PPC118 | Technical

Bait stations have long been a cornerstone of rodent control, providing a secure, tamper-resistant method for delivering rodenticides. However, as this study highlights, the effectiveness of these stations often depends on rat behaviour.

Surprisingly, roof rats don’t always enter bait stations they encounter - a phenomenon that reduces the overall success of control programmes. In this research, only 31% of bait stations were entered during a 21-night trial, even though rats were frequently detected around the bait station.

Implications for rodenticide restrictions With increasing regulatory restrictions on rodenticides, including California’s Assembly Bill 1788 and 2552, which limits the use of all anticoagulant rodenticides, PMPs are operating with a shrinking toolbox.

In the UK, you’ve already seen stricter restrictions on glue trap use, with a ban in Wales and licensing in England. There’s nothing to say that rodenticides aren’t next.

This study underscores the need to optimise existing tools, such as bait stations, to remain effective under these constraints. Supplemental baiting and tracking tunnels represent practical adaptations that can boost success without increasing risks to non-target species.

"Observations from this study revealed multiple instances of rats hoarding significant amounts of bait, underscoring the need to account for this behaviour."

Station design

The study evaluated three commercially available bait stations of different designs: EZ-Secured, Rodent Rock, and Big Snap-E Cover. These stations were placed in urban residential yards in southern California and monitored using game cameras.

Each design offered unique features - the Snap-E Cover, for instance, included large entrance holes that allowed rats to see through the station and view the bait from the exterior, while the EZ-Secured and Rock stations featured enclosed designs.

Despite this, the study found no significant differences in discovery or entry rates among the designs.

While station design may not drastically influence initial attraction, it can affect practical outcomes. For instance, the EZ-Secured station, weighted with a cement block, proved more resistant to disturbances by larger non-target animals like opossums, compared to lighter designs.

Additionally, the enclosed designs of the EZ-Secured and Rock stations may provide a sense of security for rats, as previous research shows that opaque or covered stations are often preferred over more open ones.

These findings suggest that PMPs should select bait stations for their suitability to the specific environment and target species, as well as their tamper-resistant features.

Scent lures: mixed results Another tested strategy involved adding peanut butter and chocolate-scented lures inside bait stations. While scented stations saw slightly higher entry rates than unscented ones, the difference was not significant. This suggests that while scent lures may work in specific contexts, they are not a universal solution. PMPs might find better success using lures derived from rat pheromones or other conspecific scents, as previous studies have shown promising results with these attractants.

Supplemental baiting: A game-changer

Perhaps the most actionable insight from this study is the effectiveness of supplemental baiting. During trials, non-toxic bait placed around stations increased both the likelihood of station entry and the amount of bait consumed.

This approach mirrors pre-baiting practices commonly used in rodent trapping, which familiarise rodents with traps before they are activated. PMPs should consider surrounding stations with non-toxic supplemental bait to enhance rodenticide efficacy and reduce time spent on prolonged control efforts.

Roof rats are notoriously neophobic, meaning they are wary of new objects in their environment. This innate caution often leads them to avoid bait stations altogether.

The research demonstrated that supplemental bait scattered around stations effectively reduced this avoidance. By familiarising rats with the bait’s presence, PMPs can potentially increase the chances of station entry and bait consumption.

Non-target species, such as opossums (non-native) and woodrats (native), occasionally entered bait stations during the trials. Interestingly, juvenile opossums, small enough to fit through station entrances, were observed more frequently shortly after the species’ breeding season.

While neither of these species are present in the UK, species of comparable size may behave similarly, which highlights the importance of timing in rodenticide applications to minimise risks to non-target animals.

Bait hoarding and tracking tunnels

Observations from this study, revealed multiple instances of rats hoarding significant amounts of bait, underscoring the need to account for this behaviour in rodent control efforts. 

Roof rats exhibited hoarding behaviour, often removing bait from stations and storing it in secluded locations, such as under patio furniture or other hidden areas. This behaviour can complicate pest management strategies as it reduces bait availability at the intended site and may lead to unintended rodenticide exposure in other areas.

In addition to bait stations, the study tested tracking tunnels as a method to estimate rat activity and abundance. These tunnels, paired with non-toxic bait and ink tracking pads that record rat footprints, provided activity and abundance indices comparable to those from game cameras and traps. 

For PMPs, tracking tunnels could be an economical and effective tool for pre-treatment assessments, helping to identify areas of high rat activity before deploying control measures.

Practical recommendations

Deploy supplemental bait: 
Scatter non-toxic bait around rodenticide stations to reduce neophobia and increase station visitation.

Monitor with tracking tunnels: 
Use tracking tunnels to assess rat activity and prioritise high-activity areas for bait 
station placement.

Consider scent lures sparingly: 
While not universally effective, scent lures may enhance station entry in certain contexts. Experiment with pheromone-based attractants for better results.

Account for seasonality: 
Be aware of seasonal patterns in non-target species activity and adjust baiting programmes accordingly.

Emphasise training: 
Educate clients about the importance of proper bait station placement and maintenance to maximise efficacy.

Roof rats remain a formidable challenge in many urban and suburban settings and leveraging insights from behavioural research can help PMPs fine-tune their strategies to improve management outcomes.

Incorporating practices, like supplemental baiting and tracking tunnel monitoring, can make existing tools more effective, ensuring that PMPs stay ahead of these elusive pests. 

For PMPs in the UK, these findings are particularly valuable, as they offer strategies to adapt rodent management practices in light of similar regulatory pressures and urban challenges. 

It may be that these insights are also adaptable to species like Norway rats, but these rats are rarely encountered in the area the study was conducted. 

Given the global distribution of roof rats and their impact on human and natural environments, adopting these evidence-based approaches will enhance pest management efforts worldwide, helping PMPs maintain high standards of control and safety in diverse settings.

The authors would like to thank the Pest Management Foundation for funding and acknowledge the support of VM products, Liphatech Inc., Kness, and J.T Eaton.