Ardea
Official journal of the Netherlands Ornithologists' Union

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Isenmann P. (1976) Contribution a l'etude de la biologie de la reproduction et de l'etho-ecologie du Goeland railleur, Larus genei. ARDEA 64 (1-2): 48-61
A contribution to the breeding biology and the etho-ecology of the Slender-billed Gull Larus genei. This study deals with observations collected during four breeding seasons (1972-1975) in the Camargue (Rhone-delta, France) and a journey to Tunisia (December 1973). The species is present in the Camargue during spring and summer only. Prior to 1971, it bred only irregularly. In 1973, however, there were 12 breeding pairs and in 1975 about 15-20. The breeding cycle lasts from mid-May to the end of July. Breeding pairs are often formed before they arrive on the breeding grounds. Both partners of a pair share the different activities of the breeding cycle. Nesting takes place in colonies on islands in lagoons; these islands are usually covered with sparse vegetation, but are sometimes completely bare. Size of nests and inter-nest distances are presented. The feeding habitat consists of shallow brackish lagoons rich in fish and salt-pans with plankton (Artemia salina). Chicks are fed almost exclusively with fish. Adults have been seen fishing as far as II km from the nesting place. In winter quarters in Tunisia, over 99% of the birds observed feeding were foraging in shallow coastal lagoons. The agonistic and sexual displays are described as well as some aspects of their social life. A striking similarity exists with Larus bulleri stemming partly from convergent adaptation to similar nesting habitats, vulnerable to flooding. The hypothesis of Voous (1962) who thinks that L. genei is probably of sarmatic origin is verified by our description of the habitat. It is concluded that L. genei is a specialist feeder (piscivorous in shallow lagoons and accessorily planktonophagous) compared with L. melanocephalus (Isenmann 1975) and L. ridibundus.


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