Ecología trófica y selección de hábitat del martín pescador Alcedo atthis L.1758 en Navarra

Resumen

The Common kingfisher Alcedo atthis L. 1758 is a fish eating bird which is associated with freshwater bodies in well conserved conditions. Currently, there is a negative trend in their European populations, so it is included in the threatened lists of species. As a piscivorous bird, its conservational may conflict with fish species of commerciall, recreational or conservation interest. To date, the work on the species are scarce and many of its trophic ecological aspects remain unclear. The present PhD is composed of a number of chapters which aims to clarify these issues and to define the most important factors in the selection of habitat. In order to do that, we established a series of partial objectives summarized in the following points: a) determine the relative importance of biotic (food availability) and abiotic (habitat structure and quality) in the presence of the species during breeding (chapter 1); b) develop a useful methodology to determine the diet of the species from partial examination of pellets found in the nests (chapter 2); c) describe the diet and determine, based on the food availability, its fishing strategy (opportunistic or selective) (chapters 3, 4 and 5) and d) determine the impact of the Common kingfisher on both a commercially important fish and conservation species such as the Atlantic salmon (chapter 6). The main conclusions of this PhD dissertation are: 1) food availability is not significant in the breeding territories selection in the rivers of the northern half of Navarra, although they tend to settle in sections with higher concentration of dissolved oxygen, less depth and fewer artificial structures in the river; 2) a review of 130 diagnostic bones is enough to estimate the composition of the diet with a reliability of 95%; 3) species which compound the bulk of the diet belong to the cyprinidae family (94%) with the minnows Phoxinus biguerri Kottelat 2007 being the most consumed species of all; 4) feeding strategy during the breeding period has been revealed as opportunistic, consuming preferably the more accessible prey; 5) although there is a preferred intake range between 50 and 60 mm, there are differences according to both the ecological and biological characteristics of the prey species; 6) there is no selection of prey for feeding chicks, according to a higher energy content and 7) Atlantic salmon intake in the River Frome (southern England) had no significant effect, which accounts for less than 5% of their diet and less than 0.8% of the population of salmon in this river