Balearic shearwater

Balearic shearwater
Name	Balearic shearwater
Status	CR
Status system	IUCN3.1
Genus	Puffinus
Species	mauretanicus
Authority	(P. R. Lowe, 1921)
Range map caption	Breeding range (red) and non-breeding range (blue)

Balearic shearwater. It is a medium-sized seabird endemic to the Balearic Islands in the western Mediterranean Sea. Classified as Critically Endangered by the International Union for Conservation of Nature, it faces severe threats from fisheries bycatch and introduced predators. The species is known for its characteristic flight, low over the water, and its seasonal migrations into the Atlantic Ocean.

Taxonomy and Systematics

The species was first described by British ornithologist Percy Roycroft Lowe in 1921. It was long considered a subspecies of the Manx shearwater or the closely related Yelkouan shearwater. Genetic studies, including analyses of mitochondrial DNA, led to its recognition as a distinct species within the genus Puffinus. Its closest relative is the Yelkouan shearwater, with both species forming a clade separate from the Atlantic populations of Manx shearwater. The scientific name Puffinus mauretanicus references the ancient Roman province of Mauretania, though its breeding range is confined to the Spanish archipelago.

Distribution and Habitat

This seabird breeds exclusively on coastal cliffs and islets in the Balearic Islands, primarily Mallorca, Menorca, Ibiza, and Formentera. Outside the breeding season, it disperses widely, moving through the Strait of Gibraltar into the eastern Atlantic Ocean. Its non-breeding range extends north to the Bay of Biscay and the British Isles, and south along the coasts of Portugal, Spain, and Morocco. It is highly pelagic, spending most of its life over deep, offshore waters, only coming to land to nest.

Physical Characteristics

The Balearic shearwater is approximately 30–38 centimeters in length with a wingspan of 75–90 centimeters. Its plumage is predominantly brownish-grey above and whitish below, with indistinct boundaries between the colors. It has a slender, grey bill with a dark tip and pale pinkish legs. In flight, it shows a characteristic shearwater profile with stiff, straight wings and a low, banking flight over wave troughs. It can be distinguished from the similar Yelkouan shearwater by its slightly larger size, slower wingbeats, and generally darker underwings.

Behavior and Ecology

It is a gregarious species, often forming flocks, especially during migration and at productive feeding grounds. Its diet consists mainly of small pelagic fish such as anchovy and sardine, as well as cephalopods and crustaceans, which it captures by plunge-diving or surface-seizing. It is often attracted to fishing vessels and is vulnerable to bycatch in longline and gillnet fisheries. Key predators at breeding colonies include introduced rats and feral cats, while at sea it may be preyed upon by large gulls and skuas.

Conservation Status

Listed as Critically Endangered on the IUCN Red List, it is one of Europe's most threatened birds. The primary threats are incidental mortality in fishing gear, predation by invasive species at nesting sites, and marine pollution. Conservation efforts are coordinated by organizations like BirdLife International and the Spanish government, focusing on rat eradication programs on key islets, promoting fisheries mitigation measures, and monitoring population trends. Its breeding sites are protected within the Natura 2000 network of the European Union.

Breeding and Migration

Breeding occurs in small, scattered colonies on inaccessible coastal cliffs from February to June. They nest in burrows or rock crevices, laying a single white egg. Both parents share incubation and chick-rearing duties. Post-breeding dispersal begins in June, with most of the population migrating into the Atlantic via the Strait of Gibraltar by July. They return to the Mediterranean in late winter. Migration routes have been studied using geolocator tags, revealing key staging areas in the Gulf of Cádiz and off the coast of Galicia.

Category:Seabirds Category:Birds of Europe Category:Birds of Africa Category:Critically endangered animals Category:Fauna of Spain