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Spotted Owl - Strix occidentalis
Spotted Owl - Strix occidentalis

[Image: 324px-Northern_Spotted_Owl.USFWS.jpg]

Scientific classification 
Kingdom: Animalia 
Phylum: Chordata 
Class: Aves
Order: Strigiformes 
Family: Strigidae 
Genus: Strix 
Species: Strix occidentalis

The Spotted Owl was reported in 1860 by an Hungarian immigrant John Xántus de Vesey. The Latin word "occidentalis" refers to something from the west. Other names include Canyon Owl, Brown-eyed Owl, Wood Owl, and Hoot Owl.

The Spotted Owl is a nocturnal, woodland owl and is darkly coloured, with a round head , and dark brown eyes. Their brown plumage is heavily spotted with white on the breast and belly, with less spots on the wings, back, and head. The pale brown facial disks are concentrically ringed with dark brown. The eyebrows, lores, and bill are greyish. Its plumage is soft and fluffy, which can make the head appear oversized. Spotted Owls are placid owls, allowing close approach by humans and may be reluctant to fly. In flight, they have heavy methodical wing beats, but appear buoyant for their size. When roosting, a Spotted Owl will sit on a branch, near the trunk, where it is camouflaged against tree bark and shadows.

Length: average 48cm (19") for females, 46cm (18") for males.
Wingspan: average 109cm (43") for females, 106cm (42") for males.
Weight: 518-760g (1-1.75 lbs)

[Image: image004.jpg]

1. Californian Spotted Owl (Strix occidentalis occidentalis)
Distribution: Nevada, Central and South California.
2. Northern Spotted Owl (Strix occidentalis caurina
Description: Darker than nominate race.
Size: Wing length 31.5-32.5 cm, Tail length 19-21.3 cm.
Distribution: British Columbia to North California.
3. Mexican Spotted Owl (Strix occidentalis lucida)
Some suggest this may be a seperate species: Mountain Forest Owl - Strix lucida.
Description: Lighter than nominiate race, and more profusely spotted white.
Distribution: Arizona, New Mexico, South-west Texas to Central Mexico.
4. 'Spotted Owl' (Strix occidentalis juanaphillipsae)
No common name.

North America - Resident in the mountains and in the humid coastal forest from southwestern mainland British Columbia south through western Washington and western Oregon to southern California; and in the Rocky Mountain region of the interior from southern Utah and southwestern and south-central Colorado south through the mountains of Arizona, New Mexico, and extreme northwestern Texas. The Spotted Owl is generally nonmigratory, except that some downslope movement from mountains may occur in winter.

The Spotted Owl is a bird of dense, dark, old-growth or mixed mature and old-growth coniferous forests. Forests are usually dominated by firs or Douglas-fir, but they also use mature hardwood forests of cottonwoods, alders, oak, and sycamore, especially along steep-walled river valleys. They prefer an uneven and multilayered canopy. They prefer shaded mountain slopes and canyons over flat plateau areas.

A nocturnal and rather "tame" bird. Roosts in deep shade during the day. 

The typical advertisement call is a mellow, 4-note hoot, "Whoop wu-hu hoo". Both Males and Females use it as a territorial call and mate-locating call. During territorial disputes, they give a more excited version of the call. Other calls are the "series location call", a series of 7 to 15 hoots, given during disputes and/or calls between paired birds. A "bark series" of 3 to 7 loud, rapid barks, usually given by the female during territorial squabbles, and then there is the "nest call" given during the pre-nesting period. Other sounds given when alarmed include grunts, groans, and chatters. The female often emits a loud "co-weeep" to contact her mate.

Hunting & Food
Hunting is done mainly at night, usually beginning just after sunset and ending a half hour before sunrise. Spotted Owls us a perch to "sit and wait" to dive down onto prey. They rarely forage in flight. Prey is sometimes cached for later use. Prey taken to the nest by the male is often decapitated first. During the day, a Spotted Owl may take the odd prey that passes by its day roost, fly to a food cache, or fly to a nearby stream to drink. Spotted Owls feed mainly on flying squirrels and wood rats. These prey are necessary for successful breeding. Other major prey include gophers, rabbits and hares. Summer diets are more varied with deer mice and voles being important foods. Spotted Owls are known to capture 30 mammal species including bats, and 23 bird species as prey. They also eat snakes, crickets, beetles, and moths. They have been known to walk around campgrounds at night to pick up scraps of food.
Pellets are large and compact measuring about 5.1 to 7.6 centimetres (2 to 3 inches) in length. Pellets contain numerous bones, skulls, and teeth, and are held together by fur and mucus.

