As water along dirt roads in the Pantanal floodplains diminishes, aquatic fauna becomes restricted to shallow pools. At the end of the 2009 dry season, we filmed giant otters living in pools predating on yacare caimans. Such predation has not been recorded in giant otters inhabiting the Pantanal. Individual otters captured sub-adult caimans. The otters did not share the prey, but conspecifics stole it after conflicts. Caiman predation could be related to resource scarcity in these marginal environments. Information on diet and interactions of endangered populations may underestimate their trophic niche when they recover from over-hunting and expand into sub-optimal habitat.

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