Managing emerging threats to spotted owls

Abstract

The 3 spotted owl (Strix occidentalis) subspecies in North America (i.e., northern spotted owl [S. o. caurina], California spotted owl [S. o. occidentalis], Mexican spotted owl [S. o. lucida]) have all experienced population declines over the past century due to habitat loss and fragmentation from logging. Now, the emerging influences of climate change, high-severity fire, and barred owl (Strix varia) invasion also appear to be synergistically and differentially affecting population trends of each subspecies. Our objective was to review the existing literature on the spotted owl to describe historical and emerging threats and whether those threats have been adequately examined for each subspecies. Using 527 publications from a Web of Science search of the literature from 1900-2015, we statistically evaluated the emphasis placed on each subspecies regarding 4 influences: mechanical tree removal, fire, climate change, and barred owl invasion. There were 98 papers that explicitly examined the effects of !1 of these influences. Most of these papers were focused on the northern spotted owl, and for all 3 subspecies, most papers examined short-term effects only. We used our results to identify significant information gaps relative to historical and emerging threats. Commercial timber harvesting remains a potential threat for all 3 spotted owl subspecies, but effects from forest thinning may be increasing because of the heightened emphasis on fuels reduction and forest restoration treatments on public lands. Owl response to mechanical tree removal, especially forest thinning, remains understudied. Climate change also may threaten all 3 subspecies. Changes in climate likely affect survival and reproduction of spotted owls and their prey, and alter habitat availability by affecting disturbance regimes and vegetation composition and succession, but little empirical information is available describing specific responses to climate change. The literature on response to high-severity fire is sparse for some subspecies, primarily short-term in nature, and not consistent. Barred owl invasion is a major threat to the northern spotted owl and the California spotted owl but does not currently threaten the Mexican spotted owl. Rigorous research on the response of spotted owls to all factors influencing population change, particularly for the Mexican spotted owl, is needed. The most useful information for predicting owl response to these threats stems primarily from long-term studies of owl demography. The lack of such studies within the range of the Mexican spotted owl greatly limits our understanding of its population dynamics and our ability to predict the effects of various threats on Mexican spotted owl populations. For all 3 subspecies, we encourage long-term studies of their responses to threats, using uniquely marked owls across large spatial extents to account for spatiotemporal variability in ecological conditions within and among subspecies. Ó 2018 The Wildlife Society.

The effect of scale in quantifying fire impacts on species habitats

“…Increases in fire size and severity have led to concerns over the effects of fire in general, and of megafires in particular, on populations and habitats of native wildlife species, including the spotted owl (Strix occidentalis Xántus de Vésey; e.g., Jones et al 2016;Ganey et al 2017;Wan et al 2018b;Wan et al 2019b). There are three recognized subspecies of spotted owls-California (S. occidentalis occidentalis Xántus de Vésey), Mexican (S. occidentalis lucida Nelson), and northern (S. occidentalis caurina Merriam)in North America.…”

Is fire “for the birds”? How two rare species influence fire management across the US

“…Consequently, many managers focus fire-risk reduction activities outside of these areas, leaving occupied nesting sites vulnerable to high-severity fires. As with the CSO, integrating nesting habitat retention with plans to reduce landscape-scale fire risk and restore resilient forests remains one of the greatest challenges facing land managers in the southwestern US (Ganey et al 2017;Wan et al 2018).…”

The influence of different aspects of grouse moorland management on nontarget bird assemblages

“…Biodiversity conservation often produces tension between bodies wishing to maintain species of conservation concern and those that wish to use the areas occupied by species for other purposes (Sillero-Zubiri, Sukumar, & Treves, 2007). Well publicized examples of such conflicts of interest include the reintroduction or recovery of large predators (e.g., gray wolves Canis lupus in Europe and the USA- Mech, 2017), the control of species that limit agricultural productivity (e.g., geese and common crane Grus grus on European farmland-Mason, Keane, Redpath, & Bunnefeld, 2017), and the occurrence of threatened populations in areas of prime real estate development (e.g., the clearance of coastal habitats for development- Drius et al, 2019) or of high extractive use value (e.g., spotted owls Strix occidentalis in old growth forests- Wan, Ganey, Vojta, & Cushman, 2018). Such conflicts of interest can become entrenched into opposing factions, with little opportunity to realize solutions .…”