Recent changes in allometric relationships among morphological traits in the dipper (Cinclus cinclus)

Organisms are responding to recent climate warming by changing different aspects of their biology, including morphology. The present work examines the way in which dipper (Cinclus cinclus) morphology has varied over the past 20 years (1985-2005) in Sierra Nevada (south-eastern Spain). Tarsus length has decreased, but wing and tail length have increased in the same period. These opposite trends have provoked changes in the allometric relationships among the different parts of the body in the dipper. A decrease in body size is predicted by Bergmann's rule, and similar results have been found in other birds. However, although this study found a decrease in tarsus length, no change was found for body mass. The increase in wing and tail length may be related to a variation in the trophic niche in response to the decrease in water volume of rivers that occurred during the study period. Other studies show that the dipper's diet varies with water flow, and water flow has decreased in the study area as a consequence of climatic warming.