[Image: northernspottedowl.jpg]

The breeding season is from March to September. Timing and success in producing offspring are strongly linked to the availability of prey, and not all pairs breed every year. Spotted owl pairs mate for life, but a new mate is readily taken if the other disappears. They probably begin breeding at two to three years of age.
Spotted Owls nest primarily in stick nests of Northern Goshawks, on clumps of mistletoe, in large tree cavities, on broken tops of large trees, on large branches, or cavities in banks and rock faces. Old nests are not repaired before eggs are laid, and tend to be reused year after year. Clutch size ranges from 2 to 4 eggs, but averages 2 to 3 eggs. Eggs are laid every 3 to 4 days, usually in April. The female does all incubation and the male delivers food to the nest. The incubation period is about 28 to 32 days. Unlike most other owls, Spotted Owls may not defend their eggs and young from predators, watching nearby as the nest is destroyed. Young are brooded constantly by the female for 2 weeks, then she begins to hunt as well. The male brings food to the nest and passes it to the female to feed to the young. Young start roaming from the nest onto nearby branches at about 5 weeks, but some flutter to the ground before climbing up into trees. They can fly weakly at about 6 weeks. At 9 to 10 weeks young can capture insect prey by themselves. Families remain loosely associated during summer before young disperse in the autumn. Adults tend to remain near their traditional nesting territories, while juveniles disperse widely, as much as 100 to 200 kilometres (60 to 125 miles).

Spotted Owls are long-lived, with captive Owls of 21 years being known.
Mortality in the wild is thought to be very high (60 to 95%) for juveniles, especially during the dispersal stage. Adult mortality is estimated at 5 to 20% annually. Natural predators of the Spotted Owl include the Great Horned Owl, which preys on both adults and young; the red-tailed hawk, which preys on young; and the common raven, which may destroy eggs. Many juveniles starve to death.
It is thought that Barred Owls will out-compete Spotted Owls for habitat, by being more aggressive, when the two species come into contact. 
The Spotted Owl may be the most publicised of all endangered species in North America. Because of its dependence on large tracts of old-growth coniferous forests, management for this owl has caused tremendous turmoil in the forest harvesting industry, and has spawned an incredible amount of research - too much to go into here.

Uncertain. Locally threatened by forest destruction, and by hybridisation with the Barred Owl Strix varia.
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  • Claudiu Constantin Nicolaescu
New Threat To Spotted Owl Exposed

ScienceDaily (May 27, 2008) — A new study provides a baseline distribution of blood parasites and strains in Spotted Owls, suggesting a more fragile immune health than previously understood for the already threatened Northern and California Spotted Owls.

The study, co-authored by San Francisco State University biologists, is the first to show a Spotted Owl infected with an avian malaria (Plasmodium) parasite.

"While Plasmodium parasites have been found in thriving owl species, the detection in a Spotted Owl could further challenge the threatened species' survival," said Heather Ishak, an SF State graduate biology student who performed the research with Assistant Professor of Biology Ravinder Sehgal and others.

Ishak conducted the study as part of a larger investigation into blood-borne parasites in birds of prey. She searched for three types of blood parasites in 111 Spotted Owls, 44 Barred Owls (Strix varia) and 387 birds representing nine other owl species. The blood analysis involving DNA testing revealed that 44 percent of Northern and California Spotted Owl subspecies harbored 17 strains of blood parasites.

They also harbored an unusually high number of strains that were not found in the other owl species.

"The controversy over the spotted owl's habitat in old-growth forests over the past two decades has made this species one of the most intensely researched birds in the world," Sehgal said. "Prior to this discovery however, the question of which blood parasites they harbor and whether Barred Owls could be a source of diseases that could further limit the Spotted Owl's chance of survival had been largely unaddressed."

According to the researchers, the infected Northern Spotted Owl (Strix occidentalis caurina) may have been exposed to the parasite by coming into contact with mosquitoes that fed on a Barred Owl (Strix varia). The increasingly invasive Barred Owls compete with Spotted Owls for food and nesting sites.

Ishak and Sehgal expect their findings will prompt more research into this species and enhance general knowledge of the role and effects of blood-borne pathogens in wild bird populations.

[Image: 080527201811-large.jpg]
Spotted owl. A new study provides a baseline distribution of blood parasites and strains in Spotted Owls, suggesting a more fragile immune health than previously understood for the already threatened Northern and California Spotted Owls.
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  • Claudiu Constantin Nicolaescu
Threatened Owls Pushed Out of Home by Foes

By Megan Gannon, News Editor | February 25, 2014 06:03pm ET

[Image: spottedowledited.jpg]
The northern spotted owl was championed by environmental groups who sought to see it protected. 

A threatened species of owl is losing a turf war in the Pacific Northwest.

Northern spotted owls are getting edged out of their already declining habitat by invading barred owls, a new study finds.

Researchers pored over 22 years of data from a study site in Oregon covering 386 square miles (1,000 square kilometers) where the habitats of the two species overlap. In this area, both owl species were more likely to abandon a neighborhood when their rival was present, the researchers found.

Northern spotted owls (Strix occidentalis caurina), whose numbers have been declining, were more sensitive to this competition, the study revealed. Meanwhile, barred owls (Strix varia), which have more offspring and a more diverse diet and use of habitat, have experienced a population boom.

"Scientists in other parts of the Pacific Northwest have suggested that differences in the habitat preferences of the barred owl and spotted owl might allow them to coexist," study author Charles Yackulic, a research statistician with the U.S. Geological Survey, said in a statement. "While the two species showed different habitat preferences in this study site, there is still substantial overlap in habitat use. As a result, in recent years, barred owls have frequently excluded spotted owls from habitat that they would otherwise prefer."

When spotted owls are forced to leave their preferred neighborhood, the birds sometimes take up residency in a less suitable habitat where they might not have as much success reproducing, the researchers say.

