Self-resetting rat traps are powerful tools for conservation — but protecting non-target wildlife is equally important. After rare bird fatalities were documented in Hawaii and New Zealand, researchers launched a detailed experimental study to understand how trap excluders and mounting height influence bird safety on Goodnature A24 traps.
The goal was not only to reduce bird access to traps, but also to preserve effective rodent control. The research combined controlled aviary trials with barrier testing to identify the physical limits of bird entry and inform future excluder design. :contentReference[oaicite:1]{index=1}
Why Non-Target Protection Matters
Goodnature A24 traps are widely used in conservation programs because they can operate continuously with minimal servicing. However, the trap’s cylindrical entrance means that small birds capable of fitting into the opening may be at risk if no protective excluder is installed.
While non-target bird incidents remain rare, even a few events — especially involving endangered species — justify proactive design improvements and best-practice deployment guidelines.
What the Researchers Tested
Researchers evaluated bird interaction with disarmed A24 traps using three representative species:
- Red-winged blackbirds
- European starlings
- Puaiohi (an endangered Hawaiian forest bird)
The experiments focused on three core variables:
- Barrier gap height – how small a space birds can physically pass beneath.
- Excluder type – plastic Goodnature excluders vs. homemade metal mesh excluders.
- Trap height placement – low mounting versus elevated mounting.
Birds were motivated using preferred food rewards to determine whether they could physically reach the trap trigger area under different configurations.
Key Finding #1: Birds Can Pass Through Surprisingly Small Gaps
Barrier trials showed that:
- European starlings could pass under gaps as small as ~1.9 cm.
- Red-winged blackbirds could pass under gaps down to ~2.9 cm.
This establishes a realistic physical threshold for future excluder designs. Any opening larger than these dimensions risks allowing small birds to enter. These measurements also align with the physical ability of rats and mice to pass through small openings, meaning properly designed barriers can exclude birds while still allowing rodent access.
Key Finding #2: Excluders Significantly Reduced Bird Entry
When no excluder was installed, all three bird species were capable of entering the trap at both low and high mounting heights.
When excluders were installed:
- Both plastic and metal excluders prevented entry for more than 75–87% of blackbirds.
- Starlings were harder to exclude, but overall entry rates remained low.
- Puaiohi entry was substantially reduced compared to traps without excluders.
Plastic excluders performed as well as — and in some cases better than — metal mesh excluders, without the same level of rodent avoidance observed with long metal blockers in earlier field studies.
Key Finding #3: Raising Trap Height Alone Does Not Eliminate Risk
Elevating traps reduced access for some birds, but did not reliably prevent all entry — especially for agile species capable of jumping or climbing.
Sample sizes for high-mounted traps were limited, and results were inconsistent. Researchers caution against relying solely on trap elevation as a safety strategy.
In some cases, elevating traps may actually expose additional bird species that normally do not forage on the ground.
Key Finding #4: No Single Design Achieved 100% Exclusion
Although excluders significantly reduced bird access, none of the tested configurations completely eliminated entry for all species under all conditions.
This highlights the biological reality that small birds and rodents overlap in size and agility. Designing a perfect exclusion system without impacting rodent access requires careful engineering tradeoffs.
Researchers proposed a future excluder concept that uses a wider barrier footprint with a precisely controlled gap height to allow rodent passage while preventing birds and allowing carcasses to clear without clogging.
Practical Takeaways for Trap Deployment
Based on the study results:
- Excluders should be used in areas where sensitive bird species are present.
- Plastic excluders positioned approximately 0–2 cm above ground provide strong protection with minimal performance impact.
- Metal mesh excluders may reduce rodent entry more than plastic designs.
- Trap placement near natural rodent travel corridors improves success.
- Managers must balance wildlife protection with control efficacy based on local conditions.
No single configuration is perfect for every environment. Responsible deployment requires adapting to site-specific wildlife behavior and risk profiles.
Final Takeaway
This study confirms that Goodnature A24 traps can be operated more safely for non-target birds through thoughtful use of excluders and informed placement strategies.
It also reinforces that continuous refinement, monitoring, and science-driven engineering remain essential for responsible pest control at scale.
Citation:
Shiels AB, Crampton LH, Spock DR, Greggor AL, Earnest K, Berry L, Masuda B (2022). Testing Goodnature A24 rat trap excluders and trap height placement to prevent non-target bird mortality. Management of Biological Invasions 13 (in press).
