San Diego Zoo Institute for Conservation Research


San Diego Zoo Global Researchers Tackle Reproductive Challenges in Southern White Rhinos


Two  female southern white rhinos enjoy a new grass-based pellet as part of their morning meal at the San Diego Zoo Safari Park.

The reproductive physiology team at the San Diego Zoo Institute for Conservation Research has been working for seven years to determine why southern white rhino females born in zoos tend not to bear offspring as often as their wild relatives. It was recently discovered that the animals may be sensitive to compounds called phytoestrogens found in soy and alfalfa, which are a component of the animals’ diets in zoos.

“During their 16-month gestation, female calves could be exposed to the compounds through their mother’s diet, resulting in permanent infertility issues later in their life,” explained Christopher Tubbs, Ph.D., a scientist in the Reproductive Physiology Division of the San Diego Zoo Institute for Conservation Research. “Through our studies, we have found these plant-based phytoestrogens activate receptors that regulate estrogen function.”

Only about one-third of southern white rhinos in zoos successfully reproduce in their lifetime, making a sustainable population a challenge. This problem is not found in other species of rhinos living in zoos. To find a solution to this complex reproductive problem, Tubbs and his colleagues have spent extensive time in the lab, testing the diets of southern white rhino females at the San Diego Zoo Safari Park, as well as those of female southern white rhinos from eight other zoological facilities in the U.S. Many of these diets were found to be high in phytoestrogens.

On the basis of Tubbs’ findings, Michael Schlegel, Ph.D., director of Nutritional Services at San Diego Zoo Global, recently developed a grass-based pellet for rhinos that is low in phytoestrogens. “Besides formulating the pellets that are low in phytoestrogens, we also are ensuring the pellets are supplying concentrations of nutrients that will support reproduction,” stated Schlegel. The pellets are currently being fed to the southern white rhinos at the Safari Park, with the hope that the lower phytoestrogen content will help solve this reproductive issue. Further diet studies will continue, including research on how phytoestrogens are metabolized in the rhino gut. While the reproduction of white rhinos in zoos is still uncertain, the development and implementation of new science-based efforts could be beneficial to the conservation of white rhinos in the future.

The project has reached a real point of urgency, due to the increase in poaching in recent years that has dramatically affected rhino populations in the wild. “When I started this project in 2007, 13 rhinos were poached (that year),” stated Tubbs. “Last year, more than 1,200 southern white rhinos were poached in South Africa—one every eight hours. More than ever, we need a self-sustaining population of white rhinos established outside of Africa.”

Rhinos are poached for their horn, which is made of keratin—the same material that forms human fingernails. Rhino horn has been erroneously thought to have medicinal value and is used in traditional remedies in some Asian cultures. In addition, objects made of rhino horn have more recently become a “status symbol,” purchased to display someone’s success and wealth, because the rhino is now so rare and endangered.

Bringing species back from the brink of extinction is the goal of San Diego Zoo Global. As a leader in conservation, the work of San Diego Zoo Global includes on-site wildlife conservation efforts (representing both plants and animals) at the San Diego Zoo, San Diego Zoo Safari Park, and San Diego Zoo Institute for Conservation Research, as well as international field programs on six continents. The work of these entities is inspiring children through the San Diego Zoo Kids network, reaching out through the Internet and in children’s hospitals nationwide. The work of San Diego Zoo Global is made possible by the San Diego Zoo Global Wildlife Conservancy and is supported in part by the Foundation of San Diego Zoo Global.

Photo taken on Sept. 29, 2015 by Tammy Spratt, San Diego Zoo Safari Park.


Observing Behavior in the Wild


One of our camera traps caught this deer mouse heading for a burrow.

My favorite part of the fieldwork I do (see: A Night with the Pocket Mouse Field Crew)  is watching the pocket mice, kangaroo rats, and other small mammals in the wild. I love releasing them from a trap and watching them take a sand bath, or dig up a cache of seeds they buried previously, or sometimes dive into the closest burrow and get chased right back out by its owner who was already inside.

While the reward (and often the data!) of an animal behavior study is observing your subject do what it does, figuring out how to make the observation can be one of the biggest challenges. You don’t want your presence to affect what the animal is doing—unless you are observing their response to humans.

With big animals that live in fairly open environments, sometimes you just need to be far enough away. As an undergraduate I worked as a field assistant on a pronghorn project in Montana. We hiked up hillsides and watched for females to get their babies out of hiding to nurse. We used binoculars and spotting scopes so we could see well enough to note ear tag colors, yet distant enough to not make the animals feel threatened by our presence.