Besides competition with barred owls, spotted owls are threatened by a loss of old-growth forest habitat in California, Oregon and Washington. In another recent setback for the species, rat poison used in illegal marijuana farms in Northern California killed a few of the birds. The nocturnal creatures are listed as threatened under the U.S. Endangered Species Act. There are estimated to be less than 4,000 breeding pairs from southwestern British Columbia, in Canada, to northern California, according to the International Union for Conservation of Nature (IUCN).

Yackulic and colleagues also used a computer model to project future population dynamics of the two species. They found that barred owls are likely to push spotted owl numbers even lower over the next few decades.

"The results of the model show that should the barred owl population be reduced to about a quarter of its current size through management actions, it would minimize the costs associated with managing barred owl populations indefinitely, while also providing substantial benefits to the spotted owl population," Yackulic said. 

The findings were detailed in the journal Ecology this month.

Charles B. Yackulic, Janice Reid, James D. Nichols, James E. Hines, Raymond Davis, and Eric Forsman 2014. The roles of competition and habitat in the dynamics of populations and species distributions. Ecology 95:265–279.

The role of competition in structuring biotic communities at fine spatial scales is well known from detailed process-based studies. Our understanding of competition's importance at broader scales is less resolved and mainly based on static species distribution maps. Here, we bridge this gap by examining the joint occupancy dynamics of an invading species (Barred Owl, Strix varia) and a resident species (Northern Spotted Owl, Strix occidentalis caurina) in a 1000-km2 study area over a 22-year period. Past studies of these competitors have focused on the dynamics of one species at a time, hindering efforts to parse out the roles of habitat and competition and to forecast the future of the resident species. In addition, while these studies accounted for the imperfect detection of the focal species, no multi-season analysis of these species has accounted for the imperfect detection of the secondary species, potentially biasing inference. We analyzed survey data using models that combine the general multistate–multi-season occupancy modeling framework with autologistic modeling, allowing us to account for important aspects of our study system.
We found that local extinction probability increases for each species when the other is present; however, the effect of the invader on the resident is greater. Although the species prefer different habitats, these habitats are highly correlated at the patch scale, and the impacts of invader on the resident are greatest in patches that would otherwise be optimal. As a consequence, competition leads to a weaker relationship between habitat and Northern Spotted Owl occupancy. Colonization and extinction rates of the invader are closely related to neighborhood occupancy, and over the first half of the study the availability of colonists limited the rate of population growth. Competition is likely to exclude the resident species, both through its immediate effects on local extinction and by indirectly lowering colonization rates as Northern Spotted Owl occupancy declines. Our analysis suggests that dispersal limitation affects both the invasion dynamics and the scale at which the effects of competition are observed. We also provide predictions regarding the potential costs and benefits of managing Barred Owl populations at different target levels.
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  • Claudiu Constantin Nicolaescu
Genome of threatened northern spotted owl assembed
Genome completion will help researchers better measure interbreeding among hybrid owls and guide conservation priorities in the West

Date: September 5, 2017
Source: California Academy of Sciences

[Image: 170905111407_1_900x600.jpg]
An adult northern spotted owl (Strix occidentalis caurina).
Credit: Jack Dumbacher © 2017 California Academy of Sciences

A charismatic owl iconic to Pacific Coast forests is no longer ruling the roost, and scientists now have another tool for understanding its decline. Researchers have assembled the California Academy of Sciences' first-ever animal genome after sequencing the DNA of the northern spotted owl (Strix occidentalis caurina). In collaboration with the University of California Berkeley (UC Berkeley), University of California San Francisco (UCSF), the National Museum of Natural History in Paris, and the Howard Hughes Medical Institute, Academy scientists extensively mapped the bird's genetic material to better understand how this threatened forest dweller is interacting with non-native owls invading its habitat. Findings are published this month in Genome Biology and Evolution.

"The northern spotted owl is special because it's our backyard bird here in the Bay Area -- found from Marin County, California all the way north to British Columbia," Dr. Jack Dumbacher says, Academy curator of ornithology and mammalogy.

Marked by white spots across a brown chest, the northern spotted owl vocalizes two to three short hoots followed by a longer hooooo from its perch on centuries-old trees in old-growth forests. But standing at a foot-and-a-half tall, this top predator is now rarely seen or heard. The bird experienced a rapid decline and has been federally listed as threatened under the Endangered Species Act since 1990.

"We've really seen a perfect storm with many factors complicating the northern spotted owl's recovery," Dumbacher says. But this storm is unprecedented, so researchers are working to track how it unfolds in forests across the West.

Understanding a shifting power dynamic

Over the past half-century, the barred owl (Strix varia) -- a close relative formerly found east of the Rocky Mountains -- has flown onto the scene. Notable for its larger size and more aggressive behavior, barred owls have vertical dark markings against a white belly and a hooting call birders mimic with the words, "Who cooks for you?"

Barred and northern spotted owls now have overlapping geographic ranges and compete with one another for prey and breeding territories. To complicate matters, timber harvest has reduced available habitat for both species. The barred owl is the scrappier of the two, enjoying a more varied diet and producing more young, more often -- ultimately emerging as the super competitor.

