Graded‐risk sensitivity in northern European mixed‐species flocks of tit and nuthatch species

• Published in: Ethology 2022-05, Vol.128 (5), p.437-442
• Main Authors: Benson, Scott A., Kelly, Jeffrey R., Kullberg, Cecilia, Krama, Tatjana, Vrublevska, Jolanta, Krams, Indriķis, Freeberg, Todd M.
• Format: Article
• Language: English
• Subjects: anti-predator behavior; calling; Calling behavior; Cost benefit analysis; Head movement; Lophophanes cristatus; Orientation effects; Parus major; Poecile montanus; Predation; predator-risk-sensitive foraging; Predators; Risk taking; Seeds; Sensitivity; Sitta europaea; Species; Vigilance
• ISSN: 0179-1613; 1439-0310; 1439-0310
• DOI: 10.1111/eth.13276

Avian species often use anti‐predator calls such that the costs and benefits of vigilance are distributed within the group. Some species respond differentially to graded risk by attending to relevant predator cues, such as head orientation and gaze direction. One benefit of graded‐risk sensitivity is fewer missed foraging opportunities. It is not known how the makeup of risk response behaviors in mixed‐species flocks may relate to the relative nuclearity of each species in the flock. In the current study, predator models were presented to two nuclear and two satellite species of passerines that frequently occur in natural mixed flocks. Predator models either faced toward or away from a nearby stocked feeder to simulate high and low risk of predation, and calling and seed‐taking rates of the present flock were recorded. The nuclear species, great tits (Parus major) and crested tits (Lophophanes cristatus), took more seeds when the predator faced away from the feeder than toward it. The satellite species, Eurasian nuthatches (Sitta europaea) and willow tits (Poecile montanus), did not show an effect of predator orientation. No species showed consistent differences in calling behavior relative to predator orientation, although insufficient calling data for great tits prevented analysis for this species. The results of this study suggest that one aspect of nuclearity in mixed‐species flocks is a tendency for graded‐risk sensitivity, or alternatively, that satellite species are more sensitive to mere predator presence rather than to predator orientation cues. Graded‐risk sensitivity was tested in four species (crested tit, great tit, willow tit, and Eurasian nuthatch). All four species limited their calling and feeding behaviors near a predator model, but crested tits discriminated between predators facing toward or away from them for both feeding and calling behaviors, and great tits did so for feeding behaviors. We believe the species difference may reflect roles within mixed‐species flocks, as the two nuclear species were more discriminating than the two satellite species.