24 June 2009

The long subantarctic commute


Although New Zealand has a huge selection of seabirds, and is the centre of diversity for many groups, we are still in a very early stage in understanding the behaviour and ecology of these species (see the recent ecoLincNZ blog post by Jessica Parisi). Mostly this is understandable. Seabirds usually live on remote oceanic islands that are difficult to get to and even more difficult to stay on for any length of time. More importantly seabirds spend most of their time at, well, sea. What they get up to hundreds of kilometers from land is difficult to study. Luckily, technology is providing solutions. Tina Troup, as part of a Master of Science, was interested in the foraging of royal albatoss (Diomedea epomophora) during their breeding season. Where did the go? What did they do? Using satellite transmitters to track position, dry-wet recorders to identify when birds were on the water and heart-rate monitors to examine how much work the birds were doing, Tina trooped off to Campbell Island in the New Zealand sub-Antarctic zone.

More...

Ten southern royal albatross were tracked through incubation (January/February). In a recent paper published in New Zealand Natural Sciences (34: 19-28) Tina, along with Adrian Paterson and Craig Sixtus from Lincoln University, report on their findings. Royal albatross appear to have specific foraging grounds that are hundreds to thousands of kilometers from Campbell Island. This causes them fly in what we term a 'commute, forage, commute' foraging strategy. The birds would generally commute in a direct movement, covering up to 800km/day. Foraging was more haphazard and the birds covered less than 180km/day, making frequent changes in direction and landing often. Once birds were satisfied with an area they would then commute to the next area to forage.

Wind direction and strength were shown to be important in determining how quickly the albatrosses could move and in the directions that they tended to move in. Winds from head, tail and right angles made it difficult to return to the colony. Likewise, bird mass was also important with lighter birds under 9kg finding it difficult to land in winds over 40km/hr. Overall, there appeared to reasonable flexibility in starting each foraging trip with birds able to select different foraging sites depending on the direction and intensity of the winds around Campbell Island. Obviously, only being able to follow ten birds for a month limits what we can discover about the biology of the royal albatross. However, a small window has opened onto a part of their lives that we know little about.

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