Survival rates differ among little auks Alle alle from different colonies despite shared wintering grounds

Geolocators revealed that little auks breeding at Spitsbergen, Bear Island and Franz Josef Land to some extent share wintering grounds. Despite using the same area, annual survival rates did not necessary synchronize between colonies.

Combining tracking and capture-recapture data

Sharing the same environment during winter may synchronize fluctuations of distant populations. This effect corresponds to the synchronization in the dynamics of populations by density-independent factors (like climate) that are correlated across wide regions and which may increase the risk of extinction. Here, by combining multi-colony tracking with long-term capture-recapture data, we studied the winter distribution and annual survival of the commonest Arctic seabird, the little auk. We assessed whether little auks from different breeding populations in Svalbard and on Franz Josef Land used the same wintering grounds and if this led to synchronized survival rates.

No synchrony in adult survival

Our results indicated that birds from three Svalbard colonies generally spent the winter in the same area, in the Labrador Sea eastwards to the Iceland Sea, although there were differences in the proportions of birds from each colony that used the different areas. Most birds from Franz Josef Land spent the winter in the Barents Sea, but some individuals wintered in the Iceland Sea together with Svalbard populations. Survival data from the three Svalbard colonies collected in 2005-2018 indicated that sharing wintering grounds did not result in a synchronization of annual survival rates. Although survival is thus also affected by factors outside the wintering area, the study did highlight the Iceland Sea as an important wintering area for little auks, such that environmental changes in this area could have widespread impacts on many populations.

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• Sharing wintering grounds does not synchronize annual survival in a high Arctic seabird, the little auk