How volant seabirds benefit from sub-surface predators during multi-predator feeding aggregations.

Multi-predator feeding aggregations are common in marine ecosystems and frequently involve seabirds. Often labelled opportunistic 'scroungers', volant seabirds derive diverse benefits from the association with sub-surface predators (such as cetaceans, pinnipeds, Teleosts) which can significantly enhance their hunting performance. In this opinion piece, we outline the major mechanisms through which sub-surface predators benefit volant seabirds, based on recent quantitative evidence and hypotheses that warrant further research. The mechanisms we identified are: herding prey to the surface, prey detection (local enhancement), reduction of prey cohesion, access to immobilized prey and the attentional overload of prey. Furthermore, we discuss potential interactions between these mechanisms and mechanism-based predictions which can be tested in the field. We propose that the associations with sub-surface predators are ecologically relevant to the extent that they may influence selection breeding sites. We conclude by discussing methodological advancements that have the possibility to further research in this field and go over open questions they might help to answer in the future. This article is part of the theme issue 'Multi-predator feeding aggregations in the pelagic waters'.