Migrating geese and their food plants
Top image: Svalbard has many important stops for migrating geese during the spring. Here is barnacle geese (foreground) and light-bellied brent geese grazing in Vårsolbukta during spring. Photo: Christiane Hübner/UNIS.
Svalbard has many important stopover sites for migrating geese during the spring. But only a few of these stopover sites are known today. There is a pressing need to identify more of these sites in order to implement effective management actions, concludes Christiane E. Hübner in her PhD thesis, which she will defend at UNIS March 8th 2007.
2 March 2007
Press release from the University Centre in Svalbard and the University in Tromsø
Hübners thesis from the University in Tromsø and the University Center in Svalbard (UNIS) gives new insight into the life of migrating geese in the Arctic areas and how Svalbard plays an important role in the northern bound spring migration towards the breeding areas.
Hübner has examined the feeding pattern of geese in Vårsolbukta at Van Mijenfjord in Svalbard during three spring seasons. This area is used by all three geese species breeding in Svalbard. The barnacle goose Branta leucopsis was most numerous with numbers up to tenfold of those of pink-footed geese Anser brachyrhynchus and light-bellied brent geese Branta bernicla hrota.
Individual barnacle geese spent only a few days in the Vårsolbukta, although the time between their departure from the Norwegian mainland until arrival at the Arctic breeding grounds suggests that they spend up to several weeks in pre-breeding stopover sites.
This indicates that the geese use more than one stopover site to feed before they arrive at the breeding grounds. By using several stopover sites along their migratory route, the geese can adjust their timing and body reserve balance continuously according to what weather and snow conditions they encounter during the trek. Moreover, pre-breeding stopover sites may function as a buffer area, where body reserves can be replenished after arrival in the Arctic.
The importance of moss
Moss is the most important food plant for geese during early arctic spring and the intensive consumption may have a large impact on the vegetation. Clipping experiments showed that intensive grazing has a potential to reduce subsequent productivity of the moss shoots.
However, natural grazing had little effect on the following moss growth compared to ungrazed moss. Hübner concluded that biomass removal in moss is compensated for by growth facilitation due to other aspects of goose grazing, such as mechanical breaking-up of the dense moss mat.
Grass availability during pre-breeding is low, but geese generally prefer grass tillers over moss. The fresh grass leaves are small and hidden in the vegetation and thus, selection of grass tillers is primarily driven by their conspicuousness. Moss is a low quality food plant compared to grass and the high consumption of moss by geese early in spring results mainly from the low availability of the preferred grass.
Vårsolbukta is an important stopover site for geese and is used both as a stepping stone in a chain of stopover sites (birds from distant breeding colonies) and as waiting area to fine-tune the arrival at the nesting sites without sacrificing body reserves (birds from colonies close-by). These observations at Vårsolbukta indicate that stopover sites in Svalbard have multiple functions and they emphasize the need to identify more of these important sites for spring migrating geese in order to implement effective management actions.
About the candidate:
Christiane E. Hübner (35) is from Heidelberg in Germany. She is Diplom-Biologin from the University in Tübingen and the University in Tromsø in 1999.
The PhD is financed by the Norwegian Research Council; the Roald Amundsen Center for Arctic Research and the Norwegian Polar Institute.
The defense will be at UNIS on 8 March 2007. Hübner is currently working as a coordinator at Svalbard Science Forum.