Whimbrel populations differ in trans-atlantic pathways and cyclone encounters

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) over bar = 5440 +/- 120.3 km) nonstop flights far out to sea that took several days ((x) over bar = 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) over bar = 3643 +/- 196.2 km) nonstop flights across the Caribbean Basin that took less time ((x) over bar = 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) over bar = 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.

Automated summary

Each year, hundreds of millions of birds cross the Atlantic Ocean during peak tropical cyclone activity, with whimbrels from the Mackenzie Delta and Hudson Bay populations tracked to examine migration routes and storm encounters. The study found that the two populations follow different routes and experience varying rates of storm encounters, with Hudson Bay whimbrels more likely to encounter storms and ground on Caribbean islands. The demographic consequences of these storm encounters may impact the evolution of trans-Atlantic migration pathways as global temperatures rise.