Frog Nanny


Tending to tadpoles means carefully monitoring water quality and providing a constant supply of food.

Frog nanny is not an official job title, but it’s been my reality this year. I’m the “nanny” for some 1,176 healthy mountain yellow-legged frog (MYLF) tadpoles.  This iconic California species is one of the most endangered frogs in North America. San Diego Zoo Global has been involved in the MYLF recovery program since 2009, and captive breeding has been an important component of our efforts to re-introduce froglets into their natural habitat in the Sierra Mountains. However, with little information on MYLF life history, the care and reproduction of these frogs in captivity presents many challenges.

I have been working on this project full-time since last October. As I enter the lab and look into the 100-gallon containers holding the result of this years’ extremely productive breeding season, a feeling of excitement and nervousness comes over me. It takes about a month and a half for MYLF embryos to hatch out into free-swimming tadpoles, and in the meantime, they require daily preening. Early in the breeding season, I start my day by counting and cataloging over 1,800 embryos. Something like picking ticks off a chimpanzee, this entails cutting through the surrounding egg jelly and extracting any unfertilized or dead embryos from neighboring healthy ones. Sitting at the dissecting microscope, I examine and record what stage of development each embryo has reached every day. By the afternoon, I am all but cross-eyed. I walk around with constant images of beautifully formed black spheres in my mind’s eye. As the embryos grow and thrive, the stress of getting them through the early stage of development is taken over by concerns for stage two of tadpole rearing.


These black specks are mountain yellow-legged frog embryos.

So what is stage two? We begin by focusing on what tadpoles need. MYLF tadpoles require cold, clean water, constant feeding, and plenty of space to grow. Like most infants, tadpoles are voracious eaters and require a constant supply of food. If too much food is offered, it accumulates in the tank, causing water quality issues. Too little food, and big brother Jake might start nibbling on his smaller sibling Fred. Cannibalism is not uncommon in amphibian species, so all I can do to stop Jake from eating his brothers and sisters is make sure I feed him enough.

Amphibian nutrition is a work in progress, and little is known of individual species’ requirements. This year, I have gone from reproductive physiologist to dietician. Researching amphibian nutrition is complicated by the specific needs of each life stage. Luckily, I have a supporting team of professional nutritionists and a wealth of knowledge and years of experience, courtesy of Brett Baldwin and David Grubaugh, amphibian/reptile keepers at the Zoo.

Controlling water quality is another daily necessity. The difference between clean and pristine can be subtle, and can affect growth and development in ways that may not be apparent until it is too late (like during metamorphosis). Armed with the HACH colorimeter DR-900, a small team of us (Nicole Gardner, senior research associate; Bryan King, research associate; me; and our weekly volunteers, Jaia Kaelberer, Janice Hale, and Jim Marsh) conduct daily screenings of the water in which our tadpoles live. Based on data we have collected on the water quality in MYLF habitat, we have specific parameters to which we can set our water standards in the lab.


Helping to raise new generations of mountain yellow-legged frogs is challenging, but rewarding.

They say “be careful what you wish for.” This year, we wished for a handful of MYLF egg clutches to be laid and for a couple of hundred embryos to survive. Instead, we got almost 2,000 eggs! As they grow, we become faced with a new challenge—overcrowding. To my relief, the solution becomes clear; together with our partners at the US Geological Survey and the Department of Fish and Wildlife, we decide to split our bountiful cohort of tadpoles into smaller groups. At the end of May, 711 lucky tadpoles made their triumphant way back to the wild, and 400 of their brothers and sisters stayed here with us. They will be “headstarted” and returned to the wild as froglets.

Everyone involved in this project lives and loves every moment. There is nothing more satisfying than watching a life form grow and thrive under your care. This year’s breeding season has exceeded all our expectations. If we take into account that less than one percent of MYLF tadpoles are estimated to survive to metamorphosis and only an estimated 200 adults remain in the wild, everyone currently involved in this project holds the key to this species’ survival. That can be stressful, but it is also a humbling honor. I am happy to speculate that this is going to be a good year for our MYLF program, and that I will have the chance to be part of their journey back to nature.

Natalie Calatayud is a research associate at the San Diego Zoo Institute for Conservation Research. Read her previous blog, Rocky Mountain High: Boreal Toads Going to a Place They’ve Never Been Before.


Hungry New Insectivores in Town

Researcher Frank Santana prepares to release his charges into a mountain stream.

Researcher Frank Santana prepares to release his charges into a mountain stream.

