The enduring toxicity of road-killed cane toads (Rhinella marina)

The primary ecological impact of invasive cane toads (Rhinella marina) in Australia is mediated by their powerful toxins, which are fatal to many native species. Toads use roads as invasion corridors and feeding sites, resulting in frequent road-kills. The flattened, desiccated toad carcasses remain highly toxic despite being heated daily to >40°C for many months during the tropical dry-season. In controlled laboratory experiments, native tadpoles (Cyclorana australis, Litoria rothii), fishes (Mogurnda mogurnda) and leeches (Family Erpobdellidae) died rapidly when we added fragments of sun-dried toad to their water, even if the native animals had no physical access to the carcass. Given the opportunity, native tadpoles and fishes strongly avoided the vicinity of dried toad fragments. Hence, long-dead toads may contaminate roadside ponds formed by early wet-season rains and induce avoidance and/or mortality of native anuran larvae, fishes and invertebrates. Our studies show that the toxicity of this invasive species does not end with the toad's death, and that methods for disposing of toad carcasses (e.g., after culling operations) need to recognize the persistent danger posed by those carcasses.