Extreme variation in migration strategies between and within wandering albatross populations during their sabbatical year, and their fitness consequences

Abstract

Migratory behavior, routes and zones used during the non-breeding season are assumed to have been selected to maximize fitness, and can lead to genetic differentiation. Yet, here we show that migration strategies differ markedly between and within two genetically similar populations of wandering albatross Diomedea exulans from the Crozet and Kerguelen archipelagos in the Indian Ocean. Wandering albatrosses usually breed biennially if successful, and during the sabbatical year, all birds from Kerguelen migrate to the Pacific Ocean, whereas most from Crozet are sedentary. Instead of taking the shortest routes, which would involve a return against headwinds, migratory birds fly with the westerly winds, requiring detours of 10,000 s km. In total, migrants circumnavigate Antarctica 2 to 3 times, covering more than 120,000 km in a single sabbatical year. Our results indicate strong links between migratory behavior and fitness; all birds from Kerguelen breed biennially, whereas a significant proportion of those from Crozet, especially females, are sedentary and breed in consecutive calendar years. To breed annually, these females temporarily change mate, but return to their original partner in the following year. This extreme variation in migratory behavior has important consequences in term of life history evolution and susceptibility to climate change and fisheries.

Figure 1. Kernel densities or utilisation distributions (25%, 50% 75% and 95% UDs) of adult wandering albatrosses tracked during the sabbatical year from Crozet (red dot) and Kerguelen (blue dot).

The 95% UD of breeding birds is indicated by the solid line for each population (Figures produced from R software).

Figure 2. The three main strategies used by wandering albatrosses during sabbatical years, sedentary, sedentary with distant incursions of two Crozet birds, and migratory with two consecutive circumpolar movements of a Kerguelen bird: after an initial rapid flight to Chilean waters where the bird spent 2 months, it moved eastward through the Atlantic and the Indian Ocean (yellow track) to reach the Chatham Rise, east of New Zealand, before returning to Kerguelen (orange track) through the Pacific and Atlantic (Figure produced from Sigmaplot).

Figure 3. Proportion of migratory birds from Crozet and Kerguelen in the different oceanic sectors of the Southern Ocean over the annual cycle of the sabbatical year (Figure produced from Statistica).