Special Status Species Spotlight – The Burrowing Owl

Here at Sequoia Ecological Consulting, we have the privilege of working with many incredible threatened and endangered species. In this series, we aim to go in-depth and highlight some of the magnificent creatures we work to preserve. In this installment, we will discuss the western burrowing owl (Athene cunicularia). 

The burrowing owl (BUOW) is designated a California Species of Special Concern by the California Department of Fish and Game and is federally listed as a Bird of Conservation Concern. This species also receives additional protection under the Migratory Bird Treaty Act (MBTA) and California Fish and Game Code 3503 (a section which makes it unlawful to take, possess, or needlessly destroy the nest or eggs of any bird).

Burrowing owls range throughout the Central Valley, the inner and outer Coastal regions, portions of the San Francisco Bay Area, the southern California Coast (from southern California to the Mexican Border), the Imperial Valley, and in portions of the desert and high desert habitats in southeastern and northeastern California. Burrowing owls require habitat with three basic attributes: open, well-drained terrain; short, sparse vegetation; and underground burrows.

Throughout their range burrowing owls occupy grasslands, deserts, sagebrush scrub, agricultural areas (including pastures and untilled cropland), levees and berms, coastal uplands, urban vacant lots, and even the margins of airports, golf courses, and roads. Burrowing owls rely heavily on burrows excavated by fossorial mammals and reptiles, including prairie dogs, ground squirrels, badgers, skunks, armadillos, woodchucks, foxes, coyotes, and gopher tortoises.

Where the number and availability of natural burrows are limited (for example, where burrows have been destroyed or ground squirrels have been eradicated), owls will occupy man-made drainage culverts, cavities under piles of rubble, discarded pipe, and other tunnel-like structures. Like other owl species, burrowing owls breed once each year in an extended reproductive period, during which most adults mate monogamously. Clutch sizes vary, and the number of eggs laid is proportionate to prey abundance in the environment. Burrowing owls typically feed on invertebrates, small vertebrate mammals, lizards, and birds.

The BUOW breeding season occurs from February 1 to August 31, peaking between late April and July in most years. Interestingly, burrowing owls have also been found occupying burrows in the foothills (up to 2048 feet in elevation) of California during the non-breeding, winter season. These overwintering birds do not remain during the breeding season, and typically do not breed in adjacent or nearby areas.

In the Bay Area and northern California at large, burrowing owls have been losing habitat at an alarming rate as intensive agriculture, human development, infrastructure projects, and the loss of burrowing mammal populations have greatly reduced the amount of suitable habitat for this species.

It is estimated that United States BUOW populations have declined by nearly 33% between 1966 and 2015, according to the North American Breeding Bird Survey. The declines have been most sharp in Florida, the Dakotas, and California. The remaining populations experience intense pressures from predation, human encroachment, and agricultural activities. It is therefore paramount that we work hard to protect and conserve our remaining burrowing owl populations.

Here at Sequoia, we have been actively performing burrowing owl surveys and mitigation services since our company’s inception, and we are familiar with the processes necessary to protect and conserve this emblematic species. Our hardworking biologists, such as USGS Master Bird Bander and owl specialist Julie Woodruff seen above, are passionate about working to protect this iconic bird. 

Special Status Species Spotlight – The Foothill Yellow-Legged Frog

In our ongoing series of focusing on threatened and endangered species, we aim to go in-depth and highlight some of the magnificent creatures we work to preserve. In this installment, we will discuss the foothill yellow-legged frog (Rana boylii). 

Populations of foothill yellow-legged frog (FYLF) are dispersed throughout the state of California in six “clades” labeled as the northwest/north coast, feather and upper feather river watershed, northeast/northern sierra, east/southern sierra, west/central coast, and southwest/west coast clades. In the spring of 2020, the California Fish and Game Commission officially listed five of the six clades (all but the north coast clade) of the FYLF as either endangered or threatened under the California Endangered Species Act (California ESA).

The endangered clades include south coast, west/central coast, and east/southern sierra while the threatened clades include feather river and northern sierra. The north coast clade is not currently under threat of extinction or endangerment. This listing cements the protections which this species had temporarily been afforded as a candidate for listing since 2017. Projects within the protected clades where populations of FYLF occur will now be required to avoid or mitigate impacts to FYLF populations as a California ESA listed species. 

