Balearic shearwater (Puffinus mauretanicus)

Synonyms: Puffinus puffinus mauretanicus, Puffinus yelkouan mauretanicus
KingdomAnimalia
PhylumChordata
ClassAves
OrderProcellariiformes
FamilyProcellariidae
GenusPuffinus (1)
SizeLength: c. 33 cm (2)

The Balearic shearwater is classified as Critically Endangered (CR) on the IUCN Red List (1).

One of the rarest seabirds in the world, the Balearic shearwater (Puffinus mauretanicus) flies gracefully over the ocean waves with shallow wing-beats on long, slender, stiffly held wings (2) (3). A typically coloured, mid-sized shearwater, the Balearic shearwater is dark brown on the upperside with contrasting brownish-white underparts (3). Two tubular nostrils are situated on the upper bill, a unique feature of the shearwaters, albatrosses and petrels, and the long, thin beak has a slight hook and sharp blades that enable the Balearic shearwater to catch slippery fish after plunge-diving into the water or following an underwater pursuit (4) (5).

From September through late June, the Balearic shearwater is largely found in the Balearic Sea and off the east Spanish coastline. Breeding takes place on the Balearic Islands, with the largest colonies on Formentera and Mallorca, after which the Balearic shearwater migrates northwards to winter off the British Isles and south of the Scandinavian Peninsula (2).

The Balearic shearwater breeds on cliffs and small coastal inlets, and typically returns to the same breeding colony each year (2).

This majestic seabird spends much of its time far out at sea, foraging mainly for herring, sardines and squid. Its prey is caught after a deep plunge into the water from a height of one or two metres, or after a short underwater pursuit (6). Upon catching its prey, the Balearic shearwater will propel itself out off the water with powerful beats of its wings and take flight (7). 

The Balearic shearwater returns to land to breed from February through to June (2). Large colonies of several hundred birds may congregate on sea cliffs and, occasionally, small coastal inlets, where a single, very large white egg is laid under a boulder in a small cave or cavity, with pairs usually reusing nesting sites from previous seasons (2) (6). Breeding pairs typically remain together for many years, with ‘divorces’ occasionally occurring after poor breeding seasons (5). During incubation, and whilst feeding the chick, the parent birds take turns in going out to sea to feed, with foraging birds concentrating on the east coast of Spain to take fish from the productive waters around the Ebro Delta (5) (6). Birds also often take discards from trawlers, which are seen as an easy source of food (6) (8). Retuning to the nest, the chick is fed on a soup of partly digested fish, squid and stomach oil (5). The chick grows quickly and after fledging, the young birds breed for the first time in their third year, living to around 23 years of age (2) (6). 

It is after the breeding season that the Balearic shearwater undertakes its northward migration, following its fish prey to cooler waters. Many thousands of birds gather in the Bay of Biscay, where they may undergo a post-breeding moult, and often birds will travel as far north as the Orkney and Shetland Islands of the British Isles and the southern Scandinavian Peninsula (2) (9).

The Balearic shearwater is the most threatened seabird in the Mediterranean and one of the rarest seabirds in the world (8) (10). Indeed, with an annual decline estimated at around eight percent, this highly threatened seabird could go extinct within the next 40 years (10). At present the greatest threat to the Balearic shearwater is thought to be unnatural adult mortality (11) (12). On land this may be caused by predation by introduced cats, rats and genets (Geneta geneta), and the species may have gone extinct on Cabrera Island as a result (6). At sea this species has a close association with trawlers from which it takes fish discards, and mass mortality has been observed where fish lines have come too close to large groups of birds (2). 

The Balearic shearwater’s breeding habitat is under threat from encroaching urbanisation, as well as degradation from other human activities and introduced rabbits, which compete for nesting sites (2). The species’ foraging habitat is also under threat from pollution, particularly in the Ebro Delta, which has very high levels of mercury that have the potential to accumulate in the birds, causing poisoning and a reduction in reproductive success (2) (6). 

The effects of the loss of its prey are, at present, poorly understood. However, in the 1990s the post-breeding population in the Bay of Biscay appeared to decline, while that in the western channel, several hundred kilometres to the north, become more numerous. The reasons behind this are unclear, but may be due to fisheries affecting the abundance of its prey, or the fish moving northwards in response to climate change, although both these scenarios require re-evaluating (9) (13). Changes in fisheries legislation also have the potential to threaten the Balearic shearwater, as this species has a strong dependency on discards for feeding its chicks during the breeding season (8). 

Additional threats to the Balearic shearwater include attacks by yellow-legged gulls (Larus michahellis), which causes regurgitation and can inflict wounds, as well as hybridisation with the Yelkouan shearwater (Puffinus yelkouan) (2) (6) (12).

Recognising the tragic fate of the Balearic shearwater, the Balearic Government introduced a recovery plan in 1997, which aimed to increase the population and its distribution to all suitable areas of habitat (6). The implementation of this plan has seen the eradication of rats from several nesting sites and the creation of three Special Protected Areas, which protect all nesting areas (2). However, despite these efforts, addressing the high rate of mortality at sea remains a crucial factor in avoiding the extinction of this species (10). This majestic seabird is also benefiting from a large number of studies into its ecology, population size, distribution, priority conservation areas and threats (2).

For more information on the Balearic shearwater, see:

Authenticated (02/06/2010) by Prof. Daniel Oro, Institut Mediterrani d'Etudis Avancats IMEDEA (CSIC-UIB), Mallorca, Spain.
http://www.imedea.uib.es/

  1. IUCN Red List (May, 2010)
    http://www.iucnredlist.org/
  2. BirdLife International (May, 2010)
    http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=30026&m=0
  3. The Royal Society for the Protection of Birds (May, 2010)
    http://www.rspb.org.uk/wildlife/birdguide/name/b/balearicshearwater/index.aspx
  4. Burnie, D. (2001) Animal. Dorling Kindersley, London.
  5. Perrins, C. (2009) The Encyclopedia of Birds. Oxford University Press, Oxford.
  6. Aguilar, J.S. (1999) Species Action Plan for the Balearic shearwater Puffinus mauretanicus in Europe. BirdLife International.
  7. Brooke, M. (2004) Albatrosses and Petrels Across the World. Oxford University Press, Oxford.
  8. Arcos, J.M. and Oro, D. (2002) Significance of fisheries discards for a threatened Mediterranean seabird, the Balearic shearwater Puffinus mauretanicus. Marine Ecology Progress Series, 239: 209-220.
  9. Yesou, P. (2003) Recent changes in the summer distribution of the Balearic shearwater Puffinus mauretanicus off western France. Scientia Marina, 67: 143-148.
  10. Oro, D., Aguilar, J.S., Igual, J.M. and Louzao, M. (2004) Modelling demography and extinction risk in the endangered Balearic shearwater. Biological Conservation, 116: 93-102.
  11. Louzao, M., Igual, J.M., McMinn, M., Aguilar, J.S., Triay, R. and Oro, D. (2006) Small pelagic fish, trawling discards and breeding performance of the critically endangered Balearic shearwater: improving conservation diagnosis. Marine Ecology Progress Series, 318: 247-254.
  12. Genovart, M., Juste, J. and Oro, D. (2005) Two sibling species sympatrically breeding: a new conservation concern for the critically endangered Balearic shearwater. Conservation Genetics, 6: 601-606.
  13. Votier, S.C., Bearhop, S., Attrill, M.J. and Oro, D. (2008) Is climate change the most likely factor of range expansion for a critically endangered top predator in northeast Atlantic waters. Biology Letters, 4: 204-205.