What oceanic seabirds do outside their breeding periods is something of a mystery, although altogether these "sabbaticals' add up to more than half of their lifetime and are probably a key feature of their life history. Here we use geolocation systems based on light-intensity measurements to show that during these periods wandering albatrosses (Diomedea exulans) leave the foraging grounds that they frequent while breeding for specific, individual oceanic sectors and spend the rest of the year there — each bird probably returns to the same area throughout its life. This discovery of individual home-range preferences outside the breeding season has important implications for the conservation of albatrosses threatened by the development of longline fisheries.
On 26 October 1999, a wandering albatross of at least 50 years old was found dead on a beach in New South Wales, Australia (Fig. 1 ). A ring identified the bird as coming from the Crozet Islands, 7,900 km away in the Indian Ocean; this bird was originally banded in September 1960 as an adult (over 10 years old) a few kilometres from the site of its death. This recovery of a bird after 40 years, together with the successive recapture every second year of several individuals from Crozet at the same site1, suggests that wandering albatrosses, which breed every second year, may return routinely throughout their lifetime to a particular place during the non-breeding year.
Figure 1: Oceanic sectors used by two male (mauve dots and blue triangles) and two female (red dots and yellow squares) wandering albatrosses, as studied by geolocation.
The dots indicate two partners of the same pair. Two locations are estimated for each bird per 24-h cycle. Arrow indicates the recovery site of ringed birds off New South Wales, Australia; green circle, the Crozet Islands.
High resolution image and legend (38K)It has been assumed that these birds wander aimlessly during their biennial sabbatical year, circumnavigating the Southern Ocean by riding the wind2, 3, visiting places like the waters of New South Wales en route. The question of where these birds spend half of their life is important (Fig. 2), not only because this species may potentially exploit almost any area in the Southern Ocean4, but also because wandering albatrosses, like many other albatrosses and petrels, are threatened by longline fisheries in the Southern Ocean. They are killed in tens of thousands while scavenging for baited hooks and from drowning when lines are set5. Any plan to remedy this shocking loss will depend on establishing the extent of overlap in the areas used by both albatrosses and fisheries.
Figure 2: The wandering albatross spends more than 95% of its life in the open ocean, ten years of this as as an immature bird, but also half of its mature life during its non-breeding years.
Birds move to specific oceanic areas far from their breeding grounds; area preferences appear to last a lifetime.
High resolution image and legend (42K)Using satellite telemetry to study the movements of seabirds over a complete year is difficult and costly. Instead, we determined bird position using loggers weighing 20 g that record light intensity and are attached to a ring on the bird's leg. We were able to estimate the local time of dawn and dusk, determined by light thresholds, with respect to Greenwich Mean Time using a precise internal clock: after consideration of the date, the day length could be used to determine the latitude, and the longitude was determined from local time of noon6, 7, 8.
We fitted nine wandering albatrosses on the Crozet Islands with loggers during February–March in 1995 and 1996, just after a failed breeding attempt and before their departure from the breeding grounds for a year. This pattern of absence from the breeding grounds is similar to that adopted by birds that complete a successful breeding season in December1. All tagged birds returned one year later with the unit intact, although only four devices provided light measurements over 6 months or more.
After leaving the island, the four birds (two males and two females) flew to a specific ocean sector where they overwintered, returning to their breeding place in late December. These sectors ranged from tropical and subtropical waters (the females) to sub-Antarctic and Antarctic waters (the males) at distances 1,500–8,500 km away from Crozet. In each pair, the male spent the winter just north of the pack ice in Antarctic waters, whereas the female stayed south of Madagascar.
To our knowledge, this is the first time that the wintering zones of a pelagic seabird have been studied remotely. Our results provide surprising evidence that wandering albatrosses do not wander around the Southern Ocean during their non-breeding year. After spending a year covering an estimated 150,000 km foraging around colonies to hatch and raise their single chick4, 9, wandering albatrosses take a year off. The vast distances covered during breeding increase the probability of encountering dispersed prey while effectively using the wind to reduce flight costs9. During the sabbatical year, the birds have lower energy requirements and are not restricted to a central breeding place.
But even with this new freedom, the birds confine their movements to a preferred sector, not only because of their reduced energy requirements but maybe also because at this time they undergo a partial moult of their flight feathers. Moulting probably reduces flight efficiency and therefore increases flight costs. Also, by moving away to a distant ocean sector far from the breeding grounds, the competition between the element of the population in its breeding year and the other in its sabbatical year is reduced. Information from banding indicates that birds use the same wintering zone from year to year, probably throughout their lifetime. The wintering grounds favoured by each individual in the open ocean may be visited repeatedly because the birds learn over years the location of profitable feeding zones.
Our results have important implications for the conservation of this threatened species10. During the breeding season, females favour the subtropical waters north of Crozet where tuna fisheries are located, whereas males prefer the colder waters at higher latitudes where fisheries for toothfish have been developed11. Birds spending their sabbatical year in sectors where long-line fisheries occur are at risk of being killed. This bizarre selection pressure, dependent perhaps on the whims of juvenile choice, means that only those wintering in zones without fisheries will survive in the long term. We now need to find out what factors lead to selection of sabbatical areas in the first place. In the meantime, we have to accept that even during their sabbaticals adult birds are unlikely to change their habits to avoid the dangers from fisheries.