Article

Albatrosses are thermal ecosystem engineers that keep caterpillars warm

Steven Chown

Wandering Albatross, Diomedea exulans, on Marion Island. Photo by Brent Sinclair

One of the most noticeable features of the coastal plains of the sub-Antarctic Prince Edward Islands is the numerous wandering albatrosses dotted about the landscape on their large nests. This species, IUCN red-listed as vulnerable, usually attracts attention because of the grace of its flying adults, the plucky chicks which crown their nests all winter enduring rain and snow, and its plight at the hands of illegal, unregulated and unreported long-line fishing.

However, a researcher from the DST-NRF Centre of Excellence for Invasion Biology (CIB) and one of his postdoctoral associates of the Department of Botany and Zoology at Stellenbosch University have shown that the albatrosses are remarkable for another reason - they act as giant hot water bottles for caterpillars who survive in the extreme temperatures.

Dr Brent Sinclair and Prof Steven Chown have demonstrated that, by sitting on their nests, the birds act as heat islands for a keystone caterpillar species, and in so doing elevate growth caterpillar rates and reduce the ill-effects of cold (published online in Biology Letters).

"It's simply amazing", remarked Sinclair. "These birds elevate nest temperature more than 5°C above ambient and bring caterpillars up to their optimum feeding temperature".

These temperatures also reduce cold injury as Sinclair and Chown have demonstrated in another work recently published in the Journal of Experimental Biology.

The caterpillar of the flightless moth Pringleophaga marioni. Photo by Brent Sinclair

"Researchers have long known that the best place to find caterpillars is in recently abandoned albatross nests," said Chown. "Now we know why."

"It's not nutrients that they are after, as has long been thought, but rather they benefit from elevated temperatures."

At Marion Island, the caterpillars (which belong to a tineid, flightless moth, Pringleophaga marioni) are essential for nutrient recycling because they are detritivores that process large quantities of litter. Owing to the absence of herbivores, most plant material enters the detritus web.

It now seems that threats to albatrosses may not only be bad for the species, but also for ecosystem functioning on the islands because of their role as thermal ecosystem engineers for the caterpillars. The caterpillars are also under pressure from introduced house mice.

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