The little dotted frogs could not have picked a more picture-perfect day for their release into a remote mountain stream within their historic habitat. As wind rustles the swaying tree crowns and sunshine warms our backs, the team of multi-agency collaborators—along with a bevy of reporters—descends on Indian Creek in the San Jacinto Mountains. Bred at the San Diego Zoo Institute for Conservation Research, 65 juvenile mountain yellow-legged frogs Rana muscosa are stowed in pairs in Tupperware containers (with puncture holes) in 2 large, temperature-controlled coolers, awaiting their freedom…and a feast of fresh crickets skirting over the water’s surface. It’s an exciting milestone, years in the making.

Amphibian Adventure
In 2002, the U.S. Fish and Wildlife Service listed Southern California’s mountain yellow-legged frog (MYLF) as endangered, with fewer than 200 adult frogs scattered throughout perennial streams in the San Gabriel, San Bernardino, and San Jacinto mountains. In 2006, a group of tadpoles (once referred to as pollywogs) were collected from the wild and brought to the Zoo’s Institute for Conservation Research. Research Coordinator Frank Santana took painstaking care of little guys, monitoring tank temperature, water quality, ambient light, and everything that could possibly impact the froglets’ development.

Though there was high survivorship, breeding seemed to be at an impasse, so Frank came up with an experiment to let a subset of the frogs hibernate for 60 days in a wine chiller. This proved to be the answer to the amphibian amour riddle, as the hibernated individuals were soon mating after “waking,” with six clutches of eggs laid within two days. With the fertility issue solved, Frank was able to shift his focus to field reintroduction efforts, which culminated in the dozen people buzzing about the three release sites in the stream on June 12, 2013. By raising the tadpoles in captivity into their tailless juvenile stage (about 14 months), it is hoped that there will be less predation and higher survivorship of these animals in the wild. Driving up to the release site, Frank confides that these dappled frogs are “just as deserving of a CHP escort as the pandas.” Given the years of research and collaboration required to get to this MYLF release, I’d have to agree.

The radio telemetry "backpack" will enable researchers to keep tabs on the mountain yellow-legged frog for 30 days, when it will be removed.

The radio telemetry “backpack” will enable researchers to keep tabs on the mountain yellow-legged frog for 30 days, when it will be removed.

The Fungus Among Us
Mountain yellow-legged frogs have not graced this stream since the 1990s when the perfect storm of habitat loss and degradation, nonnative introduced trout, which eat the frogs and their eggs, and the deadly amphibian chytrid fungus sweeping the globe, conspired to destroy this species. It’s up to humans to repair MYLF habitat and safeguard against the chytrid fungus. As the road wound higher into the mountains, Frank shared with me the “extra step” taken to ensure these animals released have the best chance at survival. “We are soaking the frogs twice for 4 hours in water containing beneficial bacteria, to protect them against the chytrid fungus.” Dr. Vance T. Vredenburg, a professor at San Francisco State University, discovered that a naturally occurring strain of bacteria may help ward off the fungus in frogs. This could be a game changer for amphibian conservation!

Frank gently released 65 juvenile mountain yellow-legged frogs into the stream.

Frank gently released 65 juvenile mountain yellow-legged frogs into the stream.

Release Me
Frank and Adam Backlin from U.S. Geological Survey (USGS) crouch next to the stream with several Tupperware containers bobbing on the surface. Stream water seeps in through the air holes and the frogs seem giddy with their natural habitat so near. Other USGS staff is testing the tiny “backpacks” of radio transmitters, which will be strapped onto 15 of the frogs released. This will enable researchers to track the frogs for the next 30 days to see where they settle, and then remove the transmitters. Frank wades knee-deep into the creek and gently holds a spotted, two-inch long frog on his palm over the water. The frog pauses (for a photo?), then leaps into the water, diving deep into the blessed muck on the bottom. Frank scoops up another frog. Cameras click. The liberation process is mesmerizing. One frog hops back into his Tupperware, but quickly changes his mind. Splash! As we stand under the warm sun, the frogs begin to swim to the surface, eying their audience from their chilly element. They linger, as we do, savoring this giant leap for amphibian conservation.

THANK YOU! San Diego Zoo Global is grateful to mountain yellow-legged frog recovery collaborators at the Los Angeles Zoo, the U.S. Forest Service, U.S. Geological Survey, California Department of Fish and Game, and U.S. Fish and Wildlife Service.

Karyl Carmignani is a staff writer for San Diego Zoo Global. Read her previous post, Chillin’ Out with Cold-Blooded Creatures.


Facebook Winner Joins Us in the Field

From left to right: Facebook winner Jeff Williams, research technician Frank Santana, UC James Reserve Director Rebecca Fenwick

When we got to the gorgeous University of California James Reserve in the San Jacinto Mountains, the sun was high and the sky was a clear, deep blue. We lucked out. It was the perfect day to take our Facebook winner, Jeff Williams, with us into the field to take part in our mountain yellow-legged frog project. It was also apparent by the conversation we had in the two-hour car ride up to the mountains that Jeff was the perfect candidate to take with us.

