Long-term trends in food habits of a relict brown bear population in northern Spain: the influence of climate and local factors

Abstract

Relict endangered populations may be especially vulnerable to the effects of climate change. A data series for the period 1974–2003 was used to examine shifts in brown bear Ursus arctos food habits in its south-westernmost European population. This focused on the hyperphagic season, when bears gain the fat that is essential for winter dormancy and reproduction. General climatic indicators were predictors of diet trends. Other variables potentially able to modify brown bear food habits at the local scale were accounted for by considering two areas where local conditions changed in different ways during the study period. General climatic indicators such as temperature and the winter North Atlantic Oscillation index were good predictors of some diet trends, although local factors seemed to modulate the potential response of food habits to recent climate change. Boreal and temperate food items decreasingly contributed to brown bear diet, replaced by increasing contributions of southern foods, which suggested that warmer temperatures might determine the occurrence of some food items in the diet of Cantabrian brown bears through effects on plant distribution and phenology. At the local scale, high cattle density in one of the study areas limited food sources available for brown bears. Important food sources for brown bears, such as heath-like Vaccinium formations and old-growth oak forest in the Cantabrian Mountains, require increased levels of protection.