Gleaned from the seabird literature

6 05 2013

I always keep my ear to the ground for any seabird science that might be of interest to you, dear Seanetters, and today, I have two items for your perusal!

Manx shearwater in flight near Iceland.

Manx shearwater in flight near Iceland.

The first is a study on the behavior of Manx Shearwaters. These birds nest in underground burrows in colonies mainly in the UK and undertake epic migrations down to the southern Atlantic Ocean during the winter. Breeding surveys can document numbers of chicks hatched, and the genetics of mated pairs, and so on. At sea surveys can determine where shearwaters may be found in large numbers over open water at various times of the year. But to track individual birds throughout their annual life cyle, that was a feat impossible before the advent of high tech, extremely lightweight tracking devices. A team out of the University of Oxford studied Manx Shearwaters using these devices, which can record several years’ worth of data on location, dive depth and duration, and amount of time spent resting on the water’s surface. Their paper in the Journal of the Royal Society Interface  indicates that during the breeding season, the birds must make long commutes out to foraging territories where they will repeatedly dive, surface, and then often take-off for another  flight in what one researcher called a “tortuous” search for food. During their long migrations, the birds stop for focused foraging off the coast of Brazil on the way south, and then in the western Atlantic on their return flight north. The birds also appear to rest more toward the ends of those migrations, an action with which I anthropomorphically sympathize.

The information on the concentrated foraging activities of the Manx Shearwater may also shed some light on the topic of a second paper, this one in Science. The article, entitled Tracking Marine Pollution, focuses on seabirds as top-of-the-food-chain predators particularly vulnerable to concentrating toxic molecules in their tissues. Their extensive foraging trips and migrations mean they may accumulate these chemicals over a huge geographic range. The article focuses both on the ubiquitous marine plastics, as well as the less obvious but more insidious threat they pose: plastics in the water tend to accrue multiple man-made chemicals, sopping them up like little sponges. When seabirds ingest plastics, not only are they at risk from physical damage–obstructions, perforations of the stomach or intestine, simple starvation–but they are also taking in what many researchers term a “poison pill”–a concentrated dose of the pollutants in the water all around them.

Plastics retrieved from the stomach of a Greater Shearwater.

Plastics retrieved from the stomach of a Greater Shearwater.

We often find plastics in the stomachs of Greater Shearwaters here in New England, but our colleagues in the southeast rarely find it in birds washing up on their shores. The interplay between the two articles described above could shed a great deal of light on that phenomenon. Tracking Greater Shearwaters with multi-year data loggers could tell us whether the birds tend to stop and forage in areas with known accumulations of plastic. The fact that the data loggers can tell whether a bird has stopped to forage or just to rest on the surface is an incredible boon to science. We know some seabird colleagues in Canada are working hard on the subject of Greater Shearwater migration, and their work combined with the development of new technologies makes for some exciting times for us, seabird enthusiasts!




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