Coexistence of ecologically similar species can be maintained by partitioning along one or more niche axes. Three-dimensional structural complexity is central to facilitating resource partitioning between many forest species, but is underrepresented in field-based studies. We examined resource selection by sympatric northern spotted owls (Strix occidentalis caurina), a threatened species under the US Endangered Species Act, and nonnative barred owls (S. varia) in western Oregon, USA to explore the relative importance of canopy heterogeneity, vertical complexity of forest, and abiotic features to resource selection and identify potential differences that may facilitate long-term coexistence. We predicted that within home range selection of understory densities, measured with airborne lidar, would differ between species based on proportional differences in arboreal and terrestrial prey taken by each owl species. We used discrete choice models and telemetry data from 41 spotted owls and 38 barred owls monitored during 2007–2009 and 2012–2015. Our results suggested that while both species used tall canopy areas more often than low canopy areas, spotted owls were more commonly found in areas with lower tree cover, more developed understory, and steeper slopes. This is the first evidence of fine-scale partitioning based on structural forest properties by northern spotted owls and barred owls.
Long-term conservation planning for diadromous fishes would benefit from a better understanding of both the role of connectivity among environments and habitat variability in the expression of life-history diversity. Most of the scientific knowledge on habitat fragmentation and connectivity has been developed in terrestrial systems in the discipline of landscape ecology. Research on habitat connectivity in aquatic systems (e.g., salmonid research that spans the spectrum of habitats from freshwater to the sea) is uncommon and largely focused on barriers to fish passage. Here, we present a review of the literature characterizing current research patterns on habitat connectivity within and among environments for Pacific salmon. We found this topic is still incipient: the literature is dominated by studies of freshwaters, with few articles focusing on habitat needs in estuary and marine systems. Pan-environment studies are rare, pointing to a gap in our understanding of complex habitat relationships that might be significant in the development of long-term conservation and restoration plans for Pacific salmon, particularly in light of the potential impact of climate change.
The Pacific marten once ranged throughout coastal forests of the Pacific Northwest, but by the late 1940s, it was thought to be extinct. In 1996, however, a population was found in northern California. This member of the mustelid family, which includes weasels and fishers, depends on diverse, mixed-conifer forests with a dense understory of salal and other shrubs. Habitat loss, forest fragmentation, disease, trapping, and fatality from collisions with motor vehicles have contributed to the decline of the Humboldt marten, a subspecies found in limited areas of coastal Oregon.
Conservation efforts have been hampered by a lack of information on distribution, population size, habits, and habitat needs of the Humboldt marten. In the past 4 years, extensive research by scientists with the USDA Forest Service Pacific Northwest Research Station and partners has greatly increased basic understanding of the Humboldt marten, giving resource managers and policymakers new information on which to base decisions.
Using a novel combination of survey techniques, scientists collected data about Pacific marten in Oregon and California, conducting the largest carnivore survey in Oregon. Their findings confirm that small populations of Humboldt martens persist but not only in late-successional forests as previously thought. On Oregon’s central coast, scientists projected that just two to three mortalities a year could lead to extinction of small local populations within 30 years.
Studies of habitat selection and use by wildlife, especially large herbivores, are foundational for understanding their ecology and management, especially if predictors of use represent habitat requirements that can be related to demography or fitness. Many ungulate species serve societal needs as game animals or subsistence foods, and also can affect native vegetation and agricultural crops because of their large body size, diet choices, and widespread distributions. Understanding nutritional resources and habitat use of large herbivores like elk (Cervus canadensis) can benefit their management across different land ownerships and management regimes. Distributions of elk in much of the western United States have shifted from public to private lands, leading to reduced hunting and viewing opportunities on the former and increased crop damage and other undesired effects on the latter. These shifts may be caused by increasing human disturbance (e.g., roads and traffic) and declines of early-seral vegetation, which provides abundant forage for elk and other wildlife on public lands. Managers can benefit from tools that predict how nutritional resources, other environmental characteristics, elk productivity and performance, and elk distributions respond to management actions. We present a large-scale effort to develop regional elk nutrition and habitat-use models for summer ranges spanning 11 million ha in western Oregon and Washington, USA (hereafter Westside). We chose summer because nutritional limitations on elk condition (e.g., body fat levels) and reproduction in this season are evident across much of the western United States. Our overarching hypothesis was that elk habitat use during summer is driven by a suite of interacting covariates related to energy balance: acquisition (e.g., nutritional resources, juxtaposition of cover and foraging areas), and loss (e.g., proximity to open roads, topography). We predicted that female elk consistently select areas of higher summer nutrition, resulting in better animal performance in more nutritionally rich landscapes. We also predicted that factors of human disturbance, vegetation, and topography would affect elk use of landscapes and available nutrition during summer, and specifically predicted that elk would avoid open roads and areas far from cover-forage edges because of their preference for foraging sites with secure patches of cover nearby. Our work had 2 primary objectives: 1) to develop and evaluate a nutrition model that estimates regional nutritional conditions for elk on summer ranges, using predictors that reflect elk nutritional ecology; and 2) to develop a summer habitat-use model that integrates the nutrition model predictions with other covariates to estimate relative probability of use by elk, accounting for ecological processes that drive use. To meet our objectives, we used 25 previously collected data sets on elk nutrition, performance, and distributions from 12 study areas. We demonstrated the management utility of our regional-scale models via application in 2 landscapes in Washington.