Sex-specific variation in breeding-ground departure decisions and detection rates during southbound migration in West Atlantic Flyway Whimbrels (Numenius phaeopus).

Understanding movement ecology of long-distance migrants is essential for effective conservation. We showed that West Atlantic Flyway Whimbrels (Numenius phaeopus) depart their breeding grounds at different times based on breeding latitude, sex, and nest fate. Whimbrel may exhibit sex-specific preferences in migration, with males favoring oceanic routes, or molt strategies, with males losing glued-on tags earlier than females. We radio-tracked 45 birds from two study sites 710 km apart, with 30 detected after departure. The northern population departed significantly later than the southern population. Successful males in the north tended to depart later than the other groups. Detection probability declined with time after departure, and males were less likely to be detected than females. Seven females, but no males, were detected in one location for more than 1 day. Birds detected in the Maritime Provinces were not detected farther south, while all other birds were detected farther south along the Western Atlantic coast. This suggests that birds detected in the Maritimes may continue with overwater flights to their wintering areas. Our results are the first to suggest that there may be sex-specific preferences for migration routes, or molt strategies in Whimbrel, implying the need for more complex conservation actions.