An avid outdoorsman, Jeff’s passion for nature and the wildlife therein was palpable. It turned out that Jeff used to breed blue dart frogs, a hobby catalyzed by an encounter he had with wild frogs in Costa Rica. “I thought it was amazing to come across these fluorescent spots of light in the forest all around you,” he said. A love of wildlife also runs in Jeff’s family. After learning that meat came from animals at the age of four, his daughter chose to be vegetarian. “It’s kind of a good thing because it forces us to eat healthier,” Jeff said.

Jeff was also very interested in the project, and asked Frank Santana, our lead field technician, a million questions about mountain yellow-legged frogs (MYLF) and their plight. We learned that the chytrid fungus is the main reason for the frog’s alarmingly rapid decline. The fungus affects the keratin layer of skin and impairs the frogs’ ability to exchange oxygen and carbon dioxide through their skin, resulting in a slow suffocation. The species also faces threats from pollution and introduced predators like brown and rainbow trout. I also learned that historically there were 160 populations of MYLF in the region, now there are just 9. In fact, 33% of all amphibian species worldwide are threatened by extinction, with threats from habitat loss, pollution, introduced species, and chytrid. This knowledge gave our work renewed gravity and purpose in my mind.

When we broke off the beaten path toward the wild stream where we had released about 500 critically endangered mountain yellow-legged frog tadpoles earlier this year, it was clear that we were in for an adventure. Soon we were climbing over fallen logs, thrashing through dense foliage, and wading in knee-deep water. Our goal was to hike upstream in search of tadpoles that may have dispersed from their original release pools. Jeff didn’t get off easy. We put him to work searching for tadpoles and measuring the length, width, and depth of certain pools, and he gladly indulged us. He was an important part of the team for a day. He even brought some useful equipment with him, like a super-small, super-bright LED flashlight that really came in handy for searching dark pockets of water. In fact, many of the pictures we captured of tadpoles wouldn’t have come out without Jeff shining his flashlight in the water.

After a few hours of searching the stream we had yet to find tadpoles, even with the help of UC James Reserve Director Rebecca Fenwick. It wasn’t until we got to the most upstream release pool that we saw about five tadpoles, which believe it or not is a good sign, since tadpoles face threats from many predators in the wild. It was an incredible feeling to finally spot the little guys. “After all that work it’s good to see that they’re still there and hopefully they’ll start to see some success,” Jeff said. I think we can all agree.

It was an absolute pleasure having Jeff along with us. We appreciated his help and had an awesome time “doing science” with him. Like our facebook page for a chance to fill Jeff’s shoes and ride along with us into the field for our cactus wren project.

Matt Steele is the social media planner for San Diego Zoo Global. Read his previous post, Summer SCVNGR Safari.


Mountain Yellow-Legged Frogs: Life Beyond the City

The San Gabriel Mountains tower over the Los Angeles basin like sentinels. Heading up a winding highway into the mountain wilderness leaves all signs of the urban landscape behind. Stoplights, mini malls, and highways are replaced with trees, birds, and steep cliffs. Climbing further up the mountain reveals a wilderness teeming with amazing sights and a cacophony of sounds that stimulate the senses. Colorful butterflies, amazing wildflowers, and chirping frogs are all regular parts of the mountain landscape.

As a biologist with the San Diego Zoo Institute for Conservation Research, Southern California’s mountains are my office and outdoor laboratory. The goal of my research is to improve our understanding of the critically endangered mountain yellow-legged frog Rana muscosa with the ultimate goal of reintroducing poopulations back into the mountains of Southern California. Every summer for the last three years I have headed up into the mountains to learn as much as possible about these magnificent and beautiful frogs. One third of the world’s amphibians are in decline, and by focusing our research on the mountain yellow-legged frog, the San Diego Zoo is working to do our part to save frogs from extinction.

Scientists noticed that mountain yellow-legged frogs were experiencing severe declines in Southern California during the 1990s, and in 2001 they were listed as an endangered species under the Federal Endangered Species Act. The exact reason for the drastic declines are unclear, but we suspect that the deadly amphibian chytrid fungus may have played a major role in population declines. In addition, the species faces pressures from habitat loss, wildfires, water pollution, global warming, and introduced predators. Today only nine populations of mountain yellow-legged frogs exist in Southern California.

This summer I am focused on understanding the population demographics of wild mountain yellow-legged frog tadpoles. With the assistance of our summer research fellow Stephanie Wakeling, we are hoping to gain insight into the survival rates of tadpoles during their two to three years of life before they metamorphose into frogs. Keep an eye out for a regular series of blog entries as we share this exciting research with you throughout the summer.

Frank Santana is a research technician at the San Diego Zoo Institute for Conservation Research. Read his previous post, Desert Memories.