"We wanted to know how the barred owl's range expansion will play out evolutionarily," Zachary Hanna says, lead author and Academy-affiliated student who is currently a PhD candidate at UC Berkeley in the Museum of Vertebrate Zoology. Scientists have noticed barred and spotted owls interbreeding and hatching hybrid offspring since the late 1980s.

"I think we're going to see more hybridization in the future," Hanna adds, "so these owls are serving as a case study for how species that have been isolated for millions of years might interact in the face of a rapidly changing world."

Bay Area owl becomes a species ambassador

Barred owls were first recorded in Marin County in 2003. In 2005, an injured northern spotted owlet was ushered in to WildCare, a wildlife rehabilitation center in San Rafael, California, for assistance. The female (later named Sequoia) was deemed unfit for release back into the wild. Her healed injuries had resulted in noisy flight and she could no longer successfully hunt prey.

Sequoia showed no plumage or vocalizations that would indicate telltale signs of a hybrid, meaning she was an indisputable representative of her species. The research team took a small blood sample during one of Sequoia's routine physicals and extracted enough DNA to get a clear understanding of her genetic identification.

"The advanced genetic techniques we used to sequence Sequoia's DNA are much like shredding a book and putting it back together again using overlapping sentences," Dumbacher says. Hanna applied new sequencing strategies to read millions of short genetic regions and used powerful computers and assembly software to compile the genome again.

In addition to Sequoia, the team also sequenced a barred owl individual from the eastern United States as a baseline of comparison for better evaluating the frequency of interbreeding and tracking hybrid offspring in the wild. Researchers now have the genetic tools to perform a variety of analyses, and hopefully understand whether interbreeding between barred owls might directly threaten the extinction of northern spotted owls.

Shedding light on night vision

In addition to tackling critical conservation questions, this landmark assembly of the northern spotted owl's genome has allowed scientists to better understand the evolution of night vision across bird species. Several previous studies suggested that owls lost various color receptors in their eyes over time. The research team has used the full genome to search for and confirm that genes responsible for color receptors are indeed absent in owls.

"Much like cave salamanders that have lost their eyes after being in the dark, owls too appear to have lost their violet opsin -- the receptor birds use to see violet and ultraviolet light," Dumbacher says. But, strikingly, genetic analysis revealed that owls still have a capacity to discriminate color (although it's greatly reduced from that of ancestral birds). In fact, owls still retain more of their light and color sensitivity than most mammals.

The research team hopes that the sequenced genome will doubly inform the evolution of night vision in birds as well as broader conservation strategies for the northern spotted owl -- ensuring this nocturnal predator calls hoot-hoothoot-hooooo across its native forests for generations to come.

Story Source: California Academy of Sciences. "Genome of threatened northern spotted owl assembed: Genome completion will help researchers better measure interbreeding among hybrid owls and guide conservation priorities in the West." ScienceDaily. (accessed September 6, 2017).

Journal Reference:
Zachary R. Hanna, James B. Henderson, Jeffrey D. Wall, Christopher A. Emerling, Jérôme Fuchs, Charles Runckel, David P. Mindell, Rauri C. K. Bowie, Joseph L. DeRisi, John P. Dumbacher. Northern spotted owl (Strix occidentalis caurina) genome: divergence with the barred owl (Strix varia) and characterization of light-associated genes.Genome Biology and Evolution, 2017; DOI: 10.1093/gbe/evx158

We report here the assembly of a northern spotted owl (Strix occidentalis caurina) genome. We generated Illumina paired-end sequence data at 90X coverage using nine libraries with insert lengths ranging from approximately 250 - 9,600 nucleotides and read lengths from 100-375 nucleotides. The genome assembly is comprised of 8,108 scaffolds totaling 1.26 × 109 nucleotides in length with an N50 length of 3.98 × 106 nucleotides. We calculated the genome-wide fixation index (FST) of S. o. caurina with the closely related barred owl (S. varia) as 0.819. We examined nineteen genes that encode proteins with light-dependent functions in our genome assembly as well as in that of the barn owl (Tyto alba). We present genomic evidence for loss of three of these in S. o. caurina and four in T. alba. We suggest that most light-associated gene functions have been maintained in owls and their loss has not proceeded to the same extent as in other historically dim-light-adapted vertebrates.
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  • Claudiu Constantin Nicolaescu
Marijuana farms expose spotted owls to rat poison in northwest California
As timberland converts to cannabis, spotted owls and barred owls test positive for rat poison

Date: January 11, 2018
Source: University of California - Davis

[Image: 180111141657_1_900x600.jpg]
Jack Dumbacher with the owl collection at the California Academy of Sciences.
Credit: 2017 California Academy of Sciences

Wildlife species are being exposed to high levels of rat poison in northwest California, with illegal marijuana farms the most likely source point, according to a study led by the University of California, Davis, with the California Academy of Sciences.

The study, released Jan. 11 in the journal Avian Conservation and Ecology, showed that seven of the 10 Northern spotted owls collected tested positive for rat poison, while 40 percent of 84 barred owls collected also tested positive for the poison.

The study is the first published account of anticoagulant rodenticide in Northern spotted owls, which are listed as a threatened species under federal and state Endangered Species acts.

