Across the Sierra Nevada, fire suppression and logging have densified and homogenized forests. In response, fuels treatments are being implemented to improve forest resilience to increasingly severe fire and drought. However, the implementation of these treatments is constrained by costs, access, and concern for their effects on wildlife. We compared the effects of severe fire, drought-induced tree mortality, and fuel treatments on the occupancy of the California spotted owl (CSO). We integrated CSO data from a regional acoustic monitoring project and a 15-year disturbance and management dataset to compare disturbance and management at both site- and population levels. CSO occupancy was negatively related to severe fire and positively related to drought-induced tree mortality. When considering treatments in isolation, heavier treatments (mean proportion of site treated (MPST) = 1.1%) had a negative relationship with CSO occupancy, while lighter treatments (MPST = 12.8%) had a positive relationship. However, when controlling for drought and fire, there was no significant effect of either treatment intensity on CSO site occupancy. This is the first study to compare the effects of the primary agents of forest change in the Sierra Nevada on an at-risk species and underscores the need for effective implementation of fuels management.

Osprey and Bald Eagle populations suffered long-term decline and range contraction in California from persecution, habitat loss, and pesticides. Both species are believed to have recovered, but recent changes in geographic range, populations, reproductive success, and habitat use remain mostly unstudied. We studied both species within the central portion of the Central Valley and Sierra foothills. Osprey colonization began in the 1970s, and during 2020-2024, the nesting population increased at only 4.3% annually, suggesting near habitat saturation. Over recent years, 73% of 181 Osprey nest attempts were successful, producing an average of 1.32 young per occupied nest, indicating a healthy population. Osprey nests were mostly placed on artificial structures (91%), mainly utility poles (58%). Over 2011-2024, breeding Bald Eagles increased by 18% annually, from 4 to 31 pairs. Reproductive success was healthy, with 79% of 133 nests successful and 1.29 young fledged per occupied nest. Eagles mostly nested in gray pines, Fremont cottonwoods, and other species near major waterbodies. These two species’ increases have likely resulted from reduced persecution, reservoir construction, nest protection, and contaminant declines. Competition from the increasing Bald Eagle population may reduce Osprey numbers, but habitat selection differences will likely maintain healthy populations of both species.

Environmental disturbances, such as wildfire, drought, and fuel management, are reshaping wildlife habitats in western forests and threatening forest-dependent species like the spotted owl (Strix occidentalis). Here, we used 35 years (1987–2022) of spotted owl detections across the southernmost extent of their geographic range in Southern California to model owl nesting and prey acquisition habitats and evaluate the effects of wildfire, drought, and fuel treatments. We found a 54% decline in nesting habitat and a 40% decline in prey acquisition habitat. Notably, 91% of suitable nesting habitat across years occurred within the San Bernardino Mountains. Wildfires were the main driver of nesting habitat loss, responsible for approximately 30% of the decline, with most large, severe fires occurring after 2003. In contrast, fuel management contributed to only 4% of the loss. The number of potential territories containing sufficient nesting habitat (48 ha) declined by 53%, whereas territories containing sufficient prey acquisition habitat (48 ha) declined by 47%. The number of potential territories with sufficient nesting and prey acquisition habitat decreased by 73%. Our research demonstrates the pronounced impact of wildfires on spotted owl habitat, particularly in the San Bernardino National Forest, while emphasizing the minor negative effect of fuel management.

Golden eagles (Aquila chrysaetos) are one of the largest raptors in North America. They require small mammal populations and consistent nesting substrates. They are a fully protected species in California and a species conservation interest at the continental level. Recent studies provide some understanding of survey methods and eagle density in California. But little is known about population fluctuations, demographics and, gaps exist in knowledge about nesting territory preferences and sizes. To understand eagle demographics, population, nesting and foraging preferences, I conducted eagle surveys during the breeding season on three routes (2019-2024) and baited seven stations with wild pig carcasses (2022-2024). I observed three nesting territories, 14 individual eagles and 9 immature eagles utilized 14,000 acres of central Coast Range blue oak woodland and serpentine grassland. Most eagle foraging was observed in open grasslands of 2,000 acres or more. Nesting occurred in large oak trees on steep slopes – except one nest in a Valley oak tree in a deep canyon. Young eagles dominate the population after breeding season and compete for carrion at carcasses. The population of six breeding adults and 8-10 immature eagles appears to be relatively stable, but environmental factors such as drought and cold/snow limited nesting.

Wildfire has been a fundamental component of natural ecosystem dynamics for millennia. However, climate change and land use have altered fire regimes globally such that that many wildlife species are now threatened by larger, more severe, and/or more frequent wildfires. Fuels reduction treatments may be used to create landscapes that are more resilient to wildfire and lessen the impact of high-severity fire to wildlife. However, there is lingering uncertainty regarding the extent to which fire-adapted species are truly threatened by novel wildfire characteristics. The spotted owl (Strix occidentalis) has become a focal point of controversy owing to its use of forests that have been substantially impacted changing fire regimes. Here, we leveraged over three decades of surveys across 1514 historical spotted owl territories and GPS movement data from 169 individuals across seven national forests, three national parks, and privately owned land in California, USA, to answer the question: “How have spotted owls responded to changing fire regimes?”. Across the region, we found that spotted owl territories were more likely to become vacant and less likely to be colonized if they experienced recent extensive high-severity fire. Movement analysis showed that individual spotted owls were unlikely to select forest burned at high-severity. Thus, our expansive data synthesis provided an unambiguous conclusion to lingering uncertainty: Large and severe fires threaten the persistence of spotted owls across their range. If managers are charged with conserving this species in California, forest restoration and fuels reduction treatments that reduce the risk of large and severe fires without substantial degradation of suitable habitat appear to be necessary.

Abstract: Great gray owls (GGOWs) in the Sierra Nevada are considered a genetically unique subspecies (Strix nebulosa yosemitensis), with low genetic diversity and a small population size. The majority of this population resides in Yosemite National Park where it’s associated with meadow areas subject to short-term disturbances from park activities and is at risk of wildlife-vehicle collisions, the greatest known source of mortality. From March 2022 to March 2024, we collected movement data from five owls with GPS transmitters, and compiled habitat data at use points derived from remotely-sensed data and field-based surveys. We addressed three objectives: (1) describe diel activity and seasonal space use of GGOWs, (2) identify key habitat variables that predict foraging and roosting habitat selection, and (3) determine drivers of habitat selection along roads. We found that GGOW foraging was positively associated with canopy density but negatively associated with number of canopy layers and canopy cover. We also found that GGOW roosting was positively associated with number of canopy layers, canopy density, and canopy cover. This work will aid in the conservation of California’s GGOW population by informing meadow restoration and management of roadside vegetation within GGOW home ranges.