Ecological detective work
Top image: Detectives at work. Øystein Varpe and Elke Morgner on the lookout for thieving gulls in Isfjorden. Photo: Eva Therese Jenssen/UNIS.
Longyearbyen is a peaceful place with a close to non-existent crime rate. However, for a short period in spring things change dramatically. The peaceful common eider is being subjected to rather shocking thefts straight in front of its beak! The perpetrator is the gluttonous glaucous gull who does not stop at anything to steal the food out of the eider’s beak. This behaviour is now under scrutiny by UNIS ecological detectives!
22 May 2009
Text: Eva Therese Jenssen
It happens every spring – in April and early May when the snow and sea ice is starting to melt. The birds return to Svalbard bringing with them a definite sign of a warmer season ahead. And the common eiders (Somateria mollissima) make a stop in Longyearbyen to feed on the abundance of shellfish found in Isfjorden and prepare for the coming breeding season.
However, the poor eiders are not left alone to their own devices. In the spring 2008 frequent observations were made in Longyearbyen of glaucous gulls (Larus hyperboreus) stealing the shellfish out of the beaks of eiders after they resurfaced after their meal dive. This is a known, but not investigated phenomenon and UNIS Post Doc Øystein Varpe wanted to find out more of these thefts.
A true Kleptomaniac
The gull species are known for their variety in diet and famous for stealing food when necessary – such as periods where their favourite dishes are not available. Such is the case of the glaucous gull in Svalbard. Both eiders and gulls return to the archipelago in April to fatten themselves up prior to the breeding season.
But, as the eiders have plenty of food to eat in early spring, the glaucous gulls face the opposite situation. It is too early in the season for the kittiwakes and little auks to start breeding, and their eggs and chickens is a major food source for the gulls in summer. With scarce food sources available in April, the gull turns to the eiders that dive to catch mussels, crabs and other benthic prey. The gulls cannot dive, so instead they infiltrate eider groups and simply steal the food out of the eider’s beak!
– We know that the kleptoparasitism the eider is subjected to by the glaucous gull has been observed in Iceland, but we know very little of this particular phenomenon as it has not been subjected to thorough studies, Varpe explains.
Varpe found this so fascinating that he, with funding from the Svalbard Environmental Protection Fund, has started an investigation this spring into this phenomenon. The project’s name is – fitting enough – KLEPTO.
He and biologist Elke Morgner go daily to the harbour areas of Longyearbyen and the shores towards Bjørndalen to observe the birds.
They record flock sizes and feeding activity of the eiders, and count the number of gulls in each eider flock. Some flocks are also filmed for later and more detailed analyses of behaviour.
The detectives started their work in early May and will continue through the month. This year there was sea ice near Longyearbyen all through April, and because the sea ice act as a lid on the eiders’ food, the observation phase was delayed until the eiders could hunt food in open waters.
A “research vessel” with wings…
But why is this scientifically interesting and now the object of a detective campaign?
– First of all, we know very little about the frequency of these thefts and how successful the gulls are in stealing the eiders’ food, Varpe explains. – How important are these theft raids for the gulls? How bad is this for the eiders; as this feeding period is a critical phase for the eiders’ breeding later on? And how do the eiders respond to the gulls’ presence – do they change hunting strategies?
– Second, the eiders can give us some valuable information about the ocean floor fauna around Longyearbyen, based on the sort of shellfish they catch, Varpe says.
When a gull has successfully snatched the meal from the eider, the gull often flies to shore to hack its way into the shell to get to the food. The left-over shells on land give the detectives valuable information about what food the eider hunt for on the ocean floor.
– We can sort of look at the eider as a “research vessel” that can educate us about some aspects of the marine fauna, Varpe says.
This summer the scientist will analyse the films, pictures and logs from the observation period and later on write an article about the phenomenon. Next year, Varpe hopes to extend the project to observe the eider/gull interaction on the outer side of the West Spitsbergen coast, where the eiders feed before the fjord ice has melted.