The study area encompasses Humboldt, Mendocino and Del Norte counties. It supports previous accounts that rat poison is contaminating the food web in this region, as the primary food source for owls-rodents -- is being contaminated.

Timberland Converting to Marijuana Farms

Driving the issue is the increasing conversion of private timberland into private, illegal and unpermitted marijuana cultivation sites. These sites often overlap with designated critical habitat for Northern spotted owls, and the owls feed at their edges.

"Spotted owls are inclined to feed along forest edges. Because grow sites break apart these forest landscapes, they are likely source points for exposure," said lead author Mourad Gabriel, a research faculty member with the UC Davis Karen C. Drayer Wildlife Health Center within the School of Veterinary Medicine's One Health Institute. He's also executive director of nonprofit Integral Ecology Research Center.

Gabriel's studies in 2012, 2013 and 2015 were the first to link rat poison and illegal marijuana farms to the deaths of fishers, a weasel-like mammal living in remote forests of California and the Pacific Northwest, bringing broad attention to the issue.

Abundance of Grow Sites, Lack of Oversight

Proposition 64, which legalizes recreational marijuana in the state, took effect this month. With its arrival, resource managers expect the number and size of unpermitted, private cultivation sites to grow, which could exacerbate the problem.

The study authors note that an estimated 4,500 -- 15,000 private cultivation sites are in Humboldt County alone, yet the county has seen legal permits for only a small fraction of them. That means there are thousands of unpermitted private grow sites with no management oversight.

"When you have thousands of unpermitted grows and only a handful of biologists that regulate that for multiple counties, we're deeply concerned that there aren't sufficient conservation protective measures in place," Gabriel said. "If no one is investigating the level at which private marijuana cultivators are placing chemicals out there, the fragmented forest landscapes created by these sites can serve as source points of exposure for owls and other wildlife."

Anticoagulant rodenticides inhibit the ability of mammals and birds to recycle vitamin K. This creates a series of clotting and coagulation problems, which can lead to uncontrollable internal bleeding.

Barred Owls and Added Stressors

Barred owls are a physically larger group of owls currently competing for resources and space in critical habitat designated for Northern spotted owls. Forty percent, or 34 of the 84, of the barred owl tissue samples collected for this study tested positive for anticoagulant rodenticide. The owls are being exposed through the prey they eat.

Environmental contamination, when coupled with ongoing competition from barred owls, poses an additional stressor on Northern spotted owls, the study said. The fact that barred owls are contaminated as well shows that the species may be used as potential surrogates for detecting these contaminants in Northern spotted owls.

"Access to these owl specimens allows us to explore the health of the entire regional forest system," says Jack Dumbacher, Curator of Ornithology and Mammalogy at the California Academy of Sciences. "We're using our collections to build a concrete scientific case for increased forest monitoring and species protection before it's too late to intervene."

This study's researchers did not kill any owls for this study. Northern spotted owls were opportunistically collected when found dead in the field, while barred owl tissue samples were provided by outside investigators conducting an unrelated barred-owl project.

The necropsies for this study were conducted at the California Academy of Sciences and the California Animal Health and Food Safety Laboratory System, which is part of the UC Davis School of Veterinary Medicine.

Additional co-authoring institutions include Green Diamond Resource Company, Hoopa Valley Tribe and Humboldt State University.

The study was funded by the United States Fish and Wildlife Service, Arcata and Yreka California Field Offices.

Story Source: University of California - Davis. "Marijuana farms expose spotted owls to rat poison in northwest California: As timberland converts to cannabis, spotted owls and barred owls test positive for rat poison." ScienceDaily. (accessed January 11, 2018).

Journal Reference:
Mourad W. Gabriel, Lowell V. Diller, John P. Dumbacher, Greta M. Wengert, John M. Higley, Robert H. Poppenga, Shannon Mendia. Exposure to rodenticides in Northern Spotted and Barred Owls on remote forest lands in northwestern California: evidence of food web contamination. Avian Conservation and Ecology, 2018; 13 (1) DOI: 10.5751/ACE-01134-130102

The documentation of anticoagulant rodenticides (AR) in nontarget species has centered around wildlife that inhabit urban or agricultural settings. However, recent studies in California have shown that AR use in remote forest settings has escalated and has exposed and killed forest carnivores. Anticoagulant rodenticides have been documented as physiological stressors for avian species. Northern Spotted Owl (Strix occidentalis caurina) critical and occupied habitat overlaps the areas where these studies occurred, yet no data were previously available to demonstrate whether this species was similarly affected. We investigated whether avian predators are also exposed to these specific pesticides and whether Barred Owls (Strix varia) may be a surrogate to indicate exposure rates in Northern Spotted Owls. We documented that 70% of Northern Spotted Owls and 40% of Barred Owls were exposed to one or more anticoagulant rodenticides. None of the rodent prey species sampled within the study area were positive for ARs. There were no spatial clusters for either low or high rates of exposure, though we detected low temporal trend early on throughout the study area. We hypothesize a recent change in land-use toward marijuana cultivation may have led to the increased use of AR in this area. This study demonstrates environmental contamination within occupied Northern Spotted Owl habitat and that Barred Owls can be used as adequate surrogates for detecting these pollutants in a rare species such as the Northern Spotted Owl. Furthermore, additional studies should focus on whether these pesticides are also affecting prey availability for these forest avian species.
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  • Claudiu Constantin Nicolaescu
Owls against owls in a challenge for survival

