Balearic Shearwaters

from Wikipedia, the free encyclopedia
Balearic Shearwaters
Swimming Balearic Shearwater

Swimming Balearic Shearwater

Systematics
Class : Birds (aves)
Order : Tubular noses (Procellariiformes)
Family : Petrels (Procellariidae)
Genre : Puffinus
Type : Balearic Shearwaters
Scientific name
Puffinus mauretanicus
Lowe , 1921
View of the top in flight
Wing underside in flight
The Balearic Shearwater breeds on the cliffs of the Balearic Islands, such as the Mallorcan island of Sa Dragonera
Location and population size (in breeding pairs) of the known colonies of the Balearic Shearwater in 2009
Seasonal distribution and schematic migratory movements of the Balearic Shearwaters: orange - main feeding waters during the breeding season, streaky orange - entire action area during the breeding season, blue - oversummer in larger numbers, striped blue - entire action area in summer, solid lines - main migratory routes, dashed lines - migratory movements in very small numbers

The Balearic Shearwater ( Puffinus mauretanicus ) is a species of bird from the family of the Petrels (Procellariidae), the only on the Balearic Islands breeds. Because of the small, assumed population of at times less than 2000 breeding pairs, the species is classified by the IUCN as "critically endangered". After the breeding season, the birds migrate through the Strait of Gibraltar to spend the time of the winged moult in the Western European Atlantic, especially in the Bay of Biscay . They then return to the western Mediterranean to hibernate. The species breeds in caves on cliffs and on offshore islands. It feeds mainly on small schooling fish.

In the past, the Balearic Shearwater was considered a subspecies of the Mediterranean Shearwater . Since it is on average somewhat larger and differs significantly in various plumage characteristics, but also in behavior, it has been granted species status for some time. This is supported by genetic and paleontological findings, among other things.

description

With a body length of 30 to 40 cm, the Balearic Shearwater is one of the medium-sized shearwaters and is slightly smaller than a black-headed gull . The wingspan is between 76 and 93 cm. The sexes differ only slightly in size and weight. The weight of the males is between 490 and 565 g, that of the females between 472 and 550 g. In flight, the Balearic Shearwater looks a bit "bulbous". The short tail is surmounted by the toes.

The species is similar to the Mediterranean shearwater, but is about 15% larger; some birds of both species cannot be clearly identified in the field. The upper side is grayish brown, the underside whitish with a variable gray-brownish tint, which is strongly condensed from the lower abdomen to the under tail-coverts. The transition between the top and bottom is washed out on the neck and flanks and not clearly delimited as in the Mediterranean shearwater - the flanks are never pure white. Sometimes the white of the underside is even limited to the middle of the chest and abdomen. The center of the lower wing is tinted rather diffuse ash gray to off-white and not as contrasting white as in the Mediterranean shearwater. There is a faded, brownish bandage in the armpit. The latter appears dark overall in flight.

Young birds in their youthful plumage are similar to adults, but can be distinguished between June and September by their fresh upper side plumage, as older birds moult clearly at this time.

voice

At night in the breeding colonies, the hoarse and falsetto-like screaming and cackling typical of shearwater can be heard. In contrast to the Mediterranean and Atlantic shearwater, the species sounds a bit rougher and deeper.

Distribution and existence

The brood distribution is limited to the Balearic Islands . In 2009, a survey in the colonies showed a total of 3193 breeding pairs. Of these, 900 bred on Mallorca , 747 on Ibiza , 692 on Formentera , 449 on Cabrera and 405 on Menorca . Since the species occurs in Menorca together with the Mediterranean shearwater and many birds cannot be clearly identified, the exact population there is not very easy to determine. In general, counts in colonies are probably unreliable, since a considerable proportion of the birds can evidently be non-breeders.

The IUCN classifies the species as "critically endangered" and is one of the most endangered marine birds in the world. On Cabrera the colonies have declined by 60% in the last decades, on Formentera the population decreased continuously from 1500 birds in the early 1990s to 692 pairs between 2003 and 2006. On the basis of these numbers, an average decrease of 7, 4% calculated, which would lead to extinction of the species in about 40 years. In addition to the low population numbers and limited distribution, the high mortality rate among adult birds is particularly worrying. Sources of threat include predation pressures from bottom predators in the colonies, environmental pollution and the possible danger to birds of being caught as fishermen . In the longer term, the declining fish stocks could pose a threat. However, a risk of hybridization with the Mediterranean shearwater could be excluded by population genetic studies. Likewise, despite the high degree of breeding site loyalty between the colonies, there is apparently sufficient exchange to ensure genetic diversity within the species. The sharp decline has so far not had any genetic impact.