With the pocket mice, that are so small, quick and nocturnal, getting far away and sitting quietly doesn’t work very well. I spent a dozen or so nights trying, outfitted with a camp chair and night-vision goggles. I set out some seeds on a tray and hoped the pocket mice would come. With one exception, they did not. Those were some of the longest nights I have ever experienced, sitting in the dark, staring at nothing.


Andrea Sork, a field assistant, uses night vision goggles to observe a kangaroo rat. On the right is an infrared camcorder.

What ended up working was trapping them first and then putting the tiny rodents inside a clear arena with the seeds, so I could watch them through the sides. While it isn’t perfect—they spend time exploring the walls and digging to get out—it at least allowed me to see them! And most of the animals decided that the seeds inside the arena were worth taking; even though I was sitting 12 feet away, the mice made multiple trips to the seed pile and back to their burrow. It helped that I sat very still and quiet the whole time. But it was exciting watching the animals come and go!

In addition to physically watching the pocket mice, camera traps can be hugely important. You can set multiple cameras at once and leave them for many nights. Later, as you go through the photos and videos, you can see where the mice were and what they were doing—especially if you leave food trays or set them at burrow entrances or some other specific place. The upside is that you can have a lot more “eyes” out at once, and cameras are less intrusive than a person sitting there. The downside, though, is that you can’t be sure cameras are catching everything, and they often have a pretty narrow view.

If you get a chance to see some animals in the wild, take an extra moment to watch them do their thing. Normal activities like sleeping or eating are a feat to witness, and there is so much to learn just by sitting still and watching!

Rachel Chock is a graduate student and volunteer with San Diego Zoo Institute for Conservation Research’s Pacific pocket mouse project. Read her previous post, Protected Habitat in Southern California.


CSI: Coronado


Feathers from a California least tern mark the scene of the crime. (Photo by Maggie Lee Post, courtesy Naval Base Coronado)

I never expected to gain detective skills on the California least tern and western snowy plover project. As field biologists, our observation skills are critical in assessing nest success, chick survival, and other aspects of population ecology throughout the season. There are times when we walk up to a nest and something is amiss: the eggs are missing, an egg is punctured, or sometimes we find only pieces of broken egg shell in the nest cup. This is when we get to an interesting aspect of our job: ‘crime scene’ investigation! Many predators try to take advantage of the hundreds of eggs in a tern colony and those in plover nests. We partner up with predator biologists to help solve these cases of nest predation and prevent more from happening.


Can you make out the American crow tracks left at this crime scene? (Photo by Billy Smith, courtesy Naval Base Coronado)

Early in the season this year, when the first nests were being filled in the tern colony, the common raven and American crow (members of the Corvidae family) were the main threats. Clues left at the scene of the crime included tracks, pieces of egg shell, and sometimes even remnants of yolk in and around the nest cup. Once these clever birds figured out that we used small green sticks to mark each well-camouflaged nest, they found several other nests at one site. We quickly changed our marking tactics, and began using sea shells to mark nests.

In the middle of the season, when the tern chicks were reaching that stage when they were just beginning to fly, we saw an increase in predation by raptors. Peregrine falcons and great horned owls were linked to some of the crimes. These skilled hunters make swift kills but leave messy crime scenes containing tracks, feather piles, and sometimes leftover pieces of their prey.

Birds are not the only hunters in the area. Skunks and other small, opportunistic mammals use their keen senses to find and eat tern and plover eggs. Since most of these terrestrial creatures forage around dusk or at night, we are able to detect tracks and other signs during our morning patrol—and we definitely smelled a skunk’s presence at one of the beaches! Skunks are especially problematic because they are capable of digging under the exclosures we place over the plover nests to get to the eggs.

Predator management is no easy task, and the predator biologists do an excellent and professional job. They come up with inventive scare tactics and other methods to alleviate the pressure on our protected birds. Our partnership gives the terns and plovers a chance to incubate their eggs and raise their chicks in peace. This is why I’m out here using my detective skills to help the terns and plovers nest successfully on the beaches of Coronado. Case closed.

Melissa Murillo is a research associate at the San Diego Zoo Institute for Conservation Research.


