Global marine flyways identified for long-distance migrating seabirds from tracking data

Aim: To identify the broad-scale oceanic migration routes (‘marine flyways’) used by multiple pelagic, long-distance migratory seabirds based on a global compilation of tracking data.

Location: Global

Time period: 1989 – 2023

Major taxa studied: Seabirds (Families: Phaethontidae, Hydrobatidae, Diomedeidae, Procellariidae, Laridae and Stercorariidae)

Methods: We collated a comprehensive global tracking dataset that included the migratory routes of 48 pelagic and long-distance migrating seabird species across the Atlantic, Indian, Pacific and Southern Oceans. We grouped individuals that followed similar routes, independent of species or timings of migration, using a dynamic time warping clustering approach. We visualized the routes of each cluster using a line density analysis and used knowledge of seabird spatial ecology to combine the clusters to identify the broad-scale flyways followed by most pelagic migratory seabirds tracked to-date at an ocean-basin scale.

Results: Six marine flyways were identified across the world’s oceans: the Atlantic Ocean Flyway, North Indian Ocean Flyway, East Indian Ocean Flyway, West Pacific Ocean Flyway, Pacific Ocean Flyway, and Southern Ocean Flyway. Generally, the flyways were used bi-directionally, and individuals either followed sections of a flyway, a complete flyway, or their movements linked to two or more flyways. Transhemispheric figure-of-eight routes in the Atlantic and Pacific oceans, and a circumnavigation flyway in the Southern Ocean correspond with major wind-driven ocean currents.

Main conclusions: The marine flyways identified demonstrate that pelagic seabirds have similar and repeatable migration routes across ocean-basin scales. Our study highlights the need to account for connectivity in seabird conservation and provides a framework for international cooperation.

Methods
We collated and standardised seabird tracking data for pelagic, long-distance migratory species according to previously developed protocols (Carneiro et al., 2020). We assigned the annual life cycle stage to each location, and only those recorded during migration were used in our analyses. We processed and filtered tracking data to exclude individuals that did not meet a set of criteria. Individuals were then grouped based on the shape of the migratory route, irrespective of species identity or the timing of migration. We estimated line densities for each cluster of individuals and the results were smoothed and combined where appropriate to delineate a network of marine flyways.