In the traditional moulting roosts in the central Biscay, there were occasional worrying declines: While 8000-10,000 birds were counted there in the 1980s, there were fewer than 2000 at the turn of the millennium. Recent research has shown that this is the case meanwhile large numbers of Balearic shearwaters can be found in the area of ​​the coasts off northern France and the south-western British Isles. Some of the deposits now extend to southern Scandinavia. The local declines therefore do not reflect actual population developments, but are part of a trend in which the whereabouts of the birds have shifted ever further north due to the changing climatic conditions.

In 2015 it was published that according to annual censuses between 2007 and 2010 between 23,780 and 26,535 Balearic shearwaters passed the Strait of Gibraltar after the breeding season. This number far exceeds previous estimates of the total population of 10,000 to 15,000 birds.

hikes

The Balearic Petrel shows a rather unusual migratory behavior. A large part of the population leaves the Mediterranean area through the Strait of Gibraltar in June after the breeding season (non-breeding season as early as May) in order to seek nutrient-rich waters in the western European Atlantic and to summer there. The species is then often found in the coastal area from the Gulf of Cádiz to Galicia . The overwhelming number, however, collects at the swinging moult in the central Biscay and further north to Brittany. The Balearic Shearwater can also be found south of England in mostly smaller numbers, reaching the Irish Sea and the North Sea, as far as Scotland and southern Scandinavia and, exceptionally, the Baltic States. He has been proven to be a random visitor in Germany and Poland.

Since the turn of the millennium, the summer areas seem to have shifted further north due to the increasing warming of the sea surface. The number of annual sightings south of England in the 1980s and 1990s was between 250 and 800, while in 2001 it increased significantly to 3,500. Nevertheless, the focus is apparently still in the Bay of Biscay.

Smaller movements also take place south in the Atlantic. A small part of the coast is covered in summer on North African coasts. Some birds also rarely make it to Cape Verde or Senegambia . Exceptionally, the species was also found in South Africa.

The majority of the population returns to the breeding areas from autumn (September to November) and collects in the winter in the area of ​​the Iberian coasts. Few birds remain in the Atlantic even in winter. In the winter of 2007/2008 around 700 birds overwintered off Brittany and only disappeared in March. This currently unique event must also be seen in connection with a shift to the north.

Small parts of the population are resident birds , which spend the whole year in the breeding area or on the coast of eastern Spain.

habitat

The Balearic Shearwater is a sea ​​bird , which, however, mainly hangs out in coastal waters or in the area of ​​the shelf to forage. It breeds in caves on the rocky coasts of the main Balearic Islands or on small islets offshore.

nutrition

The Balearic Shearwater feeds mainly on small schooling fish such as anchovies , species of mackerel ( Scomber sp.), The sand smelt Atherina mochan , sprats or sardines and occasionally on small squids and crustaceans such as the luminous shrimp . It catches its prey mainly by submerging briefly or in small dives of usually 5–6 m depth, but can also dive up to 26 m deep and for over a minute. Often larger groups gather in search of food and sometimes the kind of fishing boats follows. The activity peaks in foraging are in the early morning hours, early afternoon and at sunset. A nocturnal foraging for food has not yet been confirmed.

Reproduction

The Balaric Shearwater breeds individually or in small colonies, which usually do not exceed a number of 100 breeding pairs. The birds breed for the first time in their third year of life and apparently lead a permanent monogamous marriage. The pairs show a high degree of loyalty to the breeding site. The colonies will be visited from the end of September. From January, the females in particular leave the colony for another five to 22 days before laying their eggs. The eggs are laid between February and April and are very synchronous within the colonies. Most of the young birds fly out in June.

