Presence of mammalian predators decreases tolerance to human disturbance in a breeding shorebird

Nonlethal disturbance can impose fitness costs, particularly during sensitive life history stages such as reproduction. Prey animals are thus expected to assess the costs and benefits of expressing antipredator behavior in different circumstances and to respond optimally according to the perceived risk of predation. One prediction of this hypothesis is that the response to nonlethal disturbance should be elevated when the risk of predation is high, although few studies have tested this prediction with respect to the distribution of actual predators in nature. We used landscape-level variation in the distribution of large mammalian predators (feral cats) to investigate antipredator behavior in a small breeding shorebird, the Two-banded Plover Charadrius falklandicus. We used 8 sites in the Falkland Islands and Argentina and measured the flushing distances of incubating Two-banded Plovers in response to a controlled human approach to the nest. We found that flushing distances were increased at sites where mammalian predators were present and decreased where exposure to humans was high. These effects were additive, and we interpret them as the effects of generalization and habituation, respectively.