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ENGINEERING BY ALBATROSSES?

Tanya Haupt & Rina Groenewald report from Marion Island

Most people are fascinated by Wandering Albatrosses. They are huge, gorgeous birds, which always manage to turn heads. But few who marvel at the birds pause to think about their nests. Ecological entomologists on Marion Island are the exception. And we have just joined that group, although our expertise ranges from molecular genetics to marine ecology.

Tanya shows that this is nest number 3 for today! Despite the freezing cold, we were eager to dig into yet another recently abandoned Albatross nest.

It has long been known by Marion Islandís entomological visitors that the best place to look for caterpillars of the indigenous flightless moth, Pringleophaga marioni, is the recently abandoned nests of Wandering Albatrosses. They are much more abundant in nests than they are elsewhere. The French know this too, and based on work at the Crozet Islands they suggested that what the caterpillars are after is elevated nutrients. After all, better nutrients likely mean better growth for this detritus-feeding species. On Marion the nutrient idea does not seem to hold up. Nutrients are the same in nests as they are elsewhere or perhaps even lower than these other areas. Rather, a recent study has suggested that the caterpillars achieve such high numbers in nests by virtue of the fact that the nests are kept warm by incubating albatrosses and later by the growing chick. Indeed, nests are typically 5°C warmer than the surrounding environment, and this lasts for nearly a year, from egg laying to fledging of the chick. These elevated temperatures mean lower probability of cold injury, which lowers caterpillar growth rates, and more optimal conditions for growth. So, thatís how the albatrosses are thermal ecosystem engineers Ė they thermally engineer a more hospitable environment for the caterpillars.

Well, thatís the story Ė so far! Our degree work is based on determining whether this is, in fact, the case. To do so we will take a wide variety of approaches and will be collaborating with scientists from Canada (Dr. Brent Sinclair) and from Australia (Dr. Justine Shaw), and will be working in the research labs of Profs Steven Chown and Bettine Jansen van Vuuren. In particular, we will be determining the preferences of caterpillars for nest material vs. other vegetation, the optimum temperatures for movement, the densities of caterpillars inside and outside nest, and the relatedness of caterpillars. In the latter case we also have collections from neighbouring Prince Edward Island that were made in December by Justine and Steven. So, we can also resolve the question of whether one or two species are found at the Prince Edward Islands. Earlier studies suggested that Pringleophaga marioni is found on Marion and Prince Edward, but that another species, P. kerguelensis, is also found on Prince Edward. We shall see!

So now we find ourselves on Marion Island. And what a place! The wanderers are head turners, thereís no doubting that. And the nests really do have more caterpillars than elsewhere, but that does not make looking for them any warmer. Our work means we go out in freezing rain, high winds, and whatever else the weather has in store for us. Good gear helps, but the warm lab at the end of the sampling session remains a great attraction. Our experiences here will not easily be forgotten. The visit to the islands was nothing like we imagined it would be and therefore so much more memorable.