Unrecognized importance of hawking prey capture tactics in a tropical plunge-diving seabird

Abstract

Seabirds are critical ecosystem members providing connectivity between marine and terrestrial ecosystems. Seabird foraging is often facilitated by other marine predators (e.g. tuna) that aggregate prey at the surface. Some seabirds have been anecdotally reported to ‘hawk’ (catch mid-air/in-flight) flyingfish and flying squid forced into flight by subsurface predators. Hawking avoids water entry and subsequent take-off, both of which are known to be energy intensive, but its relative importance in foraging has not been quantified. We analysed footage from 25 animal-borne video cameras deployed on red-footed boobies (Sula sula) at Palmyra Atoll to estimate the frequency of hawking, plunge diving and ‘other’ prey capture attempts. Hawking made up 20.3% of all prey capture attempts and had a 39.3% success rate in 2022, but was not observed for the two tracked birds in 2024. An additional 17 individuals were opportunistically observed in the footage making hawking capture attempts, suggesting hawking is a common behaviour, accounting for a greater proportion of foraging effort than previously known. As hawking is only possible when subsurface predators elicit flight escape behaviours of prey, its high frequency suggests such predator facilitation interactions are stronger than currently understood.