Fantastic Journey

Illustration prepared by Frank Knight and taken from Fantastic Journeys - The marvels of Animal Migration edited by R. Robin Baker 1991. Merehurst: London 240pp [ISBN 1-8539-185-2].

In this book this diagram accompanied the text on Seabirds by Peter Fullagar (pp 88-95). At the time of publication in the early 1990s there was still debate about the extent to which the Short-tailed Shearwater Ardenna tenuirostris occurred in Antarctic waters during the breeding season. Shortly after publication it was established beyond doubt that this is indeed the main summer feeding area for breeding birds of this species and also for the Sooty Shearwater A. grisea. They both commute to and fro between their nest sites and the Antarctic pack ice region throughout the southern summertime.

The mythical figure-of-eight migration route for the Short-tailed Shearwater (so often shown in publications before this time) was deliberately not perpetuated! In fact, we now know (from GPS tracking of individuals using data-loggers attached year round) that for the Sooty Shearwater the annual trans-equatorial migration of adult breeding birds is more complex in that they move either directly to the north Pacific or circle up towards the Bering Sea via the west coast of the Americas. They also favour more than one 'overwintering' area in the north Pacific during this annual migration but they all, nevertheless, return via the central Pacific to their main breeding areas in New Zealand. Some breeding pairs migrate along the same general route as each other but others are as likely to head off independently and do not necessarily overwinter in the same area with their mates. Short-tailed shearwaters probably do much the same except there is no real evidence that many (or for that matter any) would head towards the eastern Pacific where they are considered to be extremely rare. It is most likely that Short-tailed Shearwaters take a great circle route to and from the North Pacific during this annual migration by adult breeding birds.

It is still not clear what pre-breeding Short-tailed or Sooty Shearwaters do on migration. Some Sooty Shearwaters may remain in the southern hemisphere year round although there is little evidence that Short-tailed Shearwaters do the same but some of the younger birds of both species may also remain in north Pacific waters and not return south during the southern summer.