AUTUMN IMMIGRATION OF REDWINGS TURDUS MUSICUS INTO FAIR ISLE

• Published in: Ibis
• Main Author: Williamson, Kenneth
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1958
• Subjects: Norway; Iceland; Northeast Atlantic
• Online Access: http://dx.doi.org/10.1111/j.1474-919x.1958.tb07962.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1474-919X.1958.tb07962.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1474-919X.1958.tb07962.x

SUMMARY The meteorological conditions governing autumn immigration of the Continental and Iceland races of the Redwing, Turdus m. musicus and T. m. coburni , are compared. The pattern of immigration in a normal year is outlined. Continental Redwings usually appear at Fair Isle with easterly or southeast winds, most abundantly at the end of the first week of October, while small numbers of Iceland birds generally arrive during the same month with cyclonic westerly or northwesterly weather, and form 20–25 per cent of the Redwings trapped. An unusually large invasion of Iceland Redwings in October 1956 seems likely to have been due to special weather factors in the northeast Atlantic rather than to a population peak following exceptional breeding success. The 1956 autumn passage of both races at Fair Isle is summarised. The biggest “broad‐front” invasions by Continental Redwings are associated with anticyclones over Scandinavia when their easterly airflow covers the North Sea, but influxes on a lesser and more localised scale also take place with high pressure over Scandinavia and low‐pressure developments bringing pre‐frontal easterly winds to the North Sea. Direct passage from western Norway to Shetland has been recorded with ridge and col weather over the route, and along the east coast of Britain with cols in the North Sea, but the numbers concerned in the Shetland area are small. The influence of calms, light airs and clear skies (properties of col and anticyclonic weather) on the migration of the Continental race is paramount. Some Iceland Redwings arrive with anticyclonic weather over the northeast Atlantic and a following wind, and “onward passage” of both races from Faeroe‐Shetland is witnessed with col or anticyclonic weather over the “inter‐islands” route. Most movements of coburni , however, have a background of cyclonic westerly or northwesterly weather and are best interpreted as downwind drift. It is argued that if the two races respond alike to weather at the time of departure and during the course ...