Length: 34 – 39 cm
Wingspan: 78 – 90 cm
Weight: 472-565 g
Appearance: medium-sized seabird with contrasted belly and back, fine beak and marked angle with the head.
Distinguishing characteristics: less contrasted than Yelkouan Shearwater.
Flight: typically « shearing » flight dipping from side to side on stiff wings with few wingbeats, the wingtips almost touching the water.
Sound: silent at sea but colonies are noisy at night, with raucous cackling calls.
Ecology and habitat
Nest: breeds on offshore islands and coastal cliffs and nests in burrows which are only visited at night to avoid predation.
Diet: feeds on fish (anchovies, sprats and sardines), mollusks, discards from fishing boats.
Behaviour at sea: gregarious, can be seen in large numbers from boats or headlands
* This map indicates coastal nesting sites in the Mediterranean and adjacent Seas.
Distribution and movement
Breeding: only in the Balearic islands.
One mixed breeding colony of both Yelkouan and Balearic Shearwaters has been reported on Minorca.
Wintering: in the Atlantic, crossing the Strait of Gibraltar, headed by the non-breeders moving north towards the productive coasts of Portugal. Many Balearic Shearwaters migrate north in summer to feed in seas off the British Isles and south of the Scandinavian Peninsula.
Phenology: pre-laying: January-February. Incubation: March-April, during 48-52 days. Chick-rearing: May-June, during 65-70 days. Fledging: mid-June to early July.
Global population estimate: 24,000 – 26,500 individuals leave each year the Mediterranean through the Strait of Gibraltar. Relatively small population which is undergoing an extremely rapid decline, largely related to low adult (and immature) survival rates.
Threats: lack of breeding habitat, predation when breeding (including introduced mammals), bycatch, pollution (including light pollution) and fish stock depletion.
Protection level: Barcelona Convention : Annex II; Bern Convention : Annex II; Birds Directive : Annex I; IUCN Red List: Critically Endangered.
Some key references
Arcos JM et al. (2012). New estimates at sea suggest a larger global population of the Balearic Shearwater Puffinus mauretanicus. Proceedings of the 13th Medmaravis Pan-Mediterranean Symposium (pp. 84-94).
Arroyo GM et al. (2014) New population estimates of a critically endangered species, the Balearic Shearwater Puffinus mauretanicus, based on coastal migration counts. Bird Conservation Int 26:87-99.
Austin RE et al. (2019) Patterns of at-sea behaviour at a hybrid zone between two threatened seabirds. Scientific reports, 9(1), 1-13.
Louzao M. et al. (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.