Saving The Boreal Toad
Cheyenne Mountain Zoo
Colorado Springs, Colorado
The boreal toad is found throughout much of Colorado with at least one known breeding site in southern Wyoming. There is a recent report of a boreal toad observation in northern New Mexico where they were thought to be no longer found.
Within Colorado there are at least 50 known breeding sites comprising up to 30 separate populations. There are at least four “metapopulations” that have been identified by researchers. These are located in Chaffey County, Clear Creek County, Summit County and in Rocky Mountain National Park.
The boreal toad is the only native Colorado amphibian species that lives exclusively at elevations of 8,000 to 12,000 ft.
The population of these amphibians has declined dramatically over the past 25 years. The decline has been attributed to several possible causes. These include: increased UV radiation, acidification of water, water borne toxins, heavy metal contamination, habitat disturbance, and most recently a pathogenic chytrid fungus called batrachochytrium dendrobatidis.
Status in the Wild
The boreal toad has been listed as endangered in the state of Colorado since 1993. It is “warranted but precluded” by the federal agencies. This means that there is adequate data indicating the need for federal listing as endangered or threatened. However, listing has been postponed as there are species in greater need of listing at this time.
The Chytrid Fungus
The greatest concern for the wild boreal toad populations at this point involves the chytrid fungus mentioned earlier. A large amount of research and resources has been dedicated to understanding why and how this fungus is responsible for the decline of this particular toad. Until we can easily detect, treat, and/or prevent this pathogen from causing irreparable mortality to the wild populations, we must prepare for the worst case scenario.
This fungus was first identified in 1998 by Dr. Earl Green and others. Dr. Green is a wild life pathologist with the USGS. They determined that this fungus was observed in a wide range of the amphibian population with die-offs in Panama and Australia. The fungus has also been identified in some amphibian populations in Arizona and has caused the death of many zoo amphibians in the United States.
Scientists don’t know how this fungus is transmitted from one area to another, let alone why the fungus is affecting amphibian populations around the world. Whether the chytrid fungus is responsible for the frog or toad mortality or the declines of frogs and toads in many western states is still unknown. Green emphasizes that diagnostic tests on the boreal toads are still being completed, and that additional infectious diseases or other possible causes of death may yet be found in this population. Because fungal infections are considered secondary infections in other vertebrates, USGS is completing further tests for viruses, parasites and bacteria to rule out other factors that could predispose the animals’ susceptibility to the fungus.
Sick and dying toads in our Colorado population were first discovered in May of 1999. The problem was uncovered by Colorado Division of Wildlife researchers. They have been intensively studying the animals for the last 5 years. Dead toads have been found every month at the site, which is on private lands west of Denver. USGS researchers said they have identified chytrid fungus in many of the dead and living toads they examined from the site in 1999. Live toads show few clinical signs of the disease, but some may appear weak, lethargic and reluctant to flee at the approach of humans. Upon being examined microscopically many of the dead toads showed a myriad of minute chytrid fungi in the skin of the abdomen and toes. The microscopic identification of this fungus is being confirmed in collaborative work by Dr. Joyce Longcore., She is a world-renowned chytrid expert at the University of Maine.
Questions yet to be answered regarding the chytrid fungus are numerous. Where did the chytrid fungus come from? We know that there are about 80 species of chytrid fungus world wide, which feed on algae, plant material, keratin, etc. But how did the amphibian chytrid come to be toxic to the boreal toad? Did it mutate from another chyrid? Was it altered by environmental conditions to become toxic? How does chytrid kill amphibians? Does it suffocate them? Does it poison them? Does it alone kill the toad or does it cause something else to happen which kills the toad? Why does chytrid kill all the toads in a specific area and not another? Has chytrid fungus always been around but not active all the time, or has it come from somewhere else and is being spread by something such as another host, weather patterns, people, etc.? Or is this a new disease which is being spread? Much research needs to be done needless to say.
Boreal Toad Recovery
The Colorado Department of Wildlife has developed a comprehensive recovery plan for the boreal toad with representation and involvement from the following agencies: U. S. Geological Survey/Biological Resources Division, U.S. Forest Service, Bureau of Land Management, U.S. Fish and Wildlife Service, Colorado Dept. of Wild Life, and Colorado State University.
To understand the complexity of a recovery program, we need to examine the habits of the boreal toad. They have a lot of bad habits. Toad to toad contact may serve to spread diseases like the chytrid fungus. All adult males and females ready to lay eggs gather in masse at aquatic breeding sites in the spring. Males enthusiastically grab at everything that remotely resembles a female toad, sometimes forming mating balls.
This makes it possible for infections to spread. After breeding season is over, the toads often disperse to sheltered sites such as rodent burrows, which they share with other toads. Adult toads also hibernate communally, sometimes in the same burrows where they spent the summer. Even metamorphosed toadlets have behaviors that may serve to transmit the chytrid fungus from one toadlet to another. They gather into piles to conserve water and maximize their body temperatures. If any one of these toadlets is infected, this behavior presents yet another opportunity to pass along the fungus.
Finally, we do not currently know whether this toad to-toad contact is even necessary to transmit the disease. It is possible that even the water or mud around breeding sites may be enough for the chytrid to infect a toad. For this reason, people conducting amphibian surveys decontaminate all equipment—such as boots and nets—with bleach before going to another amphibian site.
The main points of the boreal toad recovery plan are as follows:
1. Conducting surveys of historic and potential habitats for new boreal toad populations
2. Regular monitoring of known breeding populations
3. Research to identify and evaluate factors limiting toad survival
4. Research to better define suitable boreal toad habitat
5. Development of captive breeding and rearing of boreal toads
6. Experimental introductions to historic habitats
7. Protection of habitats via coordination with land management agencies
8. Increase public awareness through education and public involvement in searches for new populations
9. Continued research on the chytrid fungus such as treatments, diagnostics, prevention causes, etc.
The Future of the Boreal Toad
The Colorado Dept. of Wildlife has recently completed a Native Aquatic Species Restoration Facility near Alamosa in southern Colorado. This facility has had great success in hatching out clutches of toad egg masses from various population sites and raising these tadpoles into young adult toads. The intention of this “head-start” program is to provide and maintain a large number of captive stocks from as many populations as possible in order to ensure the integrity of the genetic diversity of each population through controlled breeding and release programs.
The boreal toad recovery team hopes to recruit assistance in the raising and breeding of select populations of toads from AZA accredited institutions, in an effort to have the greatest genetic variability possible in case of disastrous die-offs of wild populations. Currently there are several institutions already involved, including the Cheyenne Mountain Zoo, the Henry Doorly zoo, the Toledo Zoo and Oceans Journey in Denver.
The greatest concern for the wild populations at this point involves the chytrid fungus mentioned earlier. A large amount of research and resources have been dedicated to understanding how and why this fungus is responsible for the decline of the boreal toad and other wild anurans. Until we can easily detect, treat, and/or prevent this pathogen from causing irreparable mortality to wild populations, we must prepare for the worst case scenario. By combining field research and intense captive propagation, we may be able to prevent the extinction of this species in the wild.