Science Spotlight

USFWS Photo by Brett Billings


Figure 1 from The Xerces Society’s Conservation Status and Ecology of the Monarch Butterfly in the United States (PDF)

For residents of many coastal California towns, the colorful Monarch butterfly (Danaus plexippus plexippus) migration has been a welcome wintertime sight for generations. The beautiful and distinctive orange-and-black patterned insects have historically congregated at more than 400 known sites in the Golden State. Visitors flock to see them, and some towns – such as Pacific Grove, Big Sur and Pismo Beach -- have built entire economies around the return of the butterflies.

The life history of the Monarch butterfly is fascinating in that none of the individuals that arrive each winter have ever been there before. Each year, the Monarchs that were born throughout western North America flutter to the warmer climates of the California coast, typically in mid-October, but sometimes as early as September. They form dense masses high in the trees, where they remain relatively dormant (scientifically known as reproductive diapause) until February or March, when flowers with nectar and the milkweed needed by their young (caterpillars) become plentiful. At that time, they mate and begin to disperse and lay their eggs. The offspring then grow into butterflies, which in turn mate and lay eggs while continuing to disperse over a two to five week period. The process continues until fall when temperatures drop, triggering migration of the current generation of butterflies back to the west coast.

As recently as the 1990s, an estimated 1 million butterflies would overwinter along the California coast each year. But over the past several decades, that figure has rapidly plummeted. Recently, the Xerces Society, an international nonprofit focused on the conservation of invertebrates and their habitats, released the results of its Western Monarch Thanksgiving Count, and the news is dire – just 28,429 overwintering Monarchs were counted in California, which is an 86 percent decrease from the count at the same time the previous year.

Washington, Oregon, Idaho, Utah, Nevada and Arizona are seeing similar drops in numbers during the breeding season.

“In addition to fewer monarchs, we’re losing the phenomenon of the migratory behavior,” explains Karen Miner, chief of CDFW’s Biogeographic Data Branch. Miner serves as the chair of the Western Monarch Working Group, a task force consisting of biologists from the seven state agencies. The biologists have been working with experts for months to identify possible causes of the decline, as well as actions that could be undertaken to encourage Monarch population growth.

Unfortunately, there are no easy answers, or easy solutions. According to the Xerces Society report, “the factors that influence Monarch population dynamics in the Western U.S. are still not completely understood.”

In California, some specific factors contributing to the decline of the Monarchs include:

• Loss of overwintering habitat along the coast. Favorable weather conditions along the California coast attract people as well as the butterflies, and urban development has removed or crowded many of the sites traditionally used by monarchs in the winter. Many of these sites feature eucalyptus trees, originally introduced from Australia in the 1800s. These towering giants historically provided shelter to overwintering Monarchs. But now, the trees are dying of old age as well as the effects of recent drought conditions and disease. Nectaring plants that provide food for overwintering butterflies are also becoming scarce. Protecting and restoring these coastal sites to meet the needs of wintering Monarchs is a top conservation need.
• The loss of native milkweeds and flowering plants, particularly in the areas where the first eggs would be laid in the spring. Milkweed is a Monarch staple. Butterflies lay their eggs on it, and the emerging caterpillars use it as a food source. Adult butterflies rely on flower nectar for their source of food. As with overwintering habitat, development and land management practices have reduced the amount of milkweed and nectar sources available for Monarchs and other pollinators. Many nurseries and hardware stores sell milkweed, which seems like a Monarch-friendly practice on the surface. But much of the milkweed that’s commercially available to gardeners is non-native, and scientists have noticed that the butterflies attracted to it are more prone to disease, and less likely to migrate to overwintering sites.
• Complications of a changing climate. Based on annual counts at overwintering sites, the Monarchs that do overwinter are arriving later and leaving earlier. Scientists are concerned that food resources and milkweed for egg laying are not yet available for the Monarchs when they need it. CDFW urges the public to report sightings of Monarchs and the plants they are feeding on to Western Monarch Milkweed Mapper. This tool, which also allows citizen scientists to upload photos, will help biologists better understand the distribution and life cycle of both the butterflies and their host plants.

