In the Danger Zone: Wrens Respond More Strongly to Experimentally Simulated Predators Near Their Nest

ABSTRACT Animals routinely face predation risk, and the behaviors that animals exhibit in the face of danger have life and death fitness consequences. When encountering predators, animals may exhibit divergent responses depending on perceived risk to themselves and their offspring. We used a predator presentation experiment to study the vocal responses of breeding rufous‐and‐white wrens ( Thryophilus rufalbus ) to simulated ferruginous pygmy‐owls ( Glaucidium brasilianum ) at different distances from their active nests. We hypothesized that wrens' responses would vary with perceived predation risk, and we predicted that closer distances between the predator and wrens' nests would elicit stronger responses. We used lifelike 3D‐printed models and acoustic playback to simulate owls at two distances from the nests (5 and 20 m) simulating high and low predation risk, respectively, as well as a non‐predatory songbird as a control stimulus. We found that rufous‐and‐white wrens were highly vocal in response to predator simulations, producing both songs and alarm calls, and exhibiting substantial variation in intensity of response. Males vocalized more quickly in response to predators near the nest than to predators far from the nest, whereas females showed similar latencies of response. Wrens approached near‐nest predators more closely than far‐from‐nest predators. Together, males and females showed stronger calling responses to near‐nest predators compared to far‐from‐nest predators. Song rate did not change in response to model presentations for both sexes, but males performed more songs than females across all treatments. Our results reveal that birds respond more strongly, and with higher calling rates, in the face of heightened predation risk. Therefore, breeding birds exhibit divergent responses in different scenarios, displaying higher intensity vocal responses to predators nearer to their nests.