Species Spotlight - Manx Shearwater, the 'Manxie'

Manx Shearwater, © Steve Round

A glimpse of a Manxie speeding past our coast is always an exciting moment. With it's characteristic up and down side to side flight, one second in a wave trough, the next sweeping upwards in a large glide followed by rapid beats of the wings. They are usually a fair distance out and can be difficult to spot at first, especially during a gale. But once you get your eye in during a strong west wind it can be surprising just how many are steadily making their way through Liverpool Bay.

One of my favourite books is ‘The Island’ by Ronald Lockley; here he describes his life on the lonely island of Skokholm, Pembrokeshire, in the 1930s. At a time when little was known about the breeding habits of sea birds RL spent 10 years studying the birds of Skokholm, in particular the Manx Shearwater. He expands on the subject of Manx Shearwaters in the monograph 'Shearwaters', long recognised as a classic in scientific nature writing. Even after all these years and many other studies since the fact that his name is mentioned ten times in the Manx Shearwater account in the Birds of the Western Palearctic and four times in the BTO Migration Atlas shows how important his work was. It was he who discovered the remarkably long breeding season of this species with an incubation period of c51 days and the fledging period of c70 days. He also discovered that the adult birds could be away from the nest several days at a time and that many travel long distances away from the breeding colonies in their search for food. This, of course, has a large bearing on trying to determine the origins of birds we see off the Dee Estuary out in Liverpool Bay.

Manx Shearwater off north Wirral during gales in 2004, © Steve Round

Currently Skokholm has at least 46,000 pairs nesting each summer, and the nearby island of Skomer a remarkable 100,000. The combined total of breeding pairs on these islands makes them easily the most important site in the world for this species with c45% of the world's population. It is likely that many of the birds we see here are from these two islands; Liverpool Bay is only an easy 12 hour flight away for this fast flying species. The island of Rhum in Scotland also has large numbers of Manx Shearwaters breeding with c36% of the world's population and, although further than South Wales, Liverpool Bay is easily within foraging range. RL found from ringing recoveries that they could fly as much as 600 miles from the nesting site during a feeding trip.

The histogram above (based on Hilbre and north Wirral records) demonstrates that a peak is reached in June followed by a smaller peak in late summer/autumn. The peak in June coincides with the period of egg incubation and it is typical during this period for each parent to be away from the nest for about five days, each taking turns at sitting on the egg. Five days would be ample time for a few circuits around the Irish Sea. This is followed by a sudden drop off in numbers when the adults are feeding the chick; they return to the nest more often at this time and therefore do not range so widely. By the end of August migration will have begun and there is probably also some post-breeding dispersal prior to their southward movement. If there is a strong north-west wind in September many Manx Shearwaters get blown in to Liverpool Bay within sight of land and it is probable that a lot of these are Scottish breeders blown in through the North Channel in to the Irish Sea. During September and October the majority of birds will make their way rapidly to the South Atlantic off the east coast of South America where they spend the southern summer; very few are seen in the Irish Sea after mid-October. However, a few do spend the winter north of the equator and this explains the presence of one observed off Hoylake during strong south-west gales on Dec 9th 2006, the latest ever sighting for Cheshire and Wirral.
On the rare occasions we do get large numbers of Manx Shearwaters within viewing distance of the coast it is a spectacular sight. It is well worth searching through these large flocks of Manxies as they may well contain a rarer shearwater or two. The max numbers for Hilbre/North Wirral over the past thirty years are shown in the histogram below and, not unexpectedly, shows a lot of variation from year to year. The 720 counted on June 23rd 2000 off Hoylake is the highest ever count recorded for Wirral.