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UBC Theses and Dissertations

Andean temperate forest owls : detectability, habitat relationships and reliability as biodiversity surrogates Ibarra, Eliessetch José Tomás


South American temperate forests are globally exceptional for their high concentration of endemic species. These ecosystems are one of the most endangered biomes on Earth because nearly 60% of forests have been lost. Current knowledge of most Neotropical forest owls is limited. I examined (i) detectability, (ii) occurrence and habitat-resource utilization across spatial scales, and (iii) surrogacy reliability of the threatened habitat-specialist rufous-legged owls (Strix rufipes) and habitat-generalist austral pygmy-owls (Glaucidium nana) in southern Chile. During 2011-2013, I conducted 1,145 owl broadcast surveys, and established 505 vegetation plots and 505 avian point-transects across 101 sites comprising a range of conditions from highly 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 for G. nana greater wind speed decreased detectability. Detection of either 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 the parameter estimates for covariates overlapped zero, meaning they occurred across the full range of habitat conditions. 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 S. rufipes were reliable surrogates for avian species richness, endemism and measures of functional biodiversity (e.g. large-tree users, understorey users, degree of community specialization). Strix rufipes and specialist avian species and guilds aggregated at the relatively stable, 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 owls, and will be linked to a higher density of vulnerable endemic species, specialized wildlife communities and, likely, ecosystem stability in temperate forests.

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