The little auk is one of the most numerous seabirds in the world, and it is estimated that an adult individual requires up to 60 000 copepods per day. To achieve such a performance, it has been suggested that the little auk might capture their prey by filter-feeding. However, a new study shows that the little auk rather uses a suction technique, a behaviour never before seen in seabirds.

The video, which is played in slow motion, shows how two little auks dive and capture zooplankton in an artificial pool.
Video: Manfred R. Enstipp

There are many different foraging strategies in the marine ecosystem, and trophic flow and food web construction are conditioned by these different strategies. The largest of all in the marine system, whales, evolved an efficient foraging technique that maximizes plankton intake – filter feeding. Seabirds are mainly piscivorous or planktivorous and they use raptorial feeding, seizing prey items individually, a strategy that compared to filter feeding is not very efficient. Plankton-feeding seabirds, such as the little auk Alle alle, have an extremely high daily intake of copepods (approx. 60 000), and it is assumed that they are raptorial feeders, which means that they have to catch 6 copepods per second underwater to achieve that requirement. The researches in this study wanted to look closer into the feeding technique of little auks, and their hypothesis was that the little auk have the ability to filter feed. They captured little auks from a colony close to Ny-Ålesund, Svalbard, and placed them in a pool with a calculated biomass of zooplankton to observe their feeding technique. Several cameras in the pool were used to document the little auks’ feeding technique.

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In this study, the researchers found no evidence of filter feeding, but they did find evidence of suction feeding. The video shows how the little auk visually locates its prey (zooplankton), then opens its beak and likely creates a suction flow which drags the prey into its mouth. This feeding technique is common in fish and marine mammals, but has never been observed in a seabird. It is a more efficient technique than raptorial feeding, and may allow little auks to better cope with changes in the composition of prey species.

Contact person: Sébastien Descamps, Norwegian Polar Institute