Rodenticide baiting black rats (Rattus rattus) in mangrove habitats

Context. Mangroves and intertidal habitats have been identified as particularly challenging environments for bait application within both tropical and temperate environments, because bait applied to areas that are tidally inundated could degrade rapidly or become inaccessible to rats. Aims. To determine rat density, ranging behaviour and probability of detection using different monitoring devices; additionally, to determine the availability (persistence, durability and uptake) of rodenticide baits within tidally inundated mangrove habitats. Methods. The population biology of black rats (Rattus rattus) was studied in two contrasting mangrove habitats on Europa Island, and spatially explicit mark-recapture studies were performed to estimate densities and activity of rats. A series of bait availability trials was conducted to determine the durability of rodenticide baits on the ground and uptake in the canopy ('bait bolas'). Key results. Black rats were found to be abundant in mangrove, and despite daily tidal inundation, still maintained ranging behaviour consistent with rats in adjacent terrestrial habitats. Larger rodenticide bait blocks remained within tidally inundated habitat throughout tidal cycles and were available and remained palatable to rats for at least three consecutive nights, although strong bait competition occurred with crabs. Bait bolas were available in mangrove canopy exclusively to rats and consumption commenced on the first night. Conclusions. The results provide evidence that mangrove habitats are an important habitat for rats, but the biology of rats in these habitats does not meaningfully differ from adjacent terrestrial habitats. With the use of larger rodenticide blocks, tidal inundation does not affect bait availability, but crabs remain a major competitor for these baits. Alternatively, the present study revealed that bait bolas limit bait access to rats alone. Development as an aerial eradication technology should be also recommended. Implications. These results provide a proof of concept that eradication of rats from tidally inundated habitats such as mangrove should be possible with only small modifications to current best practice.