“Can we reverse this? It’s a complicated issue, and it’s going to be hard,” Miner says. “We need to take a number of different approaches. We have to protect overwintering groves, educate the landowners and neighbors of these sites, and we need to improve pollinator habitat including milkweed availability. Each state in the west has a role to play, and so many people can contribute to this effort – citizen scientists, educators, garden club members, agricultural growers, and rights-of-way managers such as utilities or transportation agencies.”

The US Fish and Wildlife Service is currently reviewing a petition to list the monarch under the Endangered Species Act, but the member states of the Monarch Working Group are wasting no time in moving forward with their own efforts to conserve the butterflies. At a meeting of the Western Association of Fish and Wildlife Agencies in January, the group finalized its Western Monarch Butterfly Conservation Plan (PDF), which establishes population size and habitat conservation goals, strategies and specific actions. Specific goals include creating an additional 50,000 acres of Monarch-friendly habitat in the Central Valley and foothills, establishing protection and management for half of all currently known overwintering sites, and, ultimately, achieving an average count of 500,000 overwintering butterflies in the west by 2029.

Photos courtesy of USFWS and Xerces Society. Top Photo: USFWS Photo by Ryan Hagerty

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Media Contact: 
Kirsten Macintyre, CDFW Communications, (916) 322-8988
Kyle Orr, CDFW Communications, (916) 322-8958

David Wright uses a mirror to reflect light into dark rock crevices in search of pika sign such as scat or urine stains. CDFW image by Joseph Stewart.


Joseph Stewart hikes through one of the mountainous locations in the northern Sierra Nevada that researchers searched for habitat that appeared suitable for pikas. CDFW image by Johanne Boulat.

CDFW staff recently conducted a study to determine whether American pika in California are able to find sufficient refuge from elevated temperatures in their natural habitat. Previous CDFW collaborative research and related work has suggested that pikas in California and Nevada have been declining in warmer areas, but some scientists contend that underground temperature refuges will protect pikas from warming temperature trends.

“The question of whether pikas are protected or exposed to warming temperatures seemed key to us,” said David Wright, a retired CDFW senior environmental scientist who co-authored the research with Joseph Stewart, a former CDFW scientific aid and now a University of California, Davis post-doctoral researcher. “It is central to whether or not climate change is going to push pikas to higher, cooler elevations and significantly reduce and fragment their range, in our state, on our watch.”

Pikas are small herbivores related to rabbits that live in fields of broken rock (talus) in the mountains of western North America. Researchers examined 46 mountainous locations in the northern Sierra Nevada with habitat that appeared suitable for pikas.  

Pikas prefer talus with rocks eight inches to three feet in size, and larger or less isolated talus fields are generally more likely to support pikas.

“We did our research at elevations both within and below the expected elevation range of pikas,” Wright said. “Lower elevations on average have warmer temperatures, which pikas don't tolerate well, but it's been suggested that talus provides a refuge from warmer temperatures. We wanted to look at this hypothesis.”

Two species of pika occur in North America, with only the American pika found within the continental U.S. With their high metabolic rates and thick fur (including inside their ears and on the bottoms of their feet), American pikas are well adapted to cold temperatures at high elevations. They do not hibernate during the winter, and spend the summer gathering grasses and wildflowers to store in “haypiles” for subsistence during the winter. Hikers may know them from their distinctive alarm call, a high-pitched cross between a chirp and a bark.

In 2010 to 2013, using small, year-round temperature recorders lowered approximately 1.6 feet to 3.3 feet into talus, along with visual surveys for pikas or signs of pikas, Wright and Stewart found that temperatures below the talus surface were buffered from warm and cold extremes of ambient air temperature. This was consistent with previous findings.

However, pikas were not found wherever talus temperatures were suitable. Temperatures within talus were mostly suitable for pikas across all the study sites regardless of elevation, yet pikas were absent from many of the sites. Instead, summer air temperatures proved to be the best predictor of pika presence or absence. The warmest sites had no evidence of pikas, followed by warm sites that had only remnant fecal pellets (pika pellets can persist among the rocks for decades), then slightly cooler sites that supported pikas in some years but not in others, to the coolest sites which supported persistent populations of pikas throughout the study.

“It’s not enough to have suitable temperatures in their underground burrows,” said Stewart. “Pikas also need suitable temperatures above ground where they forage for food.”

