Predator-risk-sensitive foraging behavior of Carolina chickadees (Poecile carolinensis) and tufted titmice (Baeolophus bicolor) in response to the head orientation of snake predator models

Nest box entrance hole size can influence nest site selection and nest defence behaviour in Japanese tits

Birds have the ability to assess the risk of predation in their environment and adjust their antipredation strategies based on this risk information. However, whether nest site selection has effect on subsequent nest defence behaviour has not been studied. In this study, we aimed to determine whether the Japanese tit (Parus minor) exhibits a nest-box hole size preference and whether the entrance hole sizes of nest boxes influence the nest defence behaviour of tits. We hung nest boxes with three different entrance hole sizes (diameters: 6.5 cm, 4.5 cm and 2.8 cm) in our study sites and investigated which nest boxes were occupied by tits. In addition, by using dummy-presentation experiments, we observed the nest defence behaviours of tits that nested in boxes with 2.8 cm and 4.5 cm entrance holes towards common chipmunks (Tamias sibiricus, a small nest predator able to enter these holes) and Eurasian red squirrels (Sciurus vulgaris, a large nest predator unable to enter the 2.8 cm entrance hole). The tits that bred in nest boxes with 2.8 cm entrance holes exhibited more intense nest defence responses to chipmunks than to squirrels. In contrast, the tits that bred in nest boxes with 4.5 cm entrance holes exhibited similar nest defence responses to chipmunks and squirrels. Additionally, Japanese tits that bred in nest boxes with 2.8 cm entrance holes exhibited more intense behavioural responses to chipmunks than those that bred in nest boxes with 4.5 cm entrance holes. Our results suggested that Japanese tits prefer to occupy nest boxes with small holes for breeding and that nest-box characteristics influenced their nest defence behaviour.

Do Carolina chickadees (Poecile carolinensis) and tufted titmice (Baeolophus bicolor) use predator eyes in risk assessment?

Previous studies have found that Carolina chickadees and tufted titmice use a predator's head orientation to determine risk, taking fewer seeds from a feeder if an avian predator model's head is facing the feeder while ignoring the head orientation. In addition to head orientation, eyes are a cue of predator risk. In the current study, I examined whether or not chickadees and titmice used the presence of eyes of a predator model to determine when to forage for food. Plastic owl models, with their eyes covered or uncovered, were presented to wild flocks of chickadees and titmice. To test whether or not chickadees and titmice would respond to the presence of eyes, the number of seeds taken and the calling behavior of birds were compared between the two types of predator presentations (eyes covered or uncovered). Chickadees and titmice took fewer seeds when the eyes were uncovered than when they were covered. Chickadees also gave significantly more introductory notes, often used in association with the presence of predators or risk, in their calls when the eyes were visible than when the eyes of the predator model were covered. The results indicate that chickadees and titmice can use the presence of eyes on predators to determine predation risk and possibly use eye gaze to determine where a predator is looking.

Selective reactions to different killer whale call categories in two delphinid species

The risk of predation is often invoked as an important factor influencing the evolution of social organization in cetaceans, but little direct information is available about how these aquatic mammals respond to predators or other perceived threats. We used controlled playback experiments to examine the behavioral responses of short-finned pilot whales (Globicephala macrorhynchus) off Cape Hatteras, NC, USA, and Risso's dolphins (Grampus griseus) off the coast of Southern California, USA, to the calls of a potential predator, mammal-eating killer whales. We transmitted calls of mammal-eating killer whales, conspecifics and baleen whales to 10 pilot whales and four Risso's dolphins equipped with multi-sensor archival acoustic recording tags (DTAGs). Only playbacks of killer whale calls resulted in significant changes in tagged animal heading. The strong responses observed in both species occurred only following exposure to a subset of killer whale calls, all of which contained multiple non-linear properties. This finding suggests that these structural features of killer whale calls convey information about predatory risk to pilot whales and Risso's dolphins. The observed responses differed between the two species; pilot whales approached the sound source while Risso's dolphins fled following playbacks. These divergent responses likely reflect differences in anti-predator response mediated by the social structure of the two species.