Immature Long-tailed Skuas Stercorarius longicaudus in Swedish Lapland in 2009

Rob Van Bemmelen

doi:10.34080/os.v20.22634

Abstract

Between 12 and 27 June 2009, 10 immature Long-tailed Skuas Stercorarius longicaudus were recorded in breeding areas in Swedish Lapland. Based on plumage characters, these were aged as 3rd calendar year birds. The fraction of immatures in the total number of aged birds was 4–10%, which seems to be in accordance with maximum abundances of immatures reported in earlier studies. The first immature birds were sighted about two weeks after the arrival of adults. There was no breeding this year, and adults and immatures both departed at the end of June. Prospecting before being recruited into the breeding population may enhance early arrival in later years, which in turn may increase the probability to recruit.

Highlights

In long-lived, long-distance migrants, immatures may visit future breeding grounds in one or more years before breeding for the first time
The slightly barred axillaries and the blotched upper breast indicate its immaturity. These sightings confirm the occurrence of 3rd cy Long-tailed Skua at the Swedish breeding grounds
Plumage characteristics of immatures recorded in 2009 in Ammarnäs are consistent with what has been described for 3rd cy Long-tailed Skua (Howell 2007)

Summary

Introduction

In long-lived, long-distance migrants, immatures may visit future breeding grounds in one or more years before breeding for the first time These prospecting visits and breeding commence at a higher age in larger species and species with a higher expected life-span (Becker & Bradley 2007, Weimerskirch 2002). For the Long-tailed Skua Stercorarius longicaudus, a transequatorial migrant seabird breeding on (inland) Arctic tundras, it has been suggested that breeding commences in the 4th cy (de Korte 1985). Immatures in their 2nd and 3rd cy have been recorded prospecting the breeding grounds. I report observations of 3rd cy Long-tailed Skuas in Swedish Lapland in 2009

Methods

Results

Conclusion