Do northern spotted owls use harvested areas?

Irwin, Larry L.; Rock, Dennis F.; Rock, Suzanne C.

doi:10.1016/j.foreco.2013.04.001

Cited by 8 publications

(12 citation statements)

References 45 publications

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“…This implies that the probability of use decreased in stands with significantly greater or lesser retained basal area: stands evidently can be too dense or too open, similar to conclusions regarding longer-term effects of partial harvesting in Irwin et al (2012). This and information in Irwin et al (2013) suggests that the most-intensive partial harvests in nesting and roosting habitat were used less frequently. Also, our information suggests that the retained mid-story trees probably facilitated successful acquisition of prey by providing perch sites from which owls hunted and possibly increased foraging efficiency via increased access to prey.…”

Section: Discussionmentioning

confidence: 54%

“…Given information presented herein and previous research (Carey and Peeler, 1995;Fiedler and Cully, 1995;Carey, 2003a,b;Irwin et al, 2004Irwin et al, , 2013Sullivan et al, 2013), we suggest managers consider a modified view in which judicious applications of silvicultural practices, primarily commercial thinning, are likely to improve the values of low-quality foraging habitat for spotted owls in the short run. This would include young and intermediate forests with dense canopy cover but without large trees, multiple canopy layers and canopy gaps that typify nesting and roosting habitat.…”

Section: Management Implicationsmentioning

confidence: 69%

“…If a mapped triangulation polygon was >2 ha, we discarded it and recorded another sample. In previous reports that included many of the radio-tagged owls included herein (e.g., Irwin et al, 2007Irwin et al, , 2013, we noted that the average distance of estimated locations to the true geo-referenced transmitter locations was 84 m (SE = 16 m), with a median value of 56 m, and 94% of the triangulations resulted in error polygons <1.0 ha. We presumed that nocturnal activities primarily involved foraging, although other behaviors such as territorial interactions occur at night.…”

Section: Methodsmentioning

confidence: 81%

“…Similarly, the latest federal recovery plan for the northern spotted owl included options for forest managers to contribute to conservation via thinning (USFWS, 2011). Such active management is supported by additional observations of both the California and northern subspecies of spotted owls nesting or foraging preferentially in forests that were thinned or partially harvested in the past (e.g., Zabel et al, 1992;Buchanan et al, 1995;Lee and Irwin, 2005;Irwin et al, 2007Irwin et al, , 2012, particularly during the non-nesting season (Irwin et al, 2013).…”

Section: Introductionmentioning

confidence: 92%

“…Retaining early-seral dominants such as Douglas-fir and sugar pine (P. lambertiana), including scattered old remnants, should be management goals. More intensive partial harvests such as shelterwood or seed-tree preparatory harvests seem likely to result in negative effects on spotted owls, except in areas known to be used by owls in winter (Irwin et al, 2013).…”

Section: Mixed Conifer Forestsmentioning

confidence: 99%

See 4 more Smart Citations

Forest ecosystem restoration: Initial response of spotted owls to partial harvesting

Irwin

Rock

et al. 2015

Forest Ecology and Management

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Section: Discussionmentioning

confidence: 54%

Section: Management Implicationsmentioning

confidence: 69%

Section: Methodsmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 92%

Section: Mixed Conifer Forestsmentioning

confidence: 99%

See 3 more Smart Citations

Forest ecosystem restoration: Initial response of spotted owls to partial harvesting

Irwin

Rock

et al. 2015

Forest Ecology and Management

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Managing emerging threats to spotted owls

et al. 2018

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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.

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Barred Owl Effects on Spotted Owl Resource Selection: A Meta‐Analysis

Irwin

Rock

et al. 2019

J Wildl Manag

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We quantified the effects of barred owls (Strix varia) on fine‐scale (~2 ha), spatially explicit selection of putative foraging habitat by 175 radio‐tagged northern spotted owls (Strix occidentalis caurina) from 1998 to 2012 in western Oregon and northern California, USA. We constructed annual nighttime discrete‐choice resource selection functions (RSFs) for northern spotted owls in 8 study areas. We compared RSFs from pooled data from 4 study areas where barred owls were absent or rare (≤14% of spotted owl territories potentially influenced by barred owls) with RSFs from 4 study areas where barred owls were abundant (≥89% of spotted owl territories potentially influenced by barred owls), and we conducted a meta‐analysis of all 8 study areas. Top‐ranked RSFs for individual study areas indicated that the relative probability a forest patch was selected by northern spotted owls for foraging was most strongly associated with basal area of large coniferous trees (≥66 cm diameter at breast height [dbh]) or quadratic mean diameter (QMD, the diameter of trees of average basal area) of all coniferous trees. The influence of such trees was non‐linear, usually quadratic, in 7 study areas, suggesting that an optimal basal area of large‐diameter trees or QMD may be associated with selection of foraging patches. The relative probability of selection of such trees decreased nonlinearly with increasing distance from nest sites in ≥4 study areas. Basal area of all or specific hardwood tree species was linearly associated with increases in the relative probability of a patch being used for foraging in 7 of 8 study areas. The relative probability of selection was also positively associated with densities of large snags (>50 cm dbh), coarse woody debris, and undergrowth shrubs in most study areas where we estimated those covariates. The relative probability that a patch was selected decreased nonlinearly with increasing distance from streams (7 study areas), increasing elevation (5 study areas), and decreasing slope (5 study areas). Barred owls exerted strong effects on habitat selection by spotted owls, which may have attempted to minimize interference competition via spatial segregation. Spotted owls occupying study areas where barred owls were abundant used foraging patches at greater distances from streams, at greater distances from nest sites, and on steeper and warmer slopes than those occupying areas with few or no barred owls. In addition, northern spotted owls in areas where barred owls were abundant exhibited reduced selection for large‐diameter trees close to nest sites but may have compensated by increasing use of large trees in home‐range locations distant from nest sites. Programs that seek to improve the link between spotted owl demographic performance or occupancy rate and habitat conditions should account for the influences of fine‐scale variation in vegetation composition and structure and physiographic conditions. Forest managers may contribute to spotted owl conservation via silvicultural prescriptions ...

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Do northern spotted owls use harvested areas?

Cited by 8 publications

References 45 publications

Forest ecosystem restoration: Initial response of spotted owls to partial harvesting

Forest ecosystem restoration: Initial response of spotted owls to partial harvesting

Managing emerging threats to spotted owls

Barred Owl Effects on Spotted Owl Resource Selection: A Meta‐Analysis

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