SATELLITE TELEMETRY
RESULTS
The timing and duration of migratory seasons in North American King Eiders is highly variable among individuals. The least variable migration events are the molt migration and the arrival time at breeding grounds after the spring migration.
Females generally arrive later on molting areas in late summer than males, which is mostly due to the fact that males do not participate in incubation and brood rearing. The main molting area is around the Chukotka Peninsula in the Northern Bering Sea.
Fall migration started anytime between October and late December. Fall migration is generally between 500 - 1500km long and leads the birds from molting areas in the Chukchi or Northern Bering Sea to wintering areas further south. Some birds spent 6 weeks on fall migration, including several stopovers, other birds completed their fall migration within a single week. The last individuals arrived on their wintering grounds in mid January. Most surprising was the fact that almost a third of the birds we tracked did not have a real fall migration at all, but wintered on or near their molting areas.
The birds we tracked wintered in three different regions in the Bering Sea - the Northern Bering Sea around Cape Chukotsky and St Lawrence Island, the Alaska Peninsula and the inner Aleutians, and the coastline of the Kamchatka Peninsula. More than half of the King Eiders used more than one wintering site, and movements ranged from as little as 50 km throught the winter to as far as almost 1500 km in winter alone. Some birds flew back and forth multiple times between wintering sites hundreds of kilometers apart. Despite these extensive movements during the wintering period there were no movements between the three regions described above.
Spring migration started as early as February for some individuals wintering in southern locations, and as late as mid-May for some individuals wintering in Bristol Bay and around the Chukotka Peninsula. Spring migration was generally slower than molt migration and included several stopovers. The most important spring staging area for King Eiders is Ledyard Bay in Northwest Alaska, where all the birds we tracked rested for several weeks during spring migration.
After the final staging period in Ledyard Bay the paths of males and females were very different. King Eiders are believed to pair up during the winter, and while females return to their breeding area year after year, males just follow their female partner to wherever she wants to go. In our study all females returned to the breeding areas in North Alaska where they had been captured in the previous year (Phillips and Powell 2006).
The males however travelled to very distant places, from Taimyr Peninsula in Siberia to the high Canadian Arctic - a range spanning almost half the globe! This shows that King Eiders from arctic regions spanning almost half their global range migrate to the Bering Sea in winter, and highlights the importance of molting, staging, and wintering areas in the Bering Sea.
In 2006 we started to equip juvenile birds with PTTs, and their migration routes and wintering areas were very similar to adult birds. However, juveniles did not return to Arctic waters in summer but remained in the Bering Sea. More juveniles will be tracked in 2007 and 2008.