Bingo! full house on shearwaters
By Mark Tasker
For the first half of this cruise (north and west of Britain and Ireland), we were lucky enough to have Mark Lewis and Paul French as our on-board bird observers. Since they stepped ashore, we have only been able watch birds informally. The Bay of Biscay has lower densities of all species except perhaps European storm-petrel than the north-west approaches, but its bird fauna is different. This is perhaps best demonstrated by the differing set of shearwater species. We have seen all six species that are reasonably feasible in NW European waters – a full house!
North of Ireland and west of Scotland, wee saw many Manx shearwaters – their main breeding colony here is on Rum in the Inner Hebrides, but there are smaller colonies also, such as St Kilda. We know that most of the birds from these colonies remain to forage reasonably close to home, but some may be seen out in the Atlantic.
Many shearwaters migrate between the hemispheres during the year; so it is for the second species seen predominantly in the northern sector. Sooty shearwaters breed in the South Atlantic on, for example, the Falkland Islands. It seems that their migration route take them northwards in the west Atlantic, before crossing to the east and making their way southwards. We found most of these birds on the Rockall Bank, perhaps freshly arrived from their transatlantic crossing.
Our southern survey section was far offshore in the Bay of Biscay, venturing inwards towards France and the UK. The second long distance migrant shearwater visiting the northern hemisphere in its non-breeding season was seen soon after we left Cork. Great Shearwaters breed in the Tristan da Cunha archipelago but tend not to venture as far north as sooty shearwaters, perhaps reflecting the warmer waters of their breeding sites compared to the sub-Antarctic home of the sooties.
The final three shearwaters all breed in less remote locations. Cory’s shearwater breeds in Madeira, the Azores and the Canary Islands and is the commonest seabird in the offshore Bay of Biscay at this time of year, its long languid flying posture with wings held slightly bowed downwards was always a welcome sight – groups of them can signal the presence of (apparently) feeding common dolphins.
Balearic shearwaters breed (surprise!) on the Balearic islands in the Mediterranean but venture out into the Atlantic in the non-breeding period. There they occur in highest numbers on the inshore parts of the Bay of Biscay off France, with relatively few venturing northwards to waters off SW England. The species is classified as Critically Endangered (due mostly to pressures on or near their breeding colonies) so it was a pleasure to see three of these birds – they look like a browner and smudgy version of Manx shearwater on the southernmost legs of the survey.
The final shearwater seen was a Baroli shearwater – this smaller bird breeds also on the Azores, Madeira and Canary Islands but visits western Iberia particularly. The Bay of Biscay is at the northern edge of its range. The one bird seen took off from the water on small rounded wings rather like some of the auks at a position almost as far west as the survey went in international waters. We saw another in the northern part of France’s offshore waters.