Call rate and types of calls produced vary with flock movements in wild Pine Siskins (Spinus pinus)

For social animals, communication and social information can help synchronize activities, maintain group cohesion, alert others to predators, and improve individual assessments of food availability. We tested the hypotheses that the call rate and types of calls produced by Pine Siskins (Spinus pinus) may be used to coordinate flock activities. Pine Siskins produce a variety of calls, but call function and use in the wild are unknown. We studied post-breeding flocks of Pine Siskins feeding in discrete patches of native sunflower (Helianthus annuus). We observed and recorded flock vocalizations of Pine Siskins engaged in four behaviors—arrival, baseline (foraging in patch), circling, and departure. Call rate (mean ± SD) was significantly greater during flock movements (arrival 14.60 ± 1.61 calls/min, circling 17.39 ± 5.04 calls/min, and departure 17.10 ± 1.69 calls/min) than during periods of baseline feeding (5.31 ± 0.35 calls/min). Notably, different behaviors were associated with differences in the production of specific types of calls. Additionally, Pine Siskins were more likely to engage in circling behavior and produce more “TBP” (“Zweew” variants) and “R” (“Zree”) calls in the presence of nearby raptor predators. Overall, these results support the hypotheses that Pine Siskins use different types of calls and vary their call rate to help coordinate group movements and predator responses.