A Partnership for Endangered Toads

Denver Zoo and Colorado Parks and Wildlife release endangered boreal toad tadpoles into high-altitude wetlands in Gunnison National Forest.
CPW's Daniel Cammack, left, works alongside staff from the Denver Zoo to stock boreal toad tadpoles on June 28, 2022. Photo courtesy of Denver Zoo.
Colorado Parks and Wildlife’s Daniel Cammack, left, works alongside staff from the Denver Zoo to stock boreal toad tadpoles on June 28, 2022. Photo courtesy of Denver Zoo.

Last November, Denver Zoo and Colorado Parks and Wildlife (CPW) launched a new initiative aimed at boosting the state’s population of boreal toads, a species listed as endangered in Colorado and New Mexico. Starting with 95 adult toads from Colorado Parks and Wildlife’s Native Aquatic Species Restoration Facility in Alamosa, experts from the Zoo spent more than six months preparing the toads for breeding, and nurturing their offspring leading up to their release into the wild. On Tuesday, June 28, teams from the Zoo and CPW trekked to a remote site in Gunnison National Forest to introduce 570 tadpoles into wetlands that officials hope could eventually host an established population of rare amphibians.

Boreal Toads Face Uncertain Future

“This was the result of a tremendous amount of hard work and planning by our partners at Colorado Parks and Wildlife, and members of our animal care and field conservation teams,” said Erica Elvove, Senior Vice President for Conservation Engagement and Impact at Denver Zoo. “Boreal toads face an extremely uncertain future in Colorado and have a good chance of going extinct without human intervention. We’re committed to continuing this effort with CPW for many years to come, and doing our part to make sure the species remains part of Colorado’s ecosystem for future generations.” 

1-year-old boreal toad
A 1-year-old boreal toad is pictured in the wetlands where boreal toad tadpoles were recently stocked by the Denver Zoo and CPW. John Livingston/CPW

Once common in montane habitats between 7,000-12,000 feet in the Southern Rocky Mountains, the boreal toad has experienced dramatic population declines over the past two decades. The decline appears to be related to habitat loss and primarily infection by the chytrid fungus, which can infect the majority of the world’s 7,000 amphibian species, and is linked to major population declines and extinctions globally. Officials estimate there may be as few as 800 wild adult toads left in Colorado.  

“It was a very special day to join our partners from Denver Zoo to release boreal toad tadpoles that the Zoo produced at their facility,” said Daniel Cammack, Southwest Region Native Aquatic Species Biologist with CPW. “We’ve been stocking tadpoles at this site for about five years now, and we have high hopes that the tadpoles we introduced will contribute to a self-sustaining breeding population. It’s a pretty big win for boreal toad conservation.”

Conserving Endangered Amphibians

Denver Zoo has been conserving endangered and critically endangered amphibian species for more than 15 years. In 2018, the Zoo became the first zoo in the Northern Hemisphere to successfully breed critically endangered Lake Titicaca frogs, and has since provided more than 250 healthy frogs to zoos and aquariums in the U.S. and Europe. In 2019, the Zoo used a hormone treatment to breed and produce more than 600 boreal toads, which were released in a remote area in southwestern Utah. And in 2021, the Zoo successfully bred critically endangered Panamanian golden frogs as part of the Association of Zoos and Aquarium’s Species Survival Plan. 

CPW has devoted significant resources in the past 20 years toward researching the cause of boreal toad declines in the state and exploring ways to recover the species. Specifically, CPW researchers focus on developing methodologies for reintroducing toads in historically occupied habitats, detecting chytrid fungus in the wild, marking and identifying individual toads and improving breeding success at the Native Aquatic Species Restoration Facility, which plays a critical role in the state’s efforts to restore populations of boreal toads.

4-year-old boreal toad
A boreal toad estimated to be a 4-year-old is pictured in the wetlands where boreal toad tadpoles were recently stocked by the Denver Zoo and CPW. John Livingston/CPW

“The boreal toad is a really unique amphibian,” Cammack said. “We are up at 11,500 feet at timberline practically, and they are gutting out these big winters covered by snow. They are an integral part of the landscape and were ubiquitous once in Colorado in this habitat. With chytrid fungus now being the primary cause of decline, we don’t have that many populations of boreal toad remaining. For us to get something else going is really important.”

A Long Road Ahead

Officials from the Zoo and CPW estimate that it will take many years to bring the species back to a level where it is secure in the Southern Rocky Mountains, and expect the collaboration to be a multi-year program. Additionally, as part of the wild release program, the Zoo launched a community science project where volunteers monitor the species’ high-country habitat to help officials understand the health of current wild populations and determine suitable locations for future reintroduction of toads bred at the Zoo. For more information, visit DenverZoo.org/Boreal-Toad-Conservation-Team

“As someone who grew up in Colorado and loves wildlife, I like to think about what it would be like to jump in a time machine before there were big population centers and see what wildlife looked like on the landscape,” Cammack said. “These are the critters that were here. Now with boreal toads and other native fish and things that I work with, they’ve declined so far that they only occupy a fraction of what they once occupied. It’s a good crusade, in my opinion, to try to conserve even a fraction of what was and keep these creatures represented on the landscape. They have an inherent right to exist.”

Home to almost 3,000 animals representing more than 450 species, Denver Zoo is a non-profit 501©(3) organization and the city’s oldest and most passionate advocate for the natural world. The Zoo is among the most visited cultural destination in Colorado, serving almost 2 million people per year, and accredited by the Association of Zoos and Aquariums (AZA), which assures the highest standards of animal care. With the mission inspiring communities to save wildlife for future generations, Denver Zoo dedicates almost $2 million annually to Zoo-led programs aimed at protecting animals within their natural habitats around the world. For more information, visit DenverZoo.org.

Written by John Livingston and Jake Kubié. John is the Southwest Region Public Information Officer for Colorado Parks and Wildlife and Jake is the Director of Communications for the Denver Zoo.

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