[Vertebrate Pests] Bait Station Reactions

Bait Station Reactions

When you install bait stations into areas infested by brown rats, the reactions to the stations by the rats usually vary from quick visits to the stations to delays in entry ranging from days to even a few months.

 Among pest management technicians the world over, you hear comments such as, “The rats are not interested in the baits because they have other foods,” or, “The rats are afraid of the new bait boxes” (neophobia), or, “The rats are not showing any interest in the stations,” and so forth.

But what actually occurs when we install bait stations into rat active areas? How can we explain the differences in the time it takes for rats to “show interest” in our baits, if they in fact even show any “interest”? Feeding patterns of wild rats in real-world scenarios is oftentimes a complex dynamic. It’s not as simple as rats being “afraid of new things.” In fact, under certain conditions, wild rats exhibit curiosity towards new objects. Let’s take a look.

Feeding learning. Pause for a moment and think about how you learned to feed. Your feeding may have begun with breast milk or with prepared baby formula served from a breast substitute (a baby bottle with a nipple). Over time, your parents started giving you semi-solid baby food out of jars. As you got older, you were served the staple foods your family members were eating daily. And, most of us remember the mild scolding we may have received from our parents instructing us to “Eat that! It’s good for you.”

Well, for rats and some other mammals, learning what is food and, moreover, what is nutritious food for good growth and body health, is not too dissimilar to how humans learn to feed. A lot of research has been done on this subject over the past 50 years and has been published among a wide range of refereed scientific journals. Too, research has been done on how rats react to unfamiliar (novel) foods, as well as to novel objects holding food. Obviously, such research has direct applications to how pest professionals should conduct IPM and baiting programs for rats.

Like us, rats learn to feed beginning when they are pups suckling on their mother until their first forays out on their own. The mother rat’s milk will contain the food chemistry of the foods she has consumed. These “flavors” can be passed along to the suckling young. Then, as the mom rat and the other rats of the nest return from feeding areas outside the nest, they can carry with them various odors, food particles, grease stains, etc., of the foods they sampled (or simply the odors associated with the area in which the food was located).

 Rats feeding in flour or on whole grains such as wheat, oats or corn will have grain particles adhering to their pelage. Similarly, a mom or dad rat or older “sibling” rats feeding on garbage on a city street are likely to have those food odors and particles adhering to their muzzles. As the older rats groom and tend to the newly weaned pups, the young will lick the food fragments off their faces, whiskers, or body. Additionally, fecal pellets of returning rats deposited into the burrow environment will also contain odors (or tastes) of those foods consumed outside the nest.

So, during the first few months of a young rat’s life in the nest and the burrows, they are “conditioned” to the odors of their family’s and possibly, the colony’s foods. When the young rats leave the nest to forage on their own, they are already familiar with their “family’s foods.” And they may now also learn to feed in the same areas and on the same things they find outside the nest as the other rats. Too, the odors of the rats themselves deposited or left in those areas and on objects where the food was gathered assists the rats in recognizing their own colony’s activity in the areas (e.g., body secretions, feces deposited on the base of a garbage cans and Dumpsters, the exterior walls of a grain bins, the back door of a fast food eatery, etc.).

Bait station reactions. You can see the potential applications of this to the differences we note when we install baits and/or bait stations for rats. The materials we use are fairly standard. The responses to our materials vary from complete “disregard,” to aversion, to attraction.

Suppose you install bait stations containing fresh, new bait blocks into areas in which rats are feeding on city garbage cans containing fragments of fried chicken, bagels, mayonnaise, bread, milk, eggs and maybe other human food discards? You may not see rats interact with your bait stations for prolonged periods. But that’s not necessarily because the rats are “neophobic” to the bait stations (i.e., afraid of the new objects). It may simply be due to the stations or the grain blocks being completely different to anything these rats recognize as food. The grain bait blocks may not have any familiar odors to trigger feeding by the rats. Usually, over time, rats begin to leave scent and markings outside the stations, or they make short, testing visits into the stations. They eventually begin to sample the baits. Once this begins to happen, such “food information” is transferred in the manners discussed earlier and we often note the bait stations receiving more and more visits and the baits being fed upon.

 But it doesn’t always take this much time. When we install bait stations containing grain blocks around a grainery where there has been recent clean up, you may notice the stations are visited within just a day or two, and because the grain blocks are relatively similar in food chemistry and odors to the foods of the granary rats, there is minimal lag in the blocks being fed upon.

Affecting Factors. Some of the factors that can affect a rat colony’s reactions to bait stations include:

1.  The environmental conditions of the area to be baited (competing food sources, harborage types)
2. History of the infestation (length of time they have infested)
3. Types of baits and models of bait stations
4. Installation locations (corners, runways, exposed vs. under cover, etc.)
5. Colony age and structure
6. Specifics of bait applications (baits being contaminated with foreign odors or by human contaminants)

Field Tips. Sometimes, we will have little control over the length of time it takes for a group of rats (or at least for the entire rat colony) to interact with new installments of bait stations. Nevertheless there are some tips than can help minimize bait station lags.

• Dovetail sanitation with bait station installation. Some pest professionals argue bait stations should be installed for about one or two weeks prior to any attempts to clean up any area. In this way, the rats can explore and orient themselves to the stations prior to any area shock of all their food sources disappearing. Other pest professionals have noted that with massive clean-up efforts done concurrently with the installation of the stations, the rats are “forced” to investigate the stations and feed on the only food (i.e., the bait) left. Both scenarios are likely to have merit depending on the circumstances (e.g., sometimes, delaying a cleanup is not an option due to local boards of health issuing fines). But the goal is to reduce any foods that will compete with the installed baits relatively soon. In both scenarios, some rats may go foraging beyond their typical home range, searching for the foods and the odors they are most familiar with.
• Install bait stations in established runways, and/or next to vertical walls and surfaces in which it is known the rats travel.
• If vegetation is present, install bait stations under any natural cover within the activity zones of the rats.
• Pay particular attention to corner areas in rat activity zones as rats often rest and visit corners and also carry food to these areas.
• Install stations close to areas where fecal pellets are deposited by the rat colony. If the account is not a food-handling establishment, a few fecal pellets from the immediate area installed into the station’s entry areas may help to encourage rats to visit and investigate the stations (“jump-starting the station”). Quantitative research on this practice would be valuable to pest professionals everywhere.
• Always install fresh and uncontaminated baits (e.g., from insecticide odors, nicotine residues from hands, gloves). Change baits out as needed to keep baits fresh, but in general, its best to change out baits on a need it or not basis of about one month.

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