Researchers forecast interactions between two owl species and the quality of their habitat in the Pacific Northwest

Date: March 5, 2019
Source: Ecological Society of America

[Image: 190305153659_1_900x600.jpg]
A northern spotted owl peers down from an old-growth forest in the Pacific Northwest.
Credit: Photo courtesy of Charles Yackulic/US Forest Service - Pacific Northwest Research Station

Scientists are puzzling out how to address the declining numbers of northern spotted owls (NSO) in their Pacific Northwest forest habitat. A new study in the Ecological Society of America's journal Ecological Applications explores the reasons why spotted owls are losing a foothold in their habitat, forecasts future habitat conditions and species interactions, and suggests best management practices.
The U.S Fish and Wildlife Service first listed the species as "threatened" under the Endangered Species Act in the late 20thcentury because years of over-logging left the owls' forest home degraded. The U.S Forest Service and the Bureau of Land Manangemnet began actively managing federal lands using the 1994 Northwest Forest Plan that focuses on preserving and increasing the acreage of the spotted owls' preferred mature forests habitat.
While some restoration of the forest is occurring, there are other pressures affecting the forests like the 2002 Biscuit Fire that burned nearly 500,000 acres in southern Oregon and northern California. From the beginning of the implementation of the 1994 plan, managers expected owl populations to continue declining because regrowth and recovery of old forest is a slow process that occurs over decades.
And yet, even with those projections, mangers and ecologists are surprised NSO populations are decreasing at a greater rate than anticipated. The reason? The northern spotted owls are not alone in their forests.
Barred owls began to invade the northern portion of spotted owl's range about 50 years ago and existed in low numbers in 1994 when the Northwest Forest Plan went into effect. Unfortunately, barred owls are an invasive species and increase quickly in numbers.
"We have known for some time that NSO are reliant on older forest as habitat, that recovering NSO would require recovering this habitat, and that this process of recovery would take many decades," says lead author Charles Yackulic of the U.S. Geological Survey. "Twenty-five years ago, however, we did not anticipate the increases in barred owl abundances would lead to a second major threat to NSO recovery."
The invading barred owl competes with the spotted owl for prime nesting spots and hunting areas. The barred owl is winning the fight and may push the spotted owl to localized extinction in the region in the next few decades without managers intervening. The barred owl is changing the entire ecosystem, so other animals in the forest are losing along with the spotted owl.
"NSO are only found in the Pacific Northwest and play a unique role in the food webs of intact forest in this region," explains Yackulic. "While barred owls serve some similar ecological functions, they eat a broader range of prey and there is evidence their invasion is leading to trophic cascades -- unexpected declines in other members of the ecological communities because of differences in how NSO versus barred owls interact with food webs."
In the paper, the researchers analyze the relative importance of habitat conditions and barred owl competition in past and future NSO territorial population dynamics in eleven study areas. They also forecast the future interactions between the two owl species under current management conditions and under scenarios with various levels of barred owl removal or changes in habitat.
They find that recent wide-range declines in NSO occupancy are driven primarily by competition with increasing barred owl populations and removal of barred owls is an effective management option to prevent declines in the near future.
But barred owl removal is not enough on its own, either. While barred owl removal could stabilize NSO populations in the short-term, forest regeneration can take 50 or more years. Maintaining or improving habitat conditions is an important factor in promoting spotted owl survival over longer periods and allows managers to be less reliant on barred owl removals in the future.
In short, spotted owl populations survival may depend on managers' using a two-fold approach of removing barred owls in the short term and preserving the forests in the long run. The researchers project this combination results in a 95 percent probability that spotted owls will persist in these areas for 50 or more years -- a best-case scenario. However, without either practice, if habitat conditions worsen and barred owls are not removed at all, spotted owls will be extinct from many of the study areas within decades.
In the future, the researchers hope to understand how to effectively use barred owl removal methods, and where to prioritize them. They also want to identify if any habitat conditions can support both owl species. Who knows -- there may be situations under which NSO can coexist with barred owls, and the two can manage to get along.

Story Source:  Ecological Society of America. "Owls against owls in a challenge for survival: Researchers forecast interactions between two owl species and the quality of their habitat in the Pacific Northwest." ScienceDaily. (accessed March 7, 2019).

Journal Reference:
  1. Yackulic, Charles, et al. The past and future roles of competition and habitat in the range-wide occupancy dynamics of Northern Spotted Owls. Ecological Applications, 2019 DOI: 10.1002/eap.1861
Slow ecological processes challenge conservation. Short‐term variability can obscure the importance of slower processes that may ultimately determine the state of a system. Furthermore, management actions with slow responses can be hard to justify. One response to slow processes is to explicitly concentrate analysis on state dynamics. Here, we focus on identifying drivers of Northern Spotted Owl (Strix occidentalis caurina) territorial occupancy dynamics across 11 study areas spanning their geographic range and forecasting response to potential management actions. Competition with Barred Owls (Strix varia) has increased Spotted Owl territory extinction probabilities across all study areas and driven recent declines in Spotted Owl populations. Without management intervention, the Northern Spotted Owl subspecies will be extirpated from parts of its current range within decades. In the short term, Barred Owl removal can be effective. Over longer time spans, however, maintaining or improving habitat conditions can help promote the persistence of northern spotted owl populations. In most study areas, habitat effects on expected Northern Spotted Owl territorial occupancy are actually greater than the effects of competition from Barred Owls. This study suggests how intensive management actions (removal of a competitor) with rapid results can complement a slower management action (i.e., promoting forest succession).

