is in fact paying for — the most expedient and safest solution to their rodent problem as is possible.
 

The author is president of RMC Consulting, Richmond, Ind. He can be contacted via e-mail at rcorrigan@giemedia.com.

¹ Dimensions of large wooden bait station using ¼-inch plywood are as such: Length: 24inches, width and height: 8 to10 inches. Entry holes: 2½ inches at each end. Two floor-to-ceiling interior baffles within 3 to 4 inches inside of station (2½-inch access holes in baffles). A lid can be attached using ordinary hinges.
² Utilizing rodent droppings to help jump start new bait stations cannot be practiced on properties that are considered food-handling facilities (food warehouses, food-manufacturing plants, restaurant properties, etc.).