Bird and rat carcass persistence in a Hawaiian rainforest managed for rodents using Goodnature A24 self-resetting traps

• Published in: Management of biological invasions 2022-10, Vol.13 (3), p.494-512
• Main Authors: Kreuser, Abigail, Shiels, Aaron, Lepczyk, Christopher, Crampton, Lisa
• Format: Article
• Language: English
• Subjects: Carcasses; Mortality; Palatability; Rainforests; Scavengers; Trapping; Traps; Ungulates
• ISSN: 1989-8649; 1989-8649
• DOI: 10.3391/mbi.2022.13.3.03

Lethal trapping of island invasive rodents is a critical practice used by management organizations to protect native biota. Carcass detection from lethal trapping is dependent on the trapping method, carcass palatability, and scavengers present. Goodnature A24 self-resetting rat traps are an effective tool in remote areas and complex terrain because traps can be visited at 4–6 month intervals and produce multiple carcasses during that interval. The goal of this study was to determine whether we are a) underestimating target mortality with carcass counts and b) failing to detect non-target mortality between A24 trap checks at two field sites on the island of Kauai. Both sites have established Goodnature A24 trap grids with 300 A24s deployed by the Kauai Forest Bird Recovery Project (KFBRP), and one site is fenced to exclude invasive ungulates. KFBRP conducts routine trap checks every four months, finding 0–3 rat or mouse carcasses at each trap. We assumed that traps kill more animals than indicated by carcass counts because 75% of traps have counters to record when traps fire, and counter tallies usually exceed carcass counts. In 2018 and 2019, several bird carcasses were found under traps; therefore, we needed to investigate the likelihood that non-target mortality went undetected. In May 2019, we placed 60 carcasses (30 non-native birds and 30 rats) at a fenced site, and 60 carcasses (30 bird, 30 rat) at an unfenced site, in both gulches and uplands. Carcasses were periodically surveyed for 120 days after deployment. The unfenced site had greater removal rates, notably in gulches; 33 of 60 carcasses remained detectable, compared to 52 of 60 carcasses at the fenced site. Bird and rat carcasses did not differ in persistence, and taxon did not affect scavenger preference. These results suggest that significant non-target mortality has not gone undetected in our A24 trap grid because we are likely to detect most target and non-target carcasses after four months in fenced areas, and especially upland unfenced areas. However, we are less likely to detect carcasses in the unfenced gulches where ungulate scavengers are prevalent, and increased monitoring may be needed in such gulches.