Discrimination of acoustically similar conspecific and heterospecific vocalizations by black-capped chickadees (Poecile atricapillus)

Can you hear me now? The effect of signal degradation on perceived predator threat in black-capped chickadees (Poecile atricapillus)

Avian predators vary in their degree-of-threat to chickadees; for example, smaller owls and hawks are of higher threat to chickadees as they can easily maneuver through the trees, while larger predators cannot. We conducted an operant go/no-go discrimination task to investigate the effect of signal degradation on perceived threat. Chickadees were trained to respond to high-threat northern saw-whet owl (NSWO) or low-threat great horned owl (GHOW) calls that were recorded at short distances, and then tested with high- and low-threat owl calls that were rebroadcast and re-recorded across six distances (25 m, 50 m, 75 m, 100 m, 150 m, and 200 m). Subjects were further tested with high-threat and low-threat synthetic tones produced to mimic the natural calls across the six distances. We predicted that birds would perceive and respond to: (1) high-threat predator calls at longer distances compared to low-threat predator calls, and (2) synthetic tones similarly compared to the stimuli that they were designed to mimic. We believed chickadees would continue to perceive and respond to predators that pose a high threat at further distances; however, only responding to low-threat stimuli was consistent across distance recordings. Synthetic tones were treated similarly to natural stimuli but at lower response levels. Thus, the results of this study provide insights into how chickadees perceive threat.

The effects of anthropogenic noise on feeding behaviour in black-capped chickadees (Poecile atricapillus)

Anthropogenic noise has been shown to impact animal behaviour. Most studies investigating anthropogenic noise, and the detrimental effect it has on behaviour, have been conducted in the field, where a myriad of covariates can make interpretation challenging. In this experiment, we studied the effects of an approximation of anthropogenic noise, simulated with brown noise, on the feeding behaviour of wild-caught black-capped chickadees in a laboratory setting. We measured the amount of time spent eating while subjects heard either conspecific calls, brown noise, or a combination of calls and brown noise. We found that subjects fed more in the silence following playback than during the playback itself for all types of stimuli, suggesting that chickadees may shift their feeding behaviour to avoid feeding during periods of noise. The ability to adapt to changing environments (e.g., varying noise levels) may allow species to thrive in the presence of anthropogenic noise. Our findings outline a laboratory-based method that could be adopted and adapted to examine a variety avian species and of types anthropogenic noise.