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Each year hundreds of millions of birds cross the Atlantic Ocean during the peak of tropical cyclone activity. The extent and consequences of migrant-storm interactions remain unknown. We tracked whimbrels from two populations (Mackenzie Delta; Hudson Bay) to examine overlap between migration routes and storm activity and both the frequency and consequence of storm encounters. Here we show that Mackenzie Delta and Hudson Bay whimbrels follow different routes across the ocean and experience dramatically different rates of storm encounters. Mackenzie Delta whimbrels departed North America from Atlantic Canada, made long ( x ¯ = 5440 ± 120.3 km) nonstop flights far out to sea that took several days ( x ¯ = 6.1 ± 0.18) to complete and encountered storms during 3 of 22 crossings. Hudson Bay whimbrels departed North America from the south Atlantic Coast, made shorter ( x ¯ = 3643 ± 196.2 km) nonstop flights across the Caribbean Basin that took less time ( x ¯ = 4.5 ± 0.29) to complete and encountered storms during 13 of 18 crossings. More than half of Hudson Bay storm encounters resulted in groundings on Caribbean islands. Grounded birds required longer ( x ¯ = 30.4 ± 5.32 days) to complete trans-Atlantic crossings and three were lost including 2 to hunters and 1 to a predator. One of the Mackenzie Delta whimbrels was lost at sea while crossing the Intertropical Convergence Zone. Whimbrels use two contrasting strategies to cross the Atlantic including (1) a long nonstop flight around the core of storm activity with a low likelihood of encountering storms but no safety net and (2) a shorter flight through the heart of Hurricane Alley with a high likelihood of encountering storms and a safety network of islands to use in the event of an encounter. Demographic consequences of storm encounters will likely play a role in the ongoing evolution of trans-Atlantic migration pathways as global temperatures continue to rise. [ABSTRACT FROM AUTHOR]

Migrant shorebirds operate within a series of landscapes and must adjust their daily activities to achieve seasonal time and energy objectives. Night roosts are essential landscape elements that provide safety from predators for many shorebird species. What costs migrants incur to use night roosts and how these costs vary across staging sites are poorly understood. We tracked 42 adult whimbrels Numenius phaeopus with satellite transmitters and used night locations to delineate 39 night roosts during spring and fall migration. We used daytime locations to measure round‐trip commuting distances between night roosts and foraging areas and estimated daily commuting costs including distance, time and metabolic energy expenditure. We identified night roosts on offshore islands (n = 20) and onshore locations including along habitat edges (n = 13) and on topographic highs within extensive marshes (n = 6). Mean daily commuting costs varied between roosts. Whimbrels took 3.9–52.1 min (median = 15.2) to fly 3.1–42.2 km (median = 12.3) which costs 6.1–82.4 kj (median = 22.3) in lean mass energy expenditure and 8.1–109.2 kj (median = 31.5) in leaving mass energy. Birds using offshore roosts had twice the commuting distance and associated costs compared to those using onshore roosts. The contribution of commuting costs to the premigratory energy budget ranged from 1.5 to 18.8% with costs for nearly 30% of roosts exceeding 10%. Commuting costs to and from night roosts appear to be biologically relevant within some staging sites and should be considered among other constraints faced by migrants during stopover periods when food or time is limiting. [ABSTRACT FROM AUTHOR]

For most shorebird species, our understanding of the basic limiting factors and when or where they operate during the annual cycle is currently inadequate to either understand ongoing declines or effectively allocate conservation resources for recovery. Whimbrels (Numenius phaeopus) exhibit delayed recruitment and have low fecundity, and populations with such life-history traits are often vulnerable to increases in adult mortality. We tracked 33 adult Whimbrels with satellite transmitters for 12,802 bird-days to investigate patterns in survival and recorded 16 probable and 5 confirmed mortalities. We used Cox's proportional hazards model to estimate daily hazard rates by season and a Kaplan-Meier product limit estimator to estimate monthly survival. Daily hazard rates varied by season and were 5 times higher during migratory periods (fall and spring migration) compared to stationary periods (winter and breeding). Estimated annualized survivorship was 0.54 ± 0.21 (SE) and on the lower end of the range of 0.8–0.9 believed to be required to maintain a stable population. More than half of the mortality recorded during the study occurred during the fall hunting season and within the last remaining area throughout the Western Hemisphere where significant legal and illegal hunting occurs. One-third of mortality occurred during spring migration either within terminal staging sites or as birds made final movements to breeding grounds. Survival during the migratory periods may have been influenced by the use of transmitters. [ABSTRACT FROM AUTHOR]