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  • Claudiu Constantin Nicolaescu
Old-growth forest may provide valuable biodiversity refuge in areas at risk of severe fire

by USDA Forest Service

[Image: oldgrowthfor.jpg]
A northern spotted owl. Credit: USDA Forest Service photo by Damon Lesmeister

New findings show that old-growth forests, a critical nesting habitat for threatened northern spotted owls, are less likely to experience high-severity fire than young-growth forests during wildfires. This suggests that old-growth forest could be leveraged to provide valuable fire refuges that support forest biodiversity and buffer the extreme effects of climate change on fire regimes in the Pacific Northwest.
A recent study published in the journal Ecosphere examined the impact of the Douglas Complex and Big Windy fires that burned in the Klamath-Siskiyou region of Oregon during July 2013, a drought year. The fires burned through a long-term study area for northern spotted owls. Using information on forest vegetation before and after the fires, along with known spotted owl nesting areas, researchers had an unprecedented chance to compare the impact of wildfire on critical old-growth nesting habitat.
"On federally managed lands, spotted owl nesting habitat is largely protected from timber harvest under the Northwest Forest Plan, but wildfire is still a primary threat to the old-growth forest that spotted owls rely on for nesting habitat," said research wildlife biologist Damon Lesmeister. "The loss of spotted owl nesting habitat as a result of severe fire damage could have significant negative impacts on the remaining spotted owl populations as well as a large number of other wildlife species that rely on these old forests."
Old-growth forests have more vegetation than younger forests. Researchers expected that this meant more fuel would be available for wildfires, increasing the susceptibility of old-growth forests to severe fire, high tree mortality, and resulting loss of critical spotted owl nesting habitat. However, the data suggested a different effect.
Lesmeister and his colleagues classified fire severity based on the percentage of trees lost in a fire, considering forest that lost less than 20% of its trees to fire subject to low-severity fire and those with more than 90% tree loss subject to high-severity fire. They found that old-growth forest was up to three times more likely to burn at low severity—a level that avoided loss of spotted owl nesting habitat and is generally considered to be part of a healthy forest ecosystem.
"Somewhat to our surprise, we found that, compared to other forest types within the burned area, old-growth forests burned on average much cooler than younger forests, which were more likely to experience high-severity fire. How this actually plays out during a mixed-severity wildfire makes sense when you consider the qualities of old-growth forest that can limit severe wildfire ignitions and burn temperatures, like shading from multilayer canopies, cooler temperatures, moist air and soil as well as larger, hardier trees."
Because old-growth forests may be refuges of low-severity fire on a landscape that experiences moderate to high-severity fires frequently, they could be integral as biodiversity refuges in an increasingly fire-prone region. Leveraging the potential of old-growth forests to act as refuges may be an effective tool for forest managers as they deal with worsening fire seasons in the Pacific Northwest.

Journal Reference:
Damon B. Lesmeister et al, Mixed‐severity wildfire and habitat of an old‐forest obligate, Ecosphere (2019). DOI: 10.1002/ecs2.2696

The frequency, extent, and severity of wildfire strongly influence the structure and function of ecosystems. Mixed‐severity fire regimes are the most complex and least understood fire regimes, and variability of fire severity can occur at fine spatial and temporal scales, depending on previous disturbance history, topography, fuel continuity, vegetation type, and weather. During high fire weather in 2013, a complex of mixed‐severity wildfires burned across multiple ownerships within the Klamath‐Siskiyou ecoregion of southwestern Oregon where northern spotted owl (Strix occidentalis caurina) demographics were studied since 1990. A year prior to these wildfires, high‐resolution, remotely sensed forest structural information derived from light detection and ranging (lidar) data was acquired for an area that fully covered the extent of these fires. To quantify wildfire impact on northern spotted owl nesting/roosting habitat, we fit a relative habitat suitability model based on pre‐fire locations used for nesting and roosting, and forest structure variables developed from 2012 lidar data. Our pre‐fire habitat suitability model predicted nesting/roosting locations well, and variable response functions followed known resource selection patterns. These forests had typical characteristics of old‐growth forest, with high density of large live trees, high canopy cover, and complex structure in canopy height. We projected the pre‐fire model onto lidar data collected two months post‐fire to produce a post‐fire suitability map, which indicated that >93% of pre‐fire habitat that burned at high severity was no longer suitable forest for nesting and roosting. We also quantified the probability that pre‐fire nesting/roosting habitat would burn at each severity class (unburned/low, low, moderate, high). Pre‐fire nesting/roosting habitat had lower probability of burning at moderate or high severity compared to other forest types under high burning conditions. Our results indicate that northern spotted owl habitat can buffer the negative effects of climate change by enhancing biodiversity and resistance to high‐severity fires, which are predicted to increase in frequency and extent with climate change. Within this region, protecting large blocks of old forests could be an integral component of management plans that successfully maintain variability of forests in this mixed‐ownership and mixed‐severity fire regime landscape and enhance conservation of many species.

