Comentaris sobre els desplaçaments erràtics de la població catalana de gavià argentat "(Larus argentatus michahellis)" Authors Enric Carrera i Gallissà Francesc-Xavier Vilagrasa Maria-Roser Nebot Abstract The erratical displacements of the Catalan population of the Herring gull (Larus argentatus michahellis) are analysed and discussed, using country observations and 44 recoveries of the 3,104 pulls ringed in the Medes Islands (Girona) and the Ebre delta (Tarragona) colonies. The seven colonies that constitute this population, which is of about 8. 140 couples, are described. It is exposed that a sizable number of the juveniles (22 % according to our recoveries) travels to the French Atlantic Ocean, between the Spanish Basque Country and the Loire delta, from July to November. The farthest recovery occurs 750 km NW from the birth locality. The rest of the juveniles remains near the breeding colonies, entering in the continent and following rivers over a maximum of 160 km from the coast. These movements show a clear parallelism, in space and time, with those of the French Mediterranean population, which make us consider the Franco-catalan mediterranean population, as an homogeneous dispersions nucleus. Although ringing shows the existence of a native population crearly sedentary, on the other side it hasn't been proved that the juveniles gone to the French Atlantic return to the birth areas. The possible penetration routes to the Atlantic of the Franco-catalan population, Ere discussed, the most apropiated, seems the course of the Aude-Canal du Midi-Garonne, probably also used by other sea species (Gavia sp.). Important post-nuptial concentrations are seen out of the Medes Islands breeding area, which seems to indicate that the Franco-catalan population performs moulting migrations. The invernal bird counts of the French and Catalan-levantine Mediterranean Sea are compared, observing that although both breeding populations are quite similar, the invernal populations are very different. The typology and motivation of these movements are discussed, indicating that they don't always have to be considered as erratic. Downloads Download data is not yet available. Downloads Text complet (Català) Published 2005-05-12 Issue Vol. 47 : 1981 (Secció de Zoologia, 4) Section Articles License The intellectual property of articles belongs to the respective authors.On submitting articles for publication to the journal Butlletí de la Institució Catalana d'Història Natural authors accept the following terms:Authors assign to Institució de la Societat Catalana d’Història Natural (a subsidiary of Institut d’Estudis Catalans) the rights of reproduction, communication to the public and distribution of the articles submitted for publication to Butlletí de la Institució Catalana d'Història Natural.Authors answer to Institució de la Societat Catalana d’Història Natural for the authorship and originality of submitted articles.Authors are responsible for obtaining permission for the reproduction of all graphic material included in articles.Institució de la Societat Catalana d’Història Natural declines all liability for the possible infringement of intellectual property rights by authors.The contents published in the journal, unless otherwise stated in the text or in the graphic material, are subject to a Creative Commons Attribution-NonCommercial-NoDerivs (by-nc-nd) 3.0 Spain licence, the complete text of which may be found at https://creativecommons.org/licenses/by-nc-nd/3.0/es/deed.en. Consequently, the general public is authorised to reproduce, distribute and communicate the work, provided that its authorship and the body publishing it are acknowledged, and that no commercial use and no derivative works are made of it.The journal Butlletí de la Institució Catalana d'Història Natural is not responsible for the ideas and opinions expressed by the authors of the published articles.