Trophic interactions mediate the response of predator populations to habitat change

Stable isotopes reveal unexpected relationships between fire history and the diet of Spotted Owls

“…Although we could not directly attribute our results to any single mechanism discussed above, our research has important implications for owl ecology and conservation. Using identical isotopic methods, Hobart et al (2019) found that increased proportional consumption of Flying Squirrels was associated with negative consequences for Spotted Owls and that owls relied relatively less on Flying Squirrels in national parks (where fire regimes are restored) than in national forests (where fires are suppressed). Hobart et al (2019) thus speculate that restored fire regimes in national parks may increase the consumption of Woodrats and Pocket Gophers by owls, leading to fitness and demographic benefits.…”

“…Using identical isotopic methods, Hobart et al (2019) found that increased proportional consumption of Flying Squirrels was associated with negative consequences for Spotted Owls and that owls relied relatively less on Flying Squirrels in national parks (where fire regimes are restored) than in national forests (where fires are suppressed). Hobart et al (2019) thus speculate that restored fire regimes in national parks may increase the consumption of Woodrats and Pocket Gophers by owls, leading to fitness and demographic benefits. Indeed, restored fire regimes are a defining ecological characteristic of the national parks studied here (Table S4) – where Spotted Owl populations are stable (Sequoia–Kings NP), are relatively high‐density (Yosemite NP) and are not adversely affected by most fires (Roberts et al 2011, Tempel et al 2017).…”

“…Jones et al 2016) and diet‐based (e.g. Hobart et al 2019) research. Within owl territories (either KDE polygons or circular buffers), we quantified fire history based on two data sources over four overlapping time steps: 5‐year (2012–16), 10‐year (2007–16), 20‐year (1997–2016) and 33‐year steps (1984–2016; see Table S1 for a summarized description of each variable).…”

“…Thus, we predicted that greater prevalence, area and diversity of fire within Spotted Owl territories would act to shift owl diet towards Woodrats and Pocket Gophers and away from Flying Squirrels. Given that the relative consumption of these prey groups may be an important driver of Spotted Owl population status (Hobart et al 2019), improving our understanding of how fire affects diet may offer insights into how changing fire regimes could affect Spotted Owl populations and conservation efforts.…”

Spotted owls and forest fire: Comment

“…Lee (2018:19) states that “forest fire does not appear to be a serious threat to owl populations and likely imparts more benefits than costs for Spotted Owls…” In support of this conclusion, Lee (2018) cites studies suggesting that mixed‐severity fire typically affects “a very small portion (0.02–0.50%) of spotted owl nesting and roosting habitat per year...” We agree that severe fire has not yet resulted in substantial declines in spotted owl populations at regional or subspecies scales and rather that recent declines (Conner et al 2016, Dugger et al 2016, Tempel et al 2016) have occurred for other reasons including competition with barred owls (Diller et al 2016, Dugger et al 2016, Mangan et al 2019), potentially the loss of large trees and old‐forest habitat (Jones et al 2018), and potentially shifts in prey communities (Hobart et al 2019). Certainly, severe fire has caused declines in spotted owl abundance at more local scales (e.g., 100s of km 2 ; Jones et al 2016) and resulted in an enduring loss of nesting and roosting habitat, but fire has not been an overriding driver of recently observed long‐term spotted owl population declines.…”