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  • Claudiu Constantin Nicolaescu
Despite habitat protection, endangered owls decline in Mount Rainier National Park

Date: August 8, 2019
Source: American Ornithological Society Publications Office

When the Northern Spotted Owl was protected under the Endangered Species Act in 1990, the primary threat to the species was the loss of the old-growth forest it depends on. However, new research published in The Condor: Ornithological Applications shows that the Northern Spotted Owl population in Washington's Mount Rainier National Park has declined sharply in the past two decades despite the long-term preservation of habitat within the park. The culprit? The spread of Barred Owls, a closely related, competing species that has moved into Spotted Owls' range from the east.

Biologists have seen Barred Owls in Spotted Owl territories within the national park more and more frequently since Spotted Owl surveys began in 1997. For their new study, Oregon Cooperative Fish and Wildlife Research Unit's Anna Mangan, the National Park Service's Tara Chestnut, and their colleagues analyzed two decades' worth of data from these surveys. "We found that Spotted Owls now occupy 50% fewer territories in the park than they did 20 years ago when the study began, despite the lack of habitat disturbance," says Chestnut. "Spotted Owls were less likely to be present in territories where Barred Owls were detected, and if Spotted Owls were there, sharing space with Barred Owls made them less likely to breed. Only 18 adult Spotted Owls were detected in the study area in 2016, down from a high of 30 owls in 1998."

"Barred Owls eat a wider range of foods and use a greater variety of forested habitats, including the old-growth forest required by Spotted Owls, and these generalist traits have aided them in their highly successful range expansion throughout the Pacific Northwest," explains co-author Katie Dugger, a researcher the US Geological Survey's Oregon Cooperative Fish and Wildlife Research Unit. "Barred Owls are now competing with Northern Spotted Owls for food and space, and increased Barred Owl densities are associated with declines in Northern Spotted Owl populations across their range."

"What is particularly alarming is that this decline has occurred even at Mount Rainier, where Spotted Owl habitat has been protected for over 100 years, with virtually no fire or logging disturbance," says Mangan. "With Barred Owls detected at nearly every Spotted Owl territory monitored in the park, the future of Spotted Owls at Mount Rainier is tenuous. It also suggests that preserving owl habitat, while still crucial, is likely no longer enough to sustain the Spotted Owl population at Mount Rainier."

If current trends continue, scientists predict that the Spotted Owl could be extinct in the region within approximately six to eight decades. "Conservation managers can focus on protecting old-growth habitat with steeper slopes, as we found this to have higher Spotted Owl occupancy, and can continue to monitor Barred Owl populations to better understand their effect on local Spotted Owl populations," adds Mangan. "Managers will need to consider some creative solutions, and likely some unpopular choices, if the Northern Spotted Owl is going to be prevented from going extinct on public lands."

Story Source: American Ornithological Society Publications Office. "Despite habitat protection, endangered owls decline in Mount Rainier National Park." ScienceDaily. (accessed August 8, 2019).

Journal Reference:
Anna O Mangan, Tara Chestnut, Jody C Vogeler, Ian K Breckheimer, Wendy M King, Keith E Bagnall, Katie M Dugger. Barred Owls reduce occupancy and breeding propensity of Northern Spotted Owl in a Washington old-growth forest. The Condor, 2019; DOI: 10.1093/condor/duz031

Protected lands like national parks are important refuges for threatened and endangered species as environmental pressures on wildlife and their habitats increase. The Northern Spotted Owl ( Strix occidentalis caurina ), a species designated as threatened under the Endangered Species Act, occurs on public lands throughout the western United States including Mount Rainier National Park (MRNP), Washington. With virtually no history of timber harvest or large forest disturbance within MRNP boundaries since the park's creation in 1899, MRNP provides an ideal place to evaluate potential impacts of climate change and invasive Barred Owls ( Strix varia) on the Northern Spotted Owl. We used a multi-state, multi-season occupancy model to investigate how Northern Spotted Owl occupancy dynamics and breeding propensity are related to the presence of Barred Owls, local and regional weather, and habitat characteristics at MRNP from 1997 to 2016. Historical occupancy of Northern Spotted Owl breeding territories in MRNP has declined by 50% in the last 20 yr, and territory occupancy by breeding Northern Spotted Owls also decreased, reaching a low of 25% in 2016. Occupancy rates were higher on territories with steeper terrain and breeding rates were lower when Barred Owls were detected within historical territories. Our results also indicated that breeding propensity was higher when early nesting season temperatures during March and April were higher. In addition, the ability to detect breeding Northern Spotted Owls decreased when Barred Owls were present in the territory. Habitat variables from LiDAR were not correlated with Northern Spotted Owl occupancy dynamics, likely reflecting the dominance of old-growth forest in this protected park. This study illustrates the strong relationship between Barred Owls and Northern Spotted Owl demographics and breeding site selection in a landscape where habitat loss by timber harvest and fire has not occurred.
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