Conservationists Exploring Possibility of Recovering Lost Genetics Through New Technology; Plan Created to Rebuild Depleted Genetic Population of Black-Footed Ferret

Global_logo_color webNew reproductive technologies are being cited as a way to restore some of the genetic diversity lost in endangered species. A team of conservationists has developed a plan using somatic cell nuclear transfer to bring back the genetics of individual animals that are now preserved only in frozen cell culture banks. Using their genetic material could provide increased genetic variation for future generations of their species, which could counteract the effects of having a severely limited breeding population. A plan to undertake this effort with the critically endangered black-footed ferret was published in the September issue of the Journal of Heredity and can be seen at http://m.jhered.oxfordjournals.org/content/106/5/581.full.

“The importance of banking cell cultures from endangered species, such as in our Frozen Zoo®, is vividly demonstrated in this perspective article,” said Oliver Ryder, Ph.D., director of the Genetics Division at the San Diego Zoo Institute for Conservation Research, a co-author of the paper.

The critically endangered black-footed ferret is native to North America. The species has been reduced to only a few hundred individuals, and black-footed ferrets are currently being bred in accredited zoos and released into the wild. All black-footed ferrets are managed by the U.S. Fish and Wildlife Service. Susceptible to sylvatic plague, the species continues to remain on the brink of extinction, and it is kept alive through the dedication of conservationists.

If successful with the black-footed ferret, the technique could be used with a number of other species whose populations have been drastically reduced to the extent that important genetic diversity has been lost.

“This is the most endangered mammal in America. Using cryopreserved specimens to enrich its gene pool would open up a whole new avenue for conservation,” said Stewart Brand, co-founder of Revive& Restore, a San Francisco-based nonprofit that is helping with the genetic rescue of the black-footed ferret.

Bringing species back from the brink of extinction is the goal of San Diego Zoo Global. As a leader in conservation, the work of San Diego Zoo Global includes on-site wildlife conservation efforts (representing both plants and animals) at the San Diego Zoo, San Diego Zoo Safari Park, and San Diego Zoo Institute for Conservation Research, as well as international field programs on six continents. The work of these entities is inspiring children through the San Diego Zoo Kids network, reaching out through the Internet and in children’s hospitals nationwide. The work of San Diego Zoo Global is made possible by the San Diego Zoo Global Wildlife Conservancy and is supported in part by the Foundation of San Diego Zoo Global.




‘Insurance Population’ of Rare Bird Successfully Started through San Diego Zoo Global Program

Global_logo_color webFourteen fledglings flutter about in San Diego Zoo Global’s aviaries in Hawai‘i, under the care of conservation biologists. These young birds represent hope for a small Hawaiian bird species known as the ‘akikiki. The group represents the first of this species to be reared in a captive environment and the beginning of a breeding program designed to save this species from extinction.

“The ‘akikiki has shown steep declines over the past 10 to 15 years, and now numbers fewer than 500 birds,” said John Vetter, Forest Bird Recovery Coordinator of the State of Hawai‘i Department of Land and Natural Resources’ (DLNR) Division of Forestry and Wildlife. “A panel of experts in Hawaiian forest bird conservation was convened to identify steps needed to preserve this species, and ranked the initiation of a captive breeding population as one of the highest priorities for its survival.”

‘Akikiki eggs were brought to the San Diego Zoo Global facility earlier in 2015 through a collaborative effort with the Kaua‘i Forest Bird Recovery Project (KFBRP), Hawai’i’s DLNR Division of Forestry and Wildlife, and the U.S. Fish and Wildlife Service-Pacific Islands Fish and Wildlife Office (USFWS-PIFWO). Very little is known about this species, and these birds have not been raised in a zoological setting before. However, conservationists with San Diego Zoo Global have worked successfully with a number of other similar native Hawaiian birds and are using these techniques to ensure that the species will thrive.

“Using another species that we previously worked with as a model, we were able to successfully rear these 14 ‘akikiki at our centers in Hawai‘i,” said Bryce Masuda, Conservation Program Manager, San Diego Zoo Global. “This group of young birds will start a breeding population, protected in captivity from the threats bringing this species to the brink of extinction in the wild. Their presence provides insurance that we can protect this species now, for future generations.”

The ‘akikiki is a species of Hawaiian honeycreeper found only on the island of Kaua‘i. This species has been severely affected by introduced diseases such as avian malaria, loss of native forest habitat, hurricanes, and the introduction of non-native predator species in the wild.

“We are currently working with partners to address the threats to ‘akikiki in the wild, in order to ensure a successful reintroduction in the future,” said Michelle Clark, Biologist, Pacific Islands Fish and Wildlife Office.

