Balearic shearwaters are one of Europe’s most critically endangered species, with breeding limited to specific locations in Spain’s Balearic Islands in the Mediterranean Sea. International conservation efforts are in place to attempt to reverse a worrying decline in numbers.
Balearic Shearwater in-flight looking for food
Balearic Shearwater flying over the coast
Balearic Shearwater diving into the sea to catch prey
Family:Petrels and shearwaters
34cm to 39cm
83cm to 93cm
472g to 565g
Balearic Shearwaters are medium-sized seabirds with dark grey upperparts and grey-brown underparts. In some birds, buff-white markings are visible on the throat, breast and belly. Balearic shearwaters have ash-grey and white underwings, which are marked with dark diagonal bars. Their bills are dark and their legs and feet are pinkish with dark, scattered markings.
Both sexes look alike, although males are usually fractionally larger in size and weight.
Juvenile Balearic shearwaters are similar in appearance to adults but can be distinguished in their first summer by the darker colour of their fresh, unworn plumage.
Balearic Shearwater in-flight over the open sea
Balearic shearwaters are larger than their close relative the Manx shearwater. Females are marginally smaller and lighter in weight than males, although there may be some overlap between larger females and smaller males.
Balearic Shearwater in-flight over the blue ocean
Balearic shearwaters are silent at sea, and can only be heard calling when at their breeding colonies. Their call is a two-note cry, which is shorter in length in females than males, and can sound like a raucous cackle when heard among other pairs on breeding grounds.
Balearic Shearwater taking-off from the water
Pelagic fish, from open marine waters, form the bulk of a Balearic shearwater’s diet, with anchovies, sprats, and sardines among the most common prey. Squid, molluscs, and crustaceans are also frequently eaten. Prey is located by eye, and caught by plunging into the waves.
Anchovies are the main fish fed to young Balearic shearwaters by their parents for the first 15 days of their life.
Balearic Shearwater diving for fish
Breeding grounds favoured by Balearic shearwaters are found on rocky islets and offshore islands. Coastal landscapes, including isolated cliffs, are sometimes used as nest sites, although burrows, caves, and crevices are preferred. Winters are generally spent offshore, with birds rarely coming inland.
Balearic shearwaters breed exclusively in the Mediterranean’s Balearic Islands, dispersing only temporarily post-breeding to spend the late summer and early autumn along the Atlantic coasts.
Summer sightings are regularly reported in southwestern Europe, including coastal areas of mainland Spain, Portugal, France, the southwestern UK, and parts of northwestern Morocco.
Balearic shearwaters return to the Mediterranean in autumn, and spend winters foraging offshore in the same waters they use when breeding.
Spain’s Balearic Islands, after which the species is named, are the sole breeding grounds of Balearic shearwaters. The majority breed in Mallorca, with colonies there home to an estimated 900 pairs each year, while sizeable colonies are also found at Formentera (712 pairs), Ibiza (650 pairs), Menorca (405 pairs), and Cabrera (475 pairs).
Balearic Shearwater stretching its wings
Up to 2,000 sightings of Balearic shearwaters are reported off the British coastlines each year, although these are limited to the late summer months of July to September. The European population is estimated at around 3,142 pairs, making it one of Europe’s rarest breeding birds.
Balearic shearwaters are regularly seen as passage visitors in the late summer, straying briefly from their northern migrations from breeding grounds to the Bay of Biscay.
Sightings are most common along the southern coast of England, in Dorset, Devon, and Cornwall, as well as on the west coast of Wales. Further north, visiting Balearic shearwaters can also occasionally be spotted along the North Sea coast.
Balearic Shearwater in-flight over the coast
Breeding is possible from 3 years onwards, although 6 years is more common. The average lifespan for Balearic shearwaters is around 12 years, with older individuals recorded occasionally, including one that reached 23 years.
Peregrine falcons are common predators of both adult and young Balearic shearwaters. Introduced predators are a major factor in the declining population of the species, with black and brown rats, feral cats, and common genets the leading threats.
Balearic shearwaters are protected under the Wildlife and Countryside Act, of 1981, which makes it illegal to kill, injure or take them into captivity.
Due to the critically endangered status of the species, conservation action plans for Balearic shearwaters were approved by Spain, in 2005, and France, in 2020. Special Protection Areas have been designated to safeguard the species’ coastal breeding grounds in Spain, Portugal, and France.
Balearic shearwaters are rated as a critically endangered species globally and have Red status on the British Birds of Conservation Concern list. Numbers are declining rapidly and it is feared that up to 90 percent of the current population level could be lost within three generations.
Balearic shearwaters have a relatively small breeding population and significant declines in numbers are reported each year.
Low survival rates are caused by predators attacking breeding colonies (particularly rats, cats, and other introduced predators) and birds becoming trapped at coastal fisheries and dying as by-catch. It’s predicted that unless urgent conservation action is implemented, the species could become extinct in about 60 years’ time.
Balearic Shearwater catching fish
Balearic shearwaters breed in burrows, caves and crevices on rocky islets and remote coastal cliffs. Some sparse plant material may be added.
Nests are usually only visited at night to lower the risk of predation. Colonies are typically fairly small, with loose gatherings of individual nests up to a few hundred pairs nesting in the same area. Balearic shearwaters show strong fidelity to nesting sites and pairs return to the same colonies year after year.
Balearic shearwaters lay their eggs from late February at the earliest, but more usually from early to mid-March. After laying, the female heads off to sea for up to two days, so the initial incubation falls to the male, after which pairs take it in turns.
Incubation is believed to last for around 50 to 52 days, and chicks hatch in late April to early May. Adult Balearic shearwaters depart from their colonies from late June onwards, a few days before chicks are ready to fledge.
Balearic shearwaters lay one white egg, measuring 61 mm by 42 mm (2.4 in by 1.7 in).
Balearic shearwaters form long-term pairs, and return together to breed at the same colonies they have used in previous years. ‘Sabbatical years’ are sometimes reported, when pairs do not breed.
Balearic Shearwater about to take-off from the ocean
Balearic shearwaters are a sociable species, nesting in fairly close proximity to each other and feeding in large groups at sea. Territorial behaviour is not observed, and little time is spent on land.
During the breeding season, Balearic shearwaters are active at night, visiting their burrows after darkness falls to draw as little attention as possible to their nest sites.
Balearic Shearwater resting out at sea
Balearic shearwaters do not migrate in the traditional sense but stray briefly from their breeding grounds once they have raised their young, before returning to spend winters offshore at their usual breeding locations.
They breed only in the Balearic Islands, but post-breeding many head for the Bay of Biscay on the Atlantic Ocean, and are regularly spotted further afield, around the coasts of the North Sea, or into the southern Mediterranean as far south as north-western Morocco.
Occasional summer visitors to UK waters, Balearic shearwaters are not native to the UK and are rarely spotted inland. Sightings are most common between July and September when they return to waters near their breeding grounds to forage offshore during winter months until breeding begins again the following spring.
Balearic Shearwater in-flight over the ocean
Manx shearwaters and Balearic shearwaters are very similar in appearance; however, there are a few subtle differences that make it possible to tell them apart.
Balearic shearwaters are larger than Manx shearwaters, and their plumage is lighter and less contrasting. Their calls are also slightly higher in pitch. Manx shearwaters are far more abundant, with more than 300,000 pairs breeding on coastal islands around the UK.
The breeding population of Balearic shearwaters is officially estimated at 3,142 pairs. With breeding usually not occurring until 6 years, this number is swelled by a large population of non-breeding individuals, giving an overall estimate of between 24,000 and 26,500 birds.
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