Recent global warming and other anthropogenic changes have caused well-documented range shifts and population declines in many species over a large spatial extent. Most large-scale studies focus on birds, large mammals, and threatened species, whereas large scale population trends of small to medium-sized mammals and species that are currently of least concern remain poorly studied. Large-scale studies are needed, because on smaller scales important patterns may be masked by local variation and stochastic processes. Here, we utilized snow track census data from Finland and NW Russia to estimate population growth rates of the Eurasian red squirrel (Sciurus vulgaris L) during 17 years in an area of over 1 000 000 km2. We also studied the effects of summer and winter temperature change and loss of canopy cover on estimated red squirrel population growth rates. Our results suggest that red squirrel populations have declined in most parts of the study area, the only remarkable exception being SW Russia. These results are in concordance with previous studies suggesting that still common and least concern species may be declining, but is in contrast to the common pattern of northern populations of boreal species increasing under global warming. The estimated population growth rates are in synchrony over vast areas, suggesting also that the underlying reasons operate on a large scale. However, we find no evidence that the decline is caused by loss of canopy cover or changes in summer temperature, which was used as a proxy for the level of cone crop.