The happening at the hatchery takes place exclusively at night. Due to the threat posed by enemies living on the ground, the nesting sites are often well above sea level and sometimes up to 150 m high. The species nests in caves in the ground, crevices or projections in caves that are poorly lined with plant material. The clutch consists of a single white egg measuring 61 × 42.5 mm and incubated between 50 and 52 days. During the incubation, the partners take turns after a few days. The brooding partner remains on the nest without food, while the other embarks on longer foraging flights. These last at least two days. How far away the birds are is hardly known, but birds from Ibiza are not only to be found in the area of ​​the Iberian continental shelf , but can even be found on the North African coast between northeast Morocco and western Algeria, especially towards the end of the breeding season. Field studies have shown that about 13.5% of the breeding attempts involved additional helpers, seven of which were males and two were females. The nestling period is 72 days.

The breeding success in two colonies on Mallorca was fairly constant at 62%. Peregrine falcons are natural predators to which both young and adult birds fall prey .

Systematics

The Balearic petrel was regarded as a subspecies of the " black-billed shearwater " ( Puffinus puffinus ) until the 1980s, although up to eight subspecies are now all treated as separate species. In the case of the three Palearctic Taxa puffinus , yelkouan and mauretanicus , the populations breeding in the Mediterranean began to split off as “Mediterranean shearwaters” from 1988 onwards. The Balearic Shearwater was treated as a subspecies Puffinus yelkouan mauretanicus . From the beginning of the 1990s, however, morphological, paleontological , genetic, ecological and ethological findings consolidated the view that this subspecies also deserved species status. This was initially widely recognized, but was questioned in 2006 because there are birds in Menorca that are phenotypically and genetically between mauretanicus and yelkouan and indicate a hybridization between the two taxa. However, a 2007 study found that introgression is marginal and is believed to be due to secondary contact between the two species several generations ago. In 2014, the Handbook of the Birds of the World primarily evaluated the morphological distinguishing features as clear arguments for the species status.

literature

  • Josep del Hoyo , Nigel Collar, Guy M. Kirwan : Balearic Shearwater (Puffinus mauretanicus) . In: J. del Hoyo, A. Elliott, J. Sargatal, AD Christie, E. de Juana (Eds.): Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona 2014.
  • Urs N. Glutz von Blotzheim , KM Bauer : Handbook of the birds of Central Europe. Volume 1: Gaviiformes - Phoenicopteriformes. AULA-Verlag, Wiesbaden 1993/2001 (first edition 1966), ISBN 3-923527-00-4 , p. 201 f.
  • Daniel Oro, Juan Salvador Aguilar, José Manuel Iguala, Maite Louzao: Modeling demography and extinction risk in the endangered Balearic shearwater , Biological Conservation 116, 2004, pp. 93-102, doi : 10.1016 / S0006-3207 (03) 00180-0 ( PDF )
  • Meritxell Genovart, Daniel Oro, Javier Juste, Giorgio Bertolle: What genetics tell us about the conservation of the critically endangered Balearic Shearwater? , Biological Conservation 137, 2007, pp. 283–293, doi : 10.1016 / j.biocon.2007.02.016 , ( PDF )
  • José Manuel Arcos (ed.): International species action plan for the Balearic shearwater, Puffinus mauretanicus , SEO / BirdLife & BirdLife International, 2011, ( PDF )
  • Russell B. Wynn, Pierre Yésou: The changing status of Balearic Shearwater in northwest European waters , British Birds 100, 2007, pp. 392–406, ( PDF )

Individual evidence

  1. ↑ Audio sample of a Balearic Shearwater at www.xeno-canto.org
  2. ↑ a b Del Hoyo et al. (2014), Section Status and Conservation , see literature
  3. ↑ a b Oro et al. (2004), see literature
  4. ↑ JM Arcos (2011), p. 13 f, see literature
  5. ↑ Genovart et al. (2007), see literature
  6. ↑ Wynn / Yésou (2007), see literature
  7. ↑ Eduardo de Juana: Migrant counts boost Balearic Shearwater population estimates , Handbook of the Birds of the World Alive, January 27, 2015
  8. ↑ a b c J. M. Arcos (2011), p. 8 f, see literature
  9. ↑ a b c d e Del Hoyo et al. (2014), Migration section , see literature
  10. ↑ a b J. M. Arcos (2011), p. 9, see literature
  11. ↑ a b c J. M. Arcos (2011), p. 7, see literature
  12. ↑ Glutz von Blotzheim, p. 201, see literature
  13. ↑ Genovart et al. (2007), see literature
  14. ↑ Del Hoyo et al. (2014), section Taxonomy , see literature

Web links

Commons : Balearic Shearwater  - Collection of images, videos and audio files