Resumen de Modelling the spatial distribution of Tengmalm�s owl Aegolius funereus in its Southwestern Palaeartic limit (NE Spain)
Agustín Castro, Antonio-Román Muñoz, Raimundo Real
Aims: The main objectives of the study are (1) to predict and explain the Tengmalm's owl distribution in peninsular Spain, (2) to generate maps of geographically favourable and unfavourable areas for the species, and (3) to infer the potential trends of the species' range boundaries.
Location: Pyrenean range, peninsular Spain.
Methods: We modelled the spatial distribution of the species using multivariate statistical techniques and GIS (Geographic Information System). To infer the factors affecting the Tengmalm's owl distribution, and to find out favourable areas in Spain, a predictive distribution model was performed using a favourability function, presence/absence data of the species, and a set of 32 independent variables related to climatic conditions, spatial structuring, topography, lithology and human activity. Presence/absence data for the Spanish 10 x 10 km UTM squares were obtained from the Atlas of breeding birds of Spain. Variables included in the model were grouped in factors and we used a variation partitioning procedure to determine how much of the final model variation was explained by the pure effect of each of them in the model and by their interactions.
Results: The resulting model included four variables, namely mean annual number of frost days, maximum precipitation in 24 hours, elevation range, and geographical longitude. Attending to the favourability values yielded, we obtained 107 favourable squares, 4971 unfavourable ones, and 89 classified as of intermediate favourability. Climate was the main factor affecting the Tengmalm's owl distribution, followed by pure spatial structure and topography.
Conclusions: Our global predictive model describes satisfactorily the Tengmalm's owl distribution in Spain with a limited number of climatic, topographical and spatial structuring variables, suggesting that Eastern mountainous territories with many frost days per year and high levels of precipitation recorded in a day are favourable for the species. In Spain, Tengmalm's owl distribution seems to be mainly determined by climatic influence but the influence of spatial structuring may also indicate that Central European area acts as historic source of immigrants. We suggest that the role of French populations as a source population for the Spanish populations may be critical for the maintenance of this endangered species in Spain.