Historically, foothill yellow-legged frogs occurred from west of the Cascade mountains in Oregon south to the Transverse ranges in Los Angeles County, and in the Sierra Nevada foothills south to Kern County. The current range now excludes coastal areas south of northern San Luis Obispo County and foothill areas south of Fresno County, where the species is assumed to be extirpated.

A medium-sized ranid frog with a slim waist, long legs, and webbing on the hind feet, adult FYLF are 1.5 – 3.2 inches long from snout to vent. Their skin is grainy and rough, featuring shades of gray, brown, and olive with occasional hints of red. The underside of the rear legs and lower abdomen are yellow, giving the frog its name. FYLF are found in or near rocky streams in a variety of habitats, such as valley foothill hardwood, valley-foothill riparian, coastal scrub, mixed conifer, mixed chaparral, and wet meadows.

This species and aquatic habitat are considered sympatric (occurring within the same geographical area), thus FYLF rarely migrate far from the streams in which they reside. FYLF eat a wide variety of invertebrates including both aquatic and terrestrial insects. They locate prey via sight then shoot out their large sticky tongue to catch their prey. This species requires shallow, flowing water in small to moderate-sized streams containing some cobble-sized rocks and portions of open canopy for basking.

Frogs deposit their egg masses on the downstream side of cobbles and boulders over which a relatively thin, gentle flow of water exists. Egg counts can range from 300-2,000 and hatch within 5-37 days depending on water temperature. Tadpoles remain around the egg mass for about a week, then move away to feed, using rocks and gravel for refugia. The tadpoles transform in 3 to 4 months, typically from July to October as newly metamorphosed juveniles migrate upstream from the hatching site. 

We at Sequoia look forward to working more with this newly listed species in an effort to protect and conserve what populations are left. Several of our hardworking biologists have the California Department of Fish and Wildlife’s permission to handle all life history stages of FYLF under Sequoia senior biologist Brett Hanshew’s MOU (memorandum of understanding). 

Stay tuned to learn more about the amazing species we work with at Sequoia! 

Deadly ‘Snake Fungal Disease’ Hits California

We are fortunate to work with many incredible species of snakes on a regular basis. Our native snake species occupy vital ecological niches within their broader environment. More specifically, these serpents serve to maintain a balanced food web as both prolific predators, and important prey for the likes of raptors and other elite hunters. From a human-centric perspective, the presence of healthy snake populations serves to keep rodents and other pests at bay.

Many of these rodent species can serve as vectors for zoonotic illnesses, such as the potentially deadly hantavirus in deer mice (Peromyscus maniculatus), or Leptospira bacteria in Norway/brown rats (Rattus norvegicus). Snakes predation also fuels natural pest control solutions in our agricultural fields. Considering this context, snakes are extremely beneficial to public health, and the health of our ecosystems and food webs at large.

In addition to rampant habitat loss and human encroachment, the state’s hard-working scaled critters now face a new threat: a deadly disease has officially been detected in Amador County, California. Snake fungal disease (SFD), Ophidiomyces ophiodiicola, is caused by a soil-borne fungus. This ailment causes facial abnormalities, scabbing, abnormal shedding, and other issues in several different species. Cases of infection range from mild to deadly as it consumes the keratin in the snake’s scales, often leading to the snake becoming emaciated.

The presence of the disease in California was discovered in late 2019 when a member of the public observed a California kingsnake (Lampropeltis californiae) in Plymouth, Amador County. The snake was emaciated and suffering from an apparent skin disease. The California Department of Fish and Wildlife (CDFW) euthanized the ailing serpent, which was later diagnosed with SFD at the University of Illinois, and began investigating. The fungus was later detected on the skin and in the tissues of an invasive Florida watersnake (Nerodia fasciata pictiventris) found in Folsom, Sacramento County. This bleak discovery suggests that the original case was not isolated.

The Ophidiomyces ophiodiicola fungus resides in soil and can infect snakes through skin abrasions or through direct contact with other infected snakes. The majority of our native snake species are fossorial (species which spend extensive time in subterranean dens and burrows), thus, native species such as the federally listed Alameda whipsnake (Masticophis lateralis euryxanthus), California kingsnake, and rubber boa (Charina bottae) could be quite susceptible to this infection should it spread.

Luckily, there are no known cases in Alameda whipsnake to this point, however, the implications for AWS are alarming if this infection does indeed spread over the state. In other parts of the United States, SFD has caused significant mortalities in species of conservation concern, such as the timber rattlesnake (Crotalus horridus) and federally threatened eastern massasauga (Sistrurus catenatus).

