Outside Influences

Loss and fragmentation of old-growth forest habitat on a landscape scale
Loss of the majority of low elevation old-growth forest habitat to development and other uses such as timber production was likely the primary cause of the original spotted owl population declines in Washington. Remaining old-growth was often fragmented into small patches that then become unsuitable for spotted owls, because the owls require large continuous patches of old-growth for nesting.

Competition with barred owls.
Spotted owl numbers continued to decline in Washington even after old-growth forest habitat on federal lands was protected in the early 1990s. Most experts believe that the recent increase in barred owls in Washington is the main cause of these continued spotted owl population declines. Barred owls are much more aggressive than spotted owls, and seem to be displacing them from the small refuges of old-growth habitat that remain.

Regional spotted owl population trends.
Because spotted owl numbers are continuing to decline throughout Washington, there are few source populations that can supply dispersing owls. This means that it is becoming less likely that existing old-growth forest habitat in the watershed will be colonized and used for nesting in the future.