Bringing species back from the brink of extinction is the goal of San Diego Zoo Global. As a leader in conservation, the work of San Diego Zoo Global includes onsite wildlife conservation efforts (representing both plants and animals) at the San Diego Zoo, the San Diego Zoo Safari Park, and San Diego Zoo Institute for Conservation Research, as well as international field programs on six continents. The work of these entities is inspiring children through the San Diego Zoo Kids network, reaching out through the Internet and in children’s hospitals nationwide. The work of San Diego Zoo Global is made possible by the San Diego Zoo Global Wildlife Conservancy and is supported in part by the Foundation of San Diego Zoo Global.

KFBRP is a collaboration between the Pacific Studies Cooperative Unit of the University of Hawai’i and the DLNR Division of Forestry and Wildlife. KFBRP’s mission is to promote knowledge, conservation of Kauai’s native forest birds, with a particular focus on the three endangered species: Puaiohi, ‘Akikiki and ‘Akeke‘e. For more information, please see www.kauaiforestbirds.org. The mission of the Department of Land and Natural Resources’ Division of Forestry and Wildlife is to responsibly manage and protect watersheds, native ecosystems, and cultural resources and provide outdoor recreation and sustainable forest products opportunities, while facilitating partnerships, community involvement and education.

The mission of the U.S. Fish and Wildlife Service is working with others to conserve, protect, and enhance fish, wildlife, plants, and their habitats for the continuing benefit of the American people. The mission of the Pacific Islands Fish and Wildlife Office is to conserve and restore native biodiversity and ecological integrity of Pacific Island ecosystems for the benefit of present and future generations through leadership, science-based management, and collaborative partnerships.

For more information, visit www.fws.gov/pacific, or connect with us through facebook.com/USFWSPacific, twitter.com/USFWSPacific/, tumblr.com/blog/usfwspacific, flickr.com/photos/usfwspacific/ and youtube.com/user/USFWS.


Terns, Plovers, and People: Living in Harmony


This beach on Naval Base Coronado is one site where field biologists are studying California least tern and snowy plover populations (U.S. Navy photo by S. McLaughlin, SDZG)

As field biologists, we are lucky to have some of the most beautiful offices in the world. Every day, my coworkers and I get to enjoy long walks on the beach, warm sunshine and the occasional passing dolphin pod. Of course with views like the one in the photo, we are working alongside many other people enjoying a day at the Pacific Ocean. It’s wonderful to see people appreciating the beach habitat we all love so much, especially when it’s done in a respectful and responsible way. So, here are a couple of thoughts from a field biologist.

Both the California least tern and western snowy plover are sensitive to human disturbance. While some bird species will remain on their nest until you are very nearly upon it, terns and plovers seem to hop off at the first sign of danger. Plovers can be seen in the vicinity of the nest, performing the broken-wing display to draw perceived predators away from their nest. Terns take a more aggressive approach, screeching at and dive-bombing anyone that approaches their nest; sometimes several members of the colony will join in to drive the threat away. With the numbers of terns and plovers at critically low levels, it’s important that the birds are able to spend their energy caring for their young, instead of chasing off disturbances.


With chicks this cute and helpless, it’s easy to see why we want to protect California least tern populations. (U.S. Navy photo by S. McLaughlin, SDZG)

The most common instances of disturbance we see out in the field are people walking through the colony and dogs being allowed off leash in areas with nesting birds. In addition to upsetting the adult birds, these types of disturbances can result in trampled eggs and chicks, and stressed-out young. Luckily for all the recreational beach users out there, avoiding creating a disturbance is very easy! The most important step to take is observing and abiding by posted signs. If you are ever approached by a game warden or field biologist, don’t be afraid to ask questions. We love to talk about the terns and plovers, and outreach is an important part of our jobs!

The beaches of southern California and the birds that live there offer amazing opportunities for people to engage with nature. If we enjoy these resources respectfully and responsibly they will hopefully be here for many more years to come.


Stephanie McLaughlin is a research associate at the San Diego Zoo Institute for Conservation Research.


Learning What We Can Learn from Camera Trap Photos: Part 1


Andean bears are sometimes called spectacled bears because of the rings of lighter colored fur around their eyes.

