Warblers perform less nest defense behavior and alarm calls to human intruders: A result of habituation

Abstract

Human disturbance is caused by the anthropogenic activities in the environment. While human threat to wildlife is considered to be complex (nonlethal recreations and lethal hunting activities). To date, there has been few studies that focus on nest defense behavior of animals to human disturbance. In this study, we tested whether the behavioral response of Oriental reed warblers Acrocephalus orientalis against a human intruder are similar to other nest intruders. We used dummies of common cuckoo Cuculus canorus (the parasite), Eurasian sparrowhawk Accipiter nisus (the predator), Oriental turtle dove Streptopelia orientalis (the neutral control), also a human intruder to induce the nest defense behaviors and alarm calls of Oriental reed warblers. Our results showed that Oriental reed warblers performed less intense nest defense behavior and uttered the least number of calls and shortest duration of calls to a human intruder than those to other nest intruders, suggesting that human pose a low threat level to warblers. Warblers produced different number and duration of alarm calls against the cuckoos, sparrowhawks and doves, even though they performed similar behavioral responses to the three types of avian intruder, indicating that they could distinguish the three types of avian intruders. The present study provided experimental evidence for the different behavioral responses between human disturbance and other types of intruders and suggested that the less intense behavioral response to human disturbance may be the result of habituation.