The authors concluded, based on their own and other research, that daily warm air temperatures may inhibit pika foraging and survival because they cannot tolerate the heat, and juvenile survival and dispersal may be similarly impaired by elevated summer high temperatures. Talus provides a cool refuge for pikas up to a point, but beyond that point pikas still need to forage and complete the portions of their life cycle that occur aboveground. This balance point, from this research, appears to be near an average warm season (June to September) air temperature of 71 to 73 degrees.

Funding for this research and similar CDFW efforts in the Sierra Nevada are supported by State Wildlife Grants administered through the U.S. Fish and Wildlife Service.

The study, Within-talus temperatures are not limiting for pikas in the northern Sierra Nevada, California, USA, can be viewed here (PDF).

CDFW Photos. Top Photo: Pikas are small herbivores that live in fields of broken rock (talus) in the mountains of western North America. CDFW image by Jan Dawson.

Media Contact:
Kyle Orr, CDFW Communications, (916) 322-8958

The latest two issues of California Fish and Game, CDFW’s long-running scientific journal, are now available online.

Issue 104(3) features a rather dignified-looking desert spiny lizard (Sceloporus magister) on the cover. It is one of 15 species captured and documented by Cummings et. al in Biodiversity of amphibians and reptiles at the Camp Cady Wildlife Area, Mojave Desert, California and comparison with other desert locations. The paper’s eight authors spent months in the Mojave desert location, trapping and identifying its inhabitants. The finding were combined with a review of scientific literature to document the biological diversity of the area in comparison to other desert habitats.

Also in Issue 104(3):

• Annual and seasonal variation, relative abundance, and effects of managed flows on timing of migration in Brown Trout (Salmo trutta) in the upper Trinity River, by Sullivan and Hilemen, challenges a previous study suggesting that brown trout populations are increasing in the upper Trinity River and are having a negative impact on native juvenile anadromous salmonids. The authors assert that previous trapping data suggest a behavioral response to managed flow regimes rather than an increasing population. Further, they provide management recommendations to determine whether the removal of brown trout—an important economic sport fishery resource—is necessary and has the potential to be successful.
• Geographic range and biology of Spinyeye Rockfish (Sebastes spinorbis Chen, 1975), an endemic species to the Gulf of California, Mexico, by Acevedo-Cervantes et. al. The authors add to the existing knowledge of a marine species that is currently not a fishing target and about which little is known.

Issue 104(4)’s cover photo illustrates the article Ground-nesting great horned owl in Suisun Marsh, California. Skalos et. al provide vivid descriptions and photographs of great horned owl nest sites, ranging from non-native eucalyptus trees to man-made structures (such as the dock piling shown in the cover photo) and even ground nests. Though great horned owl nest sites are known to be diverse, little documentation exists to support some of these observations. In fact, Skalos et. al’s ground nest observation is the first documented case in California.

Also in Issue 104(4):

• Prey of neonate leopards Sharks in San Francisco Bay, California by R. Russo. The leopard shark has been the focus of several studies documenting the diet of juvenile through adult stage animals. The author examined the stomach contents of neonate leopard sharks and found that small, easily accessible prey items such as bay shrimps and polychaete worms are important for rapid growth of leopard sharks during the first year of life.
• Within-Talus temperatures are not limiting for pikas in the Northern Sierra Nevada, by Wright and Stewart. Pikas are small herbivores related to rabbits that live in fields of broken rock (talus) in the mountains of western North America. Researchers examined potentially suitable talus habitats at various elevations in the northern Sierra Nevada. Their findings suggest that the cooler temperatures provided by talus is not sufficient to sustain pikas. The aboveground air and surface temperatures, rather than temperatures within talus, pose a greater challenge to pika survival.

California Fish and Game provides important contributions to the existing body of scientific knowledge. First published in 1914, California Fish and Game is the longest continuously published scientific journal. For more information and other back issues, please visit CDFW’s website.

CDFW Photos.

Media Contact:
Lorna Bernard, CDFW Communications, (916) 322-8911

Circling birds indicate an offshore herring spawning event near Alameda.


Bird activity after a spawning event.


Heavy spawn on eelgrass.