Others have said it before and it’s true: New forms of technology such as camera traps make it possible for field researchers to collect information we could previously only dream about. Technology advances so quickly that we’re still evaluating what we can do with these tools and what questions we can and cannot answer by using them. We have many basic questions that are still unanswered even for species as large as the Andean bear. Here are two of the most basic: How many are there? Are the populations increasing, stable, or decreasing? The answers to these questions and others would help researchers, conservationists, and governments decide how much of their limited resources to invest in research efforts and conservation actions, in the hopes that 100 years from now there will still be bears roaming the forests of South America. Unfortunately, there are still no answers to these questions.

How would you answer these questions? How do you count animals that live in dense forests in rugged habitat, when those animals avoid contact with humans? It’s been said for decades that the markings of individual Andean bears vary so much that you can identify each individual bear just by looking at it. If that’s true, then maybe we could use camera traps to identify individual Andean bears in photographs and then estimate population sizes and densities. However, how do you test whether individual bears can be reliably identified in photographs? In order to test this you’d need photos of a lot of different bears whose identity you definitely knew. That means you can’t just use photos of wild bears from camera traps, because you don’t know how many bears walked in front of the camera traps.


Compare the markings of this bear, Tommy, with the bear above (named Turbo) and notice the differences.

The only way we could think of to test this was to take photos of different bears from captivity, so we’d know the identify of the bears, ask people to compare those photos, and keep score of whether bears were correctly identified, or not. When a group of international collaborators and I did this we were surprised to discover that people were initially not very good at this task. In fact, they would have done just as well if they’d flipped a coin! That’s really not the kind of result we were expecting, or hoping, and it led us to consider whether we were over-confident in our own abilities to identify individual bears. However, it turns out that with a little practice and training, participants became better at identifying bears from their photographs. After thorough review and discussion by other scientists, this work has been published in the journal Wildlife Biology and you can read all the details and see more photos here.

So, the good news is that, if we’re careful, we and other field researchers can use photos from camera traps to identify individual Andean bears, estimate the sizes of their populations, and compare populations densities. Now, we “just” need to get the cameras into the forests where there are bears!

Russ Van Horn is a scientist at the San Diego Zoo Institute for Conservation Research. Read his previous blog, Ambassador Mi Ton Teiow Receives a New Posting.


Female Northern White Rhino Dies in Czech Republic: Only Four of These Rhinos Remain Worldwide

Global_logo_color webThe Dvur Kralove Zoo in the Czech Republic has announced that an elderly northern white rhinoceros, Nabiré, has passed away. The female rhino was born in 1983 and died July 27, 2015 from complications with a pathological cyst. Her death leaves only four northern white rhinos remaining in the world: an elderly female at the San Diego Zoo Safari Park, named Nola; and three under human care at the Ol Pejeta Conservancy in the African nation of Kenya: a male, Sudan; and two females, Najin and Fatu.

“Our condolences go out to the Dvur Kralove Zoo for this particularly difficult loss,” said Randy Rieches, curator of mammals for the San Diego Zoo Safari Park. “Watching this wonderful subspecies move one step closer to extinction breaks the hearts of all of us who have worked with and love rhinos.”

Northern white rhinos are at the brink of extinction because of poaching in Africa. Only a few have lived in zoological settings, and those animals have been largely non-reproductive.

San Diego Zoo Global is working to save the genome of this rhino subspecies through the collection of genetic material. Samples of 12 northern white rhinos are currently preserved in the Frozen Zoo® at the San Diego Zoo Global Institute for Conservation Research.

San Diego Zoo Global just received a $100,000 grant from the Ellen Browning Scripps Foundation to continue this research and rescue effort.

“After hearing about the plight of the northern white rhino, I shared San Diego Zoo Global’s plan for a genetic rescue of the species with the Scripps family,” said Doug Dawson, executive director of the Ellen Browning Scripps Foundation. “Instantly, we unanimously and enthusiastically agreed this is where we wanted to commit Miss Ellen’s philanthropic investment this year!”

In addition to the genomic research at the Institute for Conservation Research, a rhino rescue facility is being built at the San Diego Zoo Safari Park to house a colony of white rhinos, to ensure the preservation of the species. Those who want to contribute toward San Diego Zoo Global’s work to end extinction of the white rhino can visit www.sandiegozoo.org/rhino.

In the wild, rhinos are killed for their horns—a unique physiological feature made up of keratin, the same material that forms human hair and fingernails. Many cultures erroneously believe the rhino horn has medicinal value, so sadly, the illegal market in horns taken from poached animals continues to thrive.

