USGS NSO Studies

The USGS has a page describing 3 studies of the northern spotted owl. Excerpts:

Study #1: Franklin and his colleagues found that northern spotted owl populations have experienced significant yearly declines, translating to a 65-85% population decrease on many of the study areas between 1995 and 2017. Barred owl presence on northern spotted owl territories was the primary factor negatively affecting apparent survival, recruitment, and ultimately, rates of population change. Without removal or reduction of barred owl populations, it’s likely northern spotted owls will become locally extinct from portions of their range. The species would possibly linger on as small populations in other areas until those populations are eliminated by catastrophic events, such as wildfire, resulting in its extinction.

Study #2: Using data collected from 4,118 northern spotted owls in Oregon and Washington from 1990 to 2017, the researchers found the percent of northern spotted owls dispersing from their territories each year has increased by more than 17% in recent times. The increases coincided with a rapid increase in numbers of invasive barred owls as they quickly colonized Pacific Northwest forests and displaced northern spotted owls from their preferred breeding sites.

Study #3: Removal of barred owls had a strong, positive effect on the survival of northern spotted owls, stopping their long-term population declines. After removals, northern spotted owl population declines stabilized in areas with removals but continued to decrease sharply in areas without removals. “The results of the study showed that long-term survival of northern spotted owls will depend heavily on reducing the negative impacts of barred owls while simultaneously addressing other threats such as habitat loss,” added Wiens.

Nothing all that surprising here. I’d like to see a region-wide study of the effects of wildfire on NSO and barred owls. One might surmise that, with millions of acres of post-fire habitat, barred owls will be at a further advantage.


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