Southeastward shorebird migration over Nova Scotia and New Brunswick in autumn: a radar study

Abstract

Shorebirds departed over the Atlantic intermittently by night and (in lesser numbers) day in late summer and early autumn. Migrations were broad-front and usually began inland (including Bay of Fundy), often 1–2 h before sunset. Tracks were straight, with daily means of 110–170° (overall mean 134°). About 69% were flying on tracks directed too far east to reach South America without a course change; the roles of wind drift and heading adjustments in effecting this course change are uncertain. Ground speeds were 74 ± SD 17 km/h; altitudes were often high (mean 2.0 km, 5% of flocks above 4.4 km, highest 6.65 km). Many departed with W–NW winds and fair weather behind cold fronts or E or N of high pressure areas, but some took off ahead of or caught up with and penetrated cold fronts. Mean tracks were correlated with wind direction, but were rarely downwind. Their deviation from downwind was unrelated to visibility, cloud, or magnetic disturbance (K index). Dispersion of tracks did not change consistently during nights or days and was unrelated to wind or K index. Dispersion at night was slightly greater in inclement than fair weather.