Balearic Shearwater - Analysis of Strumble Head records

Puffinus mauretanicus

From one to five birds per occasion were recorded from Skokholm, Skomer, Grassholm, Ramsey,

Whitesands Bay, St David’s Head, Fishguard Bay, St Govan’s Head, from the Rosslare to Fishguard ferry and in the Celtic Deep area. However intensive watching at Strumble Head revealed a greater presence in local waters than observations elsewhere hitherto suggested.  

The annual totals are probably over-estimates as they would include individuals remaining in the observation area for more than one date. Unlike most other seabirds which are generally seen passing north to south through local waters in the autumn, Balearic Shearwaters arrive from the south in search of food and are often seen feeding offshore.

Hours of observation

 

The number seen has varied from year to year.  The hours of observation compared with birds seen indicates that this was not just a consequence of observer effort. The trend over the 23 year period was of increase.

This was part of an increase noted throughout south west Britain at this time, demonstrated by Wynn and Yesou (2007), which was probably due to a warming of the sea surface causing small fish shoals, the prey of this species, to move  further north than in the past.

Most were recorded between July and November, the largest numbers between August and October. Counts at Strumble Head have usually consisted of one to six birds per day but rising to about 20 when strong northerly winds blew. Higher counts of 33 on the 4th October 1996, 36 on the 2nd October 1999, 37 on the 22nd September 2003 and the maximum recorded of 93 on the 7th October 2006, occurred when there were strong northerly winds, which pushed birds closer inshore than they might otherwise have approached. Exceptional numbers of Balearic Shearwaters were seen in the waters of south west Britain including Wales, in the autumn of 2006.

Patterns of occurrence at Strumble Head: total numbers.

 There have been a few sightings outside the July to November period: once at the Smalls in December 1984 and January 1983, 10 times in eight different years at Strumble Head in December and 10 times in four years in January. None have been recorded in March but singles have been noted at Skomer on the 25th April 1991, at Skokholm on the 15th May 1997, from the Fishguard to Rosslare ferry on the 25th May 1997, near Grassholm on the 2nd June 1993, off Strumble Head on the 2nd February 2002, 16th April 1990, 2nd June 1993, 2nd June 1996 and 8th June 1987. 

From time to time observers have pointed out that some shearwaters seen in Pembrokeshire waters resemble Yelkouan Shearwater. Other observers considered these birds could be particularly pale Balearic Shearwaters. Those breeding on Manorca would appear to exhibit mixed characteristics of both Balearic and Yelkouan Shearwaters, further clouding the issue.

Graham Rees

(Covers records up to and including 2006)

References

WYNN. R. And YESOU. P. 2007. The changing status of Balearic Shearwater in northwest European waters, British Birds, Vol. 100, 392 – 406.