Many species of tropical seabirds rely on subsurface predators such as tuna and dolphins to drive prey close to the ocean's surface. We observed seabird foraging events from fishing vessels around the island of Oahu, Hawaii, to determine the prevalence and relative importance of different subsurface predators to seabird foraging. Sixty-nine seabird foraging events were observed, in 62 of which the presence and/or identity of subsurface predators could be determined. Of those 62, all but two involved subsurface predators and accounted for 99.8% of all foraging birds. Skipjack tuna Katsuwonus pelamis were the predominant (81%) subsurface predator involved in seabird feeding events, with odontocetes Stenella attenuata and Pseudorca crassidens (8%), mahimahi Coryphaena hippurus (6%), and yellowfin tuna Thunnus albacares (2%) being less common. Wedgetailed shearwaters Puffinus pacificus and brown noddies Anous stolidus foraged in association with tuna schools more often than would be expected by chance alone. Red-footed boobies Sula sula, in contrast, did not associate with any subsurface predator in greater proportion than what would be expected by chance. Nine additional seabird species were observed foraging in association with subsurface predators, but not in numbers large enough for statistical analysis. This study highlights the value of regional investigations able to uncover the variable nature of seabird -subsurface-predator associations. The finding that, in Hawaii, at least 2 species of seabirds showed tight dependence on tuna underlines the need for tuna fishery management to address the potential indirect ecological effects of fishing.

Invasive ants are a significant conservation concern and can have far-reaching effects in ecosystems they invade. We used the experimental control of ant numbers on two pairs of small (\5 ha) offshore islets dominated by either the big-headed ant, Pheidole megacephala or the tropical fire ant, Solenopsis geminata to investigate the influence of these species on seabird hatching success, fledging success and weight. Limited unpublished observations of both ant species attacking nesting seabirds exist, but the frequency of attacks or how they affect seabird growth and survival are unknown. Islandwide treatments with hydramethylnon resulted in the eradication of P. megacephala and the temporary reduction of S. geminata densities. No difference in hatching success, growth, or fledging success of Wedge-tailed Shearwaters (Puffinus pacificus), a common colonial nesting seabird in the Hawaiian Islands was observed on the pair of islets dominated by P. megacephala. On islets dominated by S. geminata, ant control resulted in a temporary increase in fledging success. Injury frequency increased dramatically on the untreated islet (8.3-100%) while remaining the same on the treated islet (27-38%). Severely injured chicks (i.e., chicks that lost [20% of tissue on their feet) weighed significantly less than uninjured chicks and did not fledge. It is unclear if the chicks were being preyed upon or stung in defense of nearby ant colonies. Radical changes in invasive ant populations have been noted, and booming ant populations could cause short-term, but widespread damage to seabird colonies. The negative effects of invasive ants on seabirds may be difficult to detect, and therefore unknown or underestimated throughout the world where the two groups overlap.

No abstract