01/01/2010
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Manx and Balearic Shearwaters

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Key featured species

  • Balearic Shearwater Puffinus mauretanicus
  • Manx Shearwater Puffinus puffinus
  • Sooty Shearwater Puffinus griseus
  • Yelkouan Shearwater Puffinus yelkouan
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The problem

Balearic Shearwater has to be separated from the similar-sized and much more common Manx Shearwater. Darker individuals also need to be distinguished from the larger Sooty Shearwater, which is a late summer and autumn visitor to our coasts from its breeding islands in the southern hemisphere.

The solutions

Size and shape

In size and shape Balearic Shearwater resembles Manx Shearwater, although in fact it averages about 10 per cent larger. It is also bulkier, particularly about the head and neck, and has a shorter tail with the feet projecting beyond. In direct comparison, the wings are slightly longer than those of Manx but, proportionately, they are in fact slightly shorter, producing a somewhat more ‘fluttery’ flight action.These differences are best appreciated when the two species are seen together: Balearic looks positively thick-set and stocky in direct comparison to Manx.

Plumage

This is notoriously variable. In comparison with the clean cut, smartly contrasting black-and-white Manx, most Balearics are brown and rather ‘messy’.The brown upperparts of late summer adults are also prone to fading and bleaching, much more so than Manx, which has a more stable black pigment (Yésou et al 1990). Worn birds may show a paler collar around the back of the neck as well as patchy plumage on the upperparts. The head, breast, flanks, undertail coverts and vent are brown and this merges in a dull and smudgy way with the rest of the underparts, which are a rather dusky whitish. Balearic also shows some brown at the base of the underwing and axillaries.A minority of Balearics are more extensively white below, resembling Yelkouan Shearwater (the eastern Mediterranean species yet to be confirmed in Britain – see below) and when faced with paler individuals bear in mind that some Manx can appear distinctly brown-toned above, particularly in bright light.

Ageing

From June to September, juveniles can be distinguished by their darker, fresh and immaculate plumage at a time when adults are often worn and showing traces of moult. Like the adults, juveniles also show variations in their plumage tones but they average darker. Pale juveniles are apparently scarce. As autumn progresses, ageing becomes increasingly difficult as the adults approach the end of their moult, which is completed by October (Yésou et al 1990).

Confusion with Sooty Shearwater

More confusingly, some Balearics are peculiarly dark, with a limited dusky patch being confined to the central belly and thus invisible when sitting on the water. Such birds may be confused with Sooty Shearwater.The latter, however, as well as being 15-20 per cent larger, has a rather fat body and narrow wings that are typically angled back from the carpals, creating a fat-bodied, thin-winged ‘mini albatross’ shape. In addition, Sooty appears all-dark below and, in good light, shows quite distinctive silvery underwings. Balearic’s underwings are, depending on light and individual variation, either whitish, greyish or silvery, with a thick dark trailing edge. In stormy conditions, Sooties tend to ‘bound’ across the sea in a series of high arcs. Balearics typically fly closer to the surface with their more ‘fluttery’ flight action and stiffer-looking wings.

Status

As its name suggests, Balearic Shearwater breeds in the Balearic Islands, where it has suffered a well-documented population crash mainly as a consequence of predation by Black Rats and domestic cats. Its current breeding population is estimated at only 2,000 pairs and it is now listed as Critically Endangered.

After breeding, a large proportion of the population disperses westwards out of the Mediterranean and into the Atlantic. There, the birds have traditionally gathered to moult in late summer in northern and central parts of the Bay of Biscay, where they feed close inshore on pilchards and anchovies. In the last decade or so it seems that this moulting population has shifted northwards, with larger numbers being recorded in the western English Channel. This change is thought to relate to increased surface sea temperatures, which in turn are likely to be a consequence of global warming (Wynn et al, from the internet, and Yésou 2003).

Paradoxically, therefore, sightings of the species are increasing in Britain at a time when its breeding population is declining. Numbers of Balearic Shearwaters reaching our shores are, however, notoriously variable and prone to periodic influxes. Most are seen in the English Channel, where Portland Bill in Dorset is a prime site. Smaller numbers penetrate into the North Sea, the Irish Sea and even to the west coast of Scotland. It is much more of an inshore feeder than many of its relatives and, to see the species, try seawatching from any decent headland between July and October (although occasional birds are seen at other times, even in winter). Observers are encouraged to submit all records of Balearic Shearwaters to county recorders. Clearly we have an international duty to monitor this species and this is a case where individual observers really can contribute to our understanding and, ultimately, to the conservation of this important European species.

Taxonomy

It is difficult to discuss Balearic Shearwater without reference to both its status and taxonomy. Traditionally, it has been treated as a Mediterranean race of Manx Shearwater but, in 1991, the two Mediterranean races – the western mauretanicus and the eastern yelkouan – were split from Manx as ‘Mediterranean Shearwater’. Then, in 2000, these two forms were split from each other into Balearic Shearwater and Yelkouan Shearwater (the latter is also sometimes referred to as ‘Levantine Shearwater’). This explains inconsistences in its name, and bear in mind that the recent split has not yet been reflected in most field guides, including the excellent Collins Bird Guide. For more information on Yelkouan Shearwater, see Birdwatch 134: 27-30.



References

  • Wynn, R B, Yésou, P, and Josey, S. The changing status of Balearic Shearwater Puffinus mauretanicus in north-west European waters: relationships to sea temperatures, phytoplankton concentrations and fish abundance. Presentation abstracts of the Second International Manx Shearwater Workshop, from the internet: www.habitas.org.uk.
  • Yésou, P. 2003. Recent changes in the summer distribution of Balearic Shearwater Puffinus mauretanicus off western France. Scientia Marina 67: 143-148.
  • Yésou, P, Paterson, A M, Mackrill, E J, and Bourne, W R P. 1990. Plumage variation and identification of the ‘Yelkouan Shearwater’. British Birds 83: 299-319.