INLAND FALL MIGRATION OF RED-THROATED LOONS

Abstract

Lake Ontario is the only Great Lake where a significant number of Red-throated Loons are seen during fall migration. Observations from Hamlin Beach State Park, New York during fall months, 1993–1997, were used to analyze their movements. Annually, an average of 7750 Red-throated Loons were counted moving mostly west on the south shore of Lake Ontario. Their median date of occurrence was 22 November with the peak period of migration from 17 November to 1 December. The earliest migrants appeared in mid-October and became extremely rare after December. The seasonal timing on Lake Ontario corresponds to that observed on the Atlantic Ocean at Avalon, New Jersey. Their occurrence on Lake Ontario was analyzed with respect to local and mid-arctic weather conditions. The variable which best correlates with their appearance is mid-arctic temperature. On average, large flights (>200 loons per day) began on Lake Ontario 3 d after the invasion of a cold air mass is centered approximately 1100 km to the north. After this event, the period of sustained flight was maintained for 7–16 d when 80% of migration takes place. The fall arrival pattern of Red-throated Loons on Lake Ontario implies that migration takes place under any type of weather conditions, but local temperature, wind direction, and the movement of cold fronts are all weakly correlated to their migration. Inland fall sight records of Red-throated Loons from American Birds suggest that the main inland migration route is through western Pennsylvania. This is consistent with observations of Red-throated Loons leaving the western end of Lake Ontario. A smaller part of the inland migration is east of Lake Ontario based on these records.