A Timber rattlesnake exhibiting early symptoms of SFD infection. Image: CBC Radio

Going forward, CDFW will be working with wildlife rehabilitators, academic and agency partners, and others who work with snakes to increase surveillance for SFD in California and implement appropriate precautions to minimize risk for human-caused spread among snakes (for example, spreading spores on the bottom of a boot). If you see any snakes exhibiting skin sores or unusual behaviors, report your sighting to CDFW to help track this disease.

At Sequoia Ecological Consulting, we do our best to uphold strict decontamination protocols before hitting the field. We will be following this development closely and working in conjunction with other agencies to report any sightings of snakes showing signs of SFD.


Snake Fungal Disease Detected in California. November 5th, 2019. California Department of Fish and Wildlife. CDFW News. Accessed at: https://cdfgnews.wordpress.com/2019/11/05/snake-fungal-disease-detected-in-california/

Lightning Storms and Wildfire Regimes in California

The Bay Area experienced a rare weather phenomenon last weekend (August 16th, 2020) when a summer lightning storm roared overhead in the midst of a blistering heatwave. The atypical weather was a result of the tropical storm Fausto off the coast of Baja California funneling moisture up into California. It was dangerously hot across the region on August 16th, as several cities logged record-shattering temperatures: for instance, Santa Cruz saw a high temperature of 107F which handily toppled the previous record high of 97F in 1983.

In addition to the heat, the Bay Area skyline erupted in a violent display of lightning and thunder. This combination, though beautiful, is especially dangerous for the drought-stricken state which has been plagued by devastating wildfires in recent years. According to Cal Fire, six of the ten most destructive California wildfires in recorded history have occurred over the past three years alone.

Many of these fires were the result of human activity, resulting from things like faulty infrastructure, but this recent summer lightning storm serves as a sobering reminder that mother nature reserves the ability to spark inferno as well as natural wildfire is a critical part of our state’s ecology. In the first 24 hours following the storm, nearly 1,600 lightning strikes and at least 76 corresponding wildfires were reported in northern California (Cal Fire). Many of these fires are still ablaze at the time of writing this post and are causing residents to evacuate their homes amidst the devastation.

Wildfire has always been a vital component of the state’s ecology. Often referred to as the “pyrostate,” California features a Mediterranean-type climate where summers are warm and dry and ignition in the presence of flammable biomass often leads to wildfire. As a result of these conditions, many of our ecosystems have close ecological and evolutionary associations with fire. These relationships vary substantially depending on factors such as the species involved, microclimates, and geography.

Historically, our lower elevation ecosystems (such as chaparral and shrubland) burned naturally at intervals of 100 to 130 years while the conifer forests of the high sierra are adapted to burn every 10 to 20 years. When human settlement and fire suppression disrupts these natural fire regimes, a surplus of fuels is created which makes storm events like what we experienced last weekend extremely volatile and dangerous.

Here at Sequoia Ecological we often work on projects which aim to manage fire danger through fuels management. These projects often aim to remove the excessive biomass which natural fire regimes would have kept in check prior to human settlement in the region. It is an honor to provide biological support for these wildfire mitigation projects which aim to lower fire danger in a warming climate.

California Bark Beetles, Wildfire, and the Intersectionality of Art and Science

Bark beetles are a highly diverse subfamily of weevils that spend most of their life histories within specific host plants. Native bark beetles typically play key roles in the structure of natural plant communities and large-scale biomes. In most cases, bark beetles infest their host plant to shelter from predation, feed and reproduce. In the event of a successful invasion, these beetles nearly always kill their host tree regardless of attempted human intervention (USDA, 2015).

During periods of balanced populations, trees killed by bark beetles provide essential habitat for a myriad of other organisms; however, as climate change results in warming and increased drought in certain regions, bark beetle populations have exploded in magnitude leading to the largest-scale tree mortality ever recorded from an insect infestation on multiple wooded continents (Mikkelson et al., 2013).

In the period between 2010 and 2017, an estimated 129 million trees succumbed to bark beetle infestation in California alone (Alexander, 2017). These dead trees become prime fuel for fire; in 2017 alone, 1.2 million acres of land burned in California wildfires. 

Bark beetles are cylindrical in shape with short legs, antennae, and stout mandibles for chewing through fibrous tree material. In California, the prominent native species are the mountain pine beetle, the fir engraver beetle, the western pine beetle, the Jeffrey pine beetle, and the pine engraver beetle. Although these beetles are indeed native, their life cycle activities can cause high levels of tree mortality state-wide (USDA, 2015).