On a drizzly winter day in San Francisco Bay, you might find CDFW Environmental Scientist Ryan Bartling surveying the shoreline on the research vessel Smoothhound in search of Pacific Herring (Clupea pallasii) eggs. Bartling is one member of a team of state biologists who monitor the San Francisco Bay Herring fishery in the winter months, counting eggs and using those numbers to estimate the size of the Herring population that enters the Bay each season. CDFW Environmental Scientists Tom Greiner and Andrew Weltz are the other members of the Herring Team who lead the collection of biological data and management of commercial take of Herring in San Francisco Bay.

“We see, on average, about 50,000 tons of Herring come into San Francisco Bay during the spawn events that occur about 12 times each year,” Bartling explains. “The fish typically show up from November through March, so that’s when we’re out there counting eggs and collecting biological information on adult Herring.”

Even before the spawning season starts, Bartling and Weltz, with assistance from other CDFW divers, perform SCUBA surveys in the Bay to estimate how much vegetation is present. In-season, Greiner runs weekly trawl surveys, using the 28-foot research vessel Triakis to catch adult Herring before they spawn. This catch provides information on size, weight and age of the adult herring, it also provides information on general health and condition.

Once the spawning begins, the biologists concentrate on spawn deposition surveys – which involves finding and counting egg masses wherever the fish lay them. Eelgrass (Zostera marina) and red algae (Gracilaria species) are common vegetation types for spawning Herring, but the fish will also gravitate to hard surfaces or man-made structures near the shoreline – pier pilings, boat bottoms and even submerged shopping carts, anything in the vicinity of a spawn is fair game. Although the eggs are tiny (about the size of the tip of a pencil), they’re laid in mass.

How do the biologists know where to look? There’s a dead giveaway. “The key indicators are the birds and marine mammals – they always find them first!” Bartling says. Using the circling birds as his guide, Bartling walks along the shoreline at low tide to do a visual count of eggs, or, if aboard the Smoothhound, he uses a rake to pull up vegetation from below.

When a spawning event is occurring, the actual survey time varies. CDFW scientists could be counting eggs for as little as four hours, or as long as 12 hours at a time depending on the size of the Herring school. Using the egg count numbers (which are typically in the billions or trillions), they can calculate estimates of Herring tonnage. “An estimate could be as small as one ton of Herring per spawn event up, or might be as high as 15,000 tons,” Bartling says. “It depends on time of year and the overall stock size.”

The estimates are necessary for CDFW to set quotas for California’s commercial Herring fishery, which runs from January through mid-March. Quotas are typically set at around 5 percent of the total tonnage the biologists calculated from the previous season.

CDFW Herring fishery management staff maintain a blog, CDFW Pacific Herring Management News, to keep the public apprised of the health and status of the fishery. More information about the commercial Pacific Herring fishery can be found on CDFW’s website.

CDFW Photos. Top Photo: CDFW Environmental Scientist Ryan Bartling looks at herring eggs after a spawning event.

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Media Contact:
Kirsten Macintyre, CDFW Communications, (916) 322-8988

At Iron Gate Hatchery in Hornbrook, the fall 2018 spawning operation has just concluded. Iron Gate spawns both Fall-Run Chinook Salmon and Coho Salmon from the Klamath River. For Chinook, the hatchery staff manually collect the eggs and mix it with the milt immediately after the fish come into the facility. CDFW environmental scientists also collect heads from adipose fin clipped salmon, in order to retrieve implanted tags in the snout. The retrieved tags tell the biologists which hatchery the fish is from, and when it was released. They also collect scales, which enable them to determine the age of the fish.

For Coho Salmon, the process is a little more involved. The Coho are measured and samples taken, but the samples are sent off to a National Oceanic and Atmospheric Administration (NOAA) laboratory in Santa Cruz for analysis. While the samples are processing, the fish are kept in individually-numbered holding tubes at the hatchery. They will be spawned after the tissue analysis determines which fish are the best genetic match.

CDFW Photos

For more information about Iron Gate Hatchery, please visit: www.wildlife.ca.gov/Fishing/Hatcheries/Iron-Gate.

Media Contact:
Kirsten Macintyre, CDFW Communications, (916) 322-8988