Self-resetting rat traps play a critical role in protecting endangered wildlife — but what happens if non-target animals accidentally interact with them? After several rare bird fatalities were documented in Hawaii, researchers launched a multi-year field study to determine whether simple trap modifications could reduce bird risk without compromising rodent control.
The study tested different lure types, trap heights, and blocker devices on hundreds of Goodnature A24 traps across Kauai and Oahu, measuring how each change affected rat kill rates under real-world field conditions. :contentReference[oaicite:0]{index=0}
Why Non-Target Safety Matters in Conservation Trapping
Hawaii has lost more than half of its native bird species since human arrival, largely due to invasive predators like rats. A24 traps have been widely deployed since 2014 to suppress rat populations in sensitive forest habitats.
Although non-target captures are extremely rare, several passerine birds were found killed by A24 traps during 2018–2019. Even isolated incidents prompted immediate investigation — because conservation programs must balance effectiveness with responsibility.
Researchers set out to answer a practical question: Can trap design be modified to discourage birds while still maintaining strong rat suppression?
The Modifications Tested
Across three field experiments, researchers evaluated four main variables:
- Trap height: Standard mounting (~12 cm above ground) versus elevated mounting (50 cm).
- Blockers: Plastic black blockers and metal mesh blockers designed to prevent bird entry.
- Lure type: Static chocolate lure versus automatic lure pump systems.
- Lure flavor: Chocolate versus cinnamon-infused lure.
Trap performance was measured using digital kill counters and carcass recovery, with data collected across multiple seasons and habitat types including streams, terraces, and upland forest. :contentReference[oaicite:1]{index=1}
Key Finding #1: Trap Height Did Not Affect Rat Kill Rates
Raising traps from the standard 12 cm to 50 cm above ground had no statistically significant impact on rat kill rates.
Black rats are excellent climbers and readily accessed elevated traps. While height adjustments were initially considered as a way to limit bird access, later observations suggested birds could still reach elevated traps under certain conditions.
As a result, increasing trap height alone does not meaningfully improve bird safety and does not enhance rodent control.
Key Finding #2: Cinnamon Lure Slightly Reduced Kill Rates
Cinnamon was tested as a potential bird deterrent based on earlier behavioral research. While cinnamon did not significantly repel rats, kill rates were slightly lower compared to standard chocolate lure.
The reduction was small but measurable, suggesting cinnamon may not be ideal where maximum trap efficiency is required.
Automatic lure pumps performed similarly to static lure bottles in these trials, though sample sizes were limited during certain seasons.
Key Finding #3: Blocker Design Matters
Blockers had the greatest impact on trap performance — and not all blockers performed equally.
Metal mesh blockers:
- Significantly reduced rat kill rates.
- Rats strongly avoided traps equipped with long metal blockers.
- Many metal-blocked traps recorded zero kills.
Plastic black blockers (Goodnature design):
- Caused only a slight reduction in kill rates.
- Did not significantly deter rats.
- Successfully reduced bird access in separate observational trials.
This makes black plastic blockers the most viable safety modification when bird exposure is a concern.
Landscape and Season Were Bigger Drivers Than Hardware
Interestingly, habitat position had a stronger influence on kill rates than most hardware changes.
- Traps near streams and terraces consistently recorded higher kill rates than upland locations.
- Kill rates varied seasonally, often peaking in fall and spring.
This suggests that trap placement and seasonal timing may have a larger impact on success than minor configuration changes.
What This Means for Responsible Trap Deployment
Practical takeaways from the study:
- Black plastic blockers can improve non-target safety without major performance loss.
- Metal blockers significantly reduce effectiveness and should be avoided.
- Trap height adjustments alone do not meaningfully improve safety.
- Standard chocolate lure remains the most reliable option.
- Placement near rodent travel corridors improves results.
In conservation environments where bird exposure exists, blocker use should be paired with thoughtful placement and monitoring rather than relying on any single modification.
Final Takeaway
This study demonstrates that Goodnature A24 traps can be modified to improve non-target safety while preserving effective rat control — when the right modifications are used.
Rather than compromising performance, thoughtful design choices allow conservation teams and land managers to operate responsibly, transparently, and effectively.
Citation:
Crampton LH, Reeves MK, Bogardus T, Gallerani EM, Hite J, Winter TA, Shiels AB (2022). Modifications to prevent non-target lethality of Goodnature A24 rat traps – effects on rodent kill rates. Management of Biological Invasions 13 (in press).