Once a juvenile bark beetle finds a suitable new host, typically a specific species of tree, it finds an entry point and chews its way in. It is at this moment that a battle begins between the tree and the beetle. To combat the invaders, coniferous resinous trees produce a cocktail of chemical defenses called resin. The resin serves as a physical barrier, quite literally pushing the beetle out of the open wound. At times, the resin can even entomb and kill the beetles.

So, with these natural defenses built into our trees, why are bark beetles wreaking havoc on California forests? There is the rub: bark beetles face very little resistance when attacking a previously stressed tree. Tree stress can be caused by construction, paving, excavating, wind, lightning, and most importantly: drought. Climate change has led to an increase in the severity of droughts in dry areas worldwide (Raffa, 2015).

In California, the period between 2011 and 2015 marks the driest since record-keeping began in 1895 (Hanak, 2016). During extreme drought conditions, water-stressed coniferous resinous trees often fail to produce enough resin to successfully fight off invading beetles (Roth, 2015). Without the critical chemical defenses to slow them down, bark beetles can easily decimate vast numbers of drought-stressed trees.

Beetles are also able to expand their range to higher latitudes and elevations with rising global average temperatures, infiltrating forests that have not evolved natural defenses (Mikkelson, 2013).  Interestingly, in early 2020, a joint study conducted by the National Park Service and the U.S. Geological Survey showed that bark beetle infestation was partially responsible for the deaths of more than two dozen giant sequoia trees in Sequoia and  Kings Canyon national parks.

These trees are known to live up to 3,000 years and usually only die when they become too big to support their own weight. The study into why these iconic trees are just now succumbing to bark beetle infestations for the first time is ongoing, however, drought stress and rising temperatures are the leading suspects. 

Perhaps all is not lost to the beetles, however. One innovative UCSC music professor has developed an unlikely potential solution to combat our bark beetle problem. For well over a decade, Professor David Dunn has created music using the sounds of nature, specifically recordings of bark beetles chewing on California’s trees. He now holds a patent for a unique device that uses sound (which he refers to as his “chaotic oscillators”) as a targeted sonic weapon to disrupt the feeding, communication, reproduction, and various other essential behaviors of bark beetles when it is played into an invested tree.

Professor Dunn combined the sounds of beetles with randomly generated electronic sounds which confuse the beetles and halt their basic functions. When played long enough, the beetles are rendered sterile and can even become cannibalistic, eventually wiping out the entire population inhabiting the treated tree. The beetles are not able to get used to and adjust to the sounds, as the chaotic oscillators never repeat themselves, the randomly generated sounds are patternless. Professor Dunn states:

“We have now entered into a period of common interests between art and science largely driven by the commonality of digital tools.

Artists are now just as involved in designing such tools as the scientific community, and often create software and instrumentation in order to facilitate their creative visions that may ultimately be of even greater value to scientific research. I think that this was one of those instances and a couple of fortuitous events conspired to allow something interesting to happen.”

Professor Dunn is currently working with his research group to digitize his analog circuitry and research ways to effectively deploy the sonic tool into forests at a large scale.


Alexander, Kurtis (2017). California Losing 2 Million Trees a Month as Drought-Related Plague Drags On. SF Gate. Retrieved from: http://www.sfgate.com/science/article/Drought-related-tree-die-off-continues-to-plague-12422751.php

Hanak, Ellen et al. (2016). California’s Latest Drought. Public Policy Institute of California. Retrieved from: http://www.ppic.org/publication/californias-latest-drought/

Mikkelson, Kristin et al. (2013). Bark Beetle Infestation Impacts on Nutrient Cycling, Water Quality and Interdependent Hydrological Effects. Biogeochemistry 115. Doi: 10.1007/s10533-013-9875-8

Raffa, Kenneth et al. (2015). Bark Beetles: Biology and Ecology of Native and Invasive Species. San Diego, CA. Academic Press Roth, Sammy. (2015).

Dying California Trees Raise Wildfire Risk. USA Today. Retrieved from: https://www.usatoday.com/story/news/2015/05/15/california-drought-trees-wildfire-bark-beetles/27400801/

United States Department of Agriculture. (2015). Bark Beetles in California Conifers: Are Your Trees Susceptible? (R5-PR-003). United States Government Publishing Office.