Bringing species back from the brink of extinction is the mission of San Diego Zoo Global. As a leader in conservation, the work of San Diego Zoo Global includes on-site wildlife conservation efforts (representing both plants and animals) at the San Diego Zoo, San Diego Zoo Safari Park, and San Diego Zoo Institute for Conservation Research, as well as international field programs on six continents. The work of these entities is made accessible to children through the San Diego Zoo Kids network, reaching out through the Internet and in children’s hospitals nationwide. The work of San Diego Zoo Global is made possible by the San Diego Zoo Global Wildlife Conservancy and is supported in part by the Foundation of San Diego Zoo Global.



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.


No Ligers Here


San Diego Zoo Global is dedicated to helping to preserve—physically and genetically—endangered species like these Malayan tigers.

“What are you drawing?”

“A liger.”

“What’s a liger?”

“It’s pretty much my favorite animal. It’s like a lion and a tiger mixed…bred for its skills in magic.”

Napoleon Dynamite

I began working for the San Diego Zoo Institute for Conservation Research in the Reproductive Physiology department in 2003. After about a year, I noticed the most commonly asked question from kids touring the lab was: “Do you make ligers here?” I think we can thank the hit movie Napoleon Dynamite for that, but as the years have gone by, the question still arises often in many different forms. I think we all are fascinated to hear about animal hybrids—the mixing of two animals of different breeds, species, or genera—but what do hybrids mean to conservation and why do we not use our advanced reproductive technologies to create them in the lab?

There are many types of hybrids that exist such as intrasubpecific hybrids between two animals of different subspecies (like Bengal and Siberian tigers), interspecific hybrids between two animals from different species (for example, lions and tigers, resulting in a “liger” or “tigon”), and intergenic hybrids between animals of different genera (as happens when sheep and goats breed, resulting in a “geep” or “shoat”). While hybridization is often thought of as a man-made phenomenon, natural hybridization does occur. Most of us are familiar with mules, which are the product of a female horse mated with a male donkey. Mules are prized for their great strength and endurance, but all male mules and most female mules are incapable of producing offspring. This is common in hybrids because their genetic material is not perfectly matched. There is also a hybrid animal called the beefalo (prized for its meat) that is the offspring of a North American bison and a cow.

Those last two examples are domestic animal hybrids that possess traits valued by humans, yet there are many issues that occur when non-domestic animals hybridize. Wild animals have evolved over millions of years through natural selection, a process that increases the probability of survival and reproduction. Hybridization, however, can result in the loss of a morphological or behavioral trait that may be necessary for survival.

An example of this is when a mule deer that uses a “stotting” escape strategy breeds with a white-tailed deer, which employs a galloping escape strategy. The hybrid offspring inherits a slow and inefficient gait, making it vulnerable to predation. And in cases where domestic cats that have gone feral breed with wild cats, the offspring are not as genetically strong and this can affect their resistance to disease.
As climate changes occur and humans modify animal habitats, wild hybridization may become common. One such example is the “grolar bear”—the offspring of a grizzly and polar bear—that was seen in Canada. This hybrid could occur more frequently as polar bears, driven from their typical range due to melting sea ice, spend more time in grizzly territory.

If hybridization sometimes seems to create a more “fit” animal or occurs in the wild occasionally, why don’t we use our laboratory skills to create them? We have the ability to inseminate the egg of one animal with sperm from another closely related species and grow an embryo that could be placed into a host female of either species. But we don’t, simply because San Diego Zoo Global’s mission is to save species worldwide by combining our expertise in animal care and conservation science with our dedication to inspiring passion for nature. We are in the business of saving species not creating new ones.

There are exceptions to this rule, such as when a population becomes so small that it can no longer sustain itself. In this case, scientists may agree that hybridization with a closely related subspecies is the only chance for survival. This has been attempted with the Columbia Basin pygmy rabbit and its close cousin, the Idaho pygmy rabbit. The Florida panther population was brought back from the brink of extinction by releasing female Texas cougars into the habitat for hybridization—the result was a three-fold increase in the number of Florida panthers, and the hybrid offspring were genetically healthy, stronger, and longer-lived.

So, I am afraid you will not see any ligers or grolar bears being created in our lab but that is because we are working hard to help tigers, lions, polar bears, and grizzly bears maintain or grow their populations. We think they are pretty amazing just the way they have evolved.

Nicole Ravida is a research laboratory technician at the San Diego Zoo Institute for Conservation Research. Read her previous blog, No Scientist is an Island.