ANDEAN TEMPERATE FOREST OWLS: DETECTABILITY, HABITAT RELATIONSHIPS AND RELIABILITY AS BIODIVERSITY SURROGATES

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South American temperate forests are globally exceptional for their high concentration of endemic species. These forests are among the most endangered ecosystems on Earth because nearly 70% of them have been lost. Current knowledge of most Neotropical forest owls is limited. I studied how environmental and habitat conditions might influence the ecology of sympatric forest owls, and evaluated whether owls can be used as surrogates for temperate forest biodiversity. Specifically, I examined (i) factors associated with the detectability, (ii) occurrence rates and habitat-resource utilization across spatial scales, and (iii) surrogacy reliability of the habitat-specialist rufous-legged owl (Strix rufipes) and the habitat-generalist austral pygmy-owl (Glaucidium nana) in southern Chile. During 20112013, I conducted 1,145 owl surveys, 505 vegetation surveys and 505 avian point-transects across 101 sites comprising a range of conditions from degraded habitat to structurally complex old-growth forest stands. I recorded 292 detections of S. rufipes and 334 detections of G. nana. Detectability for both owls increased with greater moonlight and decreased with environmental noise, and greater wind speed decreased detectability for G. nana. Detection of both species was positively correlated with the detection of the other species. For S. rufipes, occurrence probability ranged from 0.05-1 across sites, and was positively associated with bamboo density and the variability in diameter at breast height of trees (multi-aged forests). For G. nana, occurrence ranged from 0.67-0.98, but no habitat characteristic was related to this species occurrence. Relative to G. nana, S. rufipes had lower total resource utilization, but achieved similar peak occurrence for resources related to stand-level forest complexity and forest homogeneity at the landscape scale. I found that only S. rufipes was a reliable surrogate for all avian biodiversity measures, including endemism and functional diversity. With increasing occurrence of habitat-specialist owls, the density of target specialized biodiversity (guilds and communities) increased nonlinearly and peaked at the least degraded sites. This “specialist aggregation” was driven by forest-stand structural complexity. Forest management practices that maintain multi-aged stands with large trees and high bamboo cover will benefit both owl species, and likely will benefit vulnerable endemic species and specialized avian communities in temperate forests.