The Siberian jay Perisoreus infaustus has experienced a large decline due to logging in Finland. Populations may also be at risk due to climate warming and interactions with expanding populations of other corvid species. We assessed causes of Siberian jay population changes in southern Norway by conducting field surveys and an online survey addressed to birdwatchers. Field surveys indicated that density of Siberian jays was related to old-growth forest. Density was lower at sites close to the edge of the southeastern distribution margin. Unexpectedly, presence was positively associated with presence of other corvid species. The online survey indicated decreasing populations in logged areas close to the southeastern distribution margin. Respondents reported an increase of other corvid species, but increases were not correlated with decreases of Siberian jays. The field survey and the online survey did not indicate lower population density or population declines at lower-altitude sites (expected if climate change affected the species) when also taking distance from the edge of the southeastern distribution margin into account. In conclusion, there was a decrease in Siberian jay populations at the southeastern distribution margin related to logging, but other corvid species did not affect population trends. Climate change did not appear to be the main factor causing the decline of the Siberian jay, but it cannot be ruled out.