Migratory shorebirds face many threats throughout their migration from Arctic breeding areas to wintering sites and back again. This is especially true for the rufa subspecies of the Red Knot (Calidris canutus rufa). Each year red knots migrate up to 20,000 miles from Arctic breeding grounds. Breeding success largely depends on the condition and arrival time of shorebirds at the breeding grounds. For this reason, the rufa red knot relies heavily on stopover locations on the northbound return flight, especially Delaware Bay. Previously, it was believed that arrival and departure time from southbound stopover sites were less strict, as the need to migrate south was less dependent on timing. However, recent work conducted by our team in partnership with the USFWS has shown red knots face the same timing restrictions during their fall migration. Needing to get to their long-distance wintering location before the raptor migration to avoid predation and to molt, further protection of these sites is a key element to their survival and recovery.
While conditions in the Delaware Bay may have been a key driver of the red knot population decline, knots and many other shorebird species face multiple and interacting threats throughout their annual cycle that impact population trajectories. Understanding threats to important stopover sites is key to recovering Red Knot and other shorebird populations. While considerable attention has been focused on understanding the northward migration stopovers because of their influence on breeding success, there has been far less attention to the southward migration. Yet they must make the same long-distance migration and may encounter similar bottlenecks in the need for intense, short-term foraging opportunities.
Both Cape Cod, Massachusetts and the Atlantic Coast of New Jersey are important southbound stopover sites for migratory shorebirds during their fall migrations. However, the value of these Atlantic Coast sites is poorly understood and therefore the management of threats to key stopover sites is poor. Yet recent work has shown knots doubling body weight to make oceanic flights in much the same pattern as the spring flight. Over the last decade, our team's studies suggest red knots employ multiple migratory strategies to make their southbound migration and avoid key threats. Knots must either gain weight quickly and leave stopovers before the migration starts or remain in the stopovers until the raptor migration ends. While in the stopover, knots must evade people, especially in August, the height of summer recreational. Once departing, they will have to navigate through increased tropical storm caused by climate change. Over the next decade, knots will have to navigate an increasing number of already planned offshore wind turbines. With red knots facing heavy threats and similar timing restrictions during their southbound migration as on their northbound migration, further protection of these sites a key element to their survival and recovery.