First general survey of gulls and terns (Laridae) wintering in the Iberian Peninsula (January 1984)
Published: Volume 33(1-2), June 1986. Pages 47-68.
Original Title: Primer censo general de gaviotas y charranes (Laridae) invernantes en la Península Ibérica (enero de 1984)
The results of this first winter survey of gulls and terns, which was jointly organized by the Iberian Seabird Group, the Spanish ornithological Society, CODA- ICBP Spain, and CEMPA -Secretaria de Estado do Ambiente-, are presented and dicussed in this study. More than 300 observers took part in the fieldwork. The extent of the coverage is tentatively estimated in 70-80 % of the birds actually present (the hinterland was not thoroughly surveyed but the number of birds involved are presumably small). Up to 565.831 birds were censured, 304.414 of which correspond to the Atlantic coast (approximately 2.300 Km of coastline), 212.321 to the Mediterranean coast (1.700 Km. of coastline) and 49.096 to inland areas. The regions most densely populated are Catalonia (23 % of the total), Galicia (19 %), Central Portugal (12,5 %) and Southwestern Andalucia (10.5 %). The most important areas are those of the Rias Bajas in Galicia (about 64.000 birds), the Tagus estuary (62.000), the Guadalquivir Maridmas (16.000), the Albufera of Valencia (26.000), the Ebro Delta (38.000), the Bay of Rosas (39.000), and the suburban areas around Madrid 32.000) and Barcelone (23.000). For the different species a brief review is made on its winter status in the extreme Southwestern Palearctic, by comparing this census with recent surveys carried out in Mediterranean France (ISENMANN, 1980), Italy (FASOLA, 1984), Algeria (JACOB, 1979) and Morocco (BEAUBRUN & THEVENOT, 1984). The Black-headed Gull (Larus ridibundus) is the most abundant species (accounting for 53% of the total numbers of birds). also being the most widely distributed and the only one which is common inland. The Herring Gull Yellow-legged Gull Larus argentatus/ cachinnans), which amounts to 102.160 birds in the Atlantic and 38.882 in the Mediterranean, comes directly afterwards. The number of this species seem to be consistent with recent estimates of the size of the Iberian breeding population (up to 47,7 % of the birds were censused in Galicia). The Lesser Blackbacked Gull (Larusfuscus) enters the Mediterranean (8.879 birds) as far as Barcelone, but remains much more common in the Atlantic (89.907 birds). It is specially abundant in low, sandy coasts, where the Herring Gull becomes scarce, as is the case for a major part of Portugal (26.880 birds in the Tagus estuary) and for Southwestern Andalucia. The importance of the wintering of the Mediterranean Gull (Larus melanocephalus) is worth mentioning: 18.279 were counted, most of them between Castellon and Barcelone, which constitutes the biggest wintering concentration yet recorded in the Mediterranean Sea. The Kittiwake (Rissa tridactyla) numbers were clearly unusual (1.432 birds), this being related with the influx reported for the French, Iberian and Moroccan coasts during January and February of 1984. The other 9 gull species were reported in very low numbers. The observations of Slender-billed Gull (Larus genei), Audouin Gull (L audouinii), Iceland Gull (L. glaucoides) and Glaucous Gull (L. hyperboreus) are of interest since they have been rarely reported in winter in the Iberian Peninsula. The only common tern is the Sandwich Tern (Sterna sandvicensis), with 950 birds in the Atlantic coasts and 434 in the Mediterranean ones (not well surveyed for this species). The other three tern species are scarce. Worth mentionnig is the presence of the Little Tern (St. albifrons): 3 birds in 3 localities.