On September 3, 2025, eight eager members of our team set out into wetlands in the East Kootenays of British Columbia to catch as many Northern Leopard Frogs (Lithobates pipiens) as we could get our hands on. Equipped with frog nets and a clear goal, we set out to reduce the devastating impact of a fungal disease known as chytridiomycosis (hereafter “chytrid”), which has led to the loss or decline of over 500 amphibian species globally (1).

How did we plan to tackle this challenge? With a simple treatment: a bath. To understand why, we first need to look at how we got here.

Background

Northern Leopard Frogs are one of the most widely distributed amphibian species in North America. However, they have experienced significant declines in the western part of their range in recent decades due to stressors like chytrid (2). The focus of our program is on the geographically and genetically distinct Rocky Mountain Population of Northern Leopard Frogs in British Columbia, Canada. With only a single extant population remaining, they are considered endangered federally and critically imperiled provincially.

Protecting this remaining population is critical to the recovery of the species in British Columbia. As part of the British Columbia Northern Leopard Frog Recovery Team, our goal at the Wilder Institute is to prevent the local extinction of these frogs through conservation translocations that reintroduce them to areas within their historical range.

In 2022, the program switched gears and we started releasing at a promising new reintroduction site near Kimberley, British Columbia. This site was selected following extensive habitat assessments the previous year to ensure it would meet all of the Northern Leopard Frog’s seasonal habitat requirements. We were hopeful when we saw early signs of success, including very high tadpole to young-of-year survival (~20%, compared to 4–6% reported in the literature for similar species; 3, 4) and a large body size in recently metamorphosed frogs – similar to what is often seen in two-year-old Leopard Frogs! However, when spring 2023 came around, we did not find any overwinter survivors and began to suspect that chytrid might be playing a role.

To investigate whether chytrid was the culprit we suspected, we conducted a prevalence study in 2023 where skin swabs were collected from all frogs captured during three survey weeks in late summer. We collected 87 swabs in total, of which only 35 were from frogs that showed clinical signs of chytrid. Despite this, every single swab came back positive for the fungus. Late fall surveys in the overwintering habitat only further confirmed just how dire the situation was. We detected six dead frogs, all of which were confirmed to have had chytrid.

So how did we deal with the devastating news of 100% chytrid prevalence at our reintroduction site? We took on an ambitious challenge: treating frogs in the wild!

In situ treatment for chytrid

In September 2025 – we returned to the wetlands and captured 68 young-of-year frogs. Fifty-three of these were designated for daily treatment baths with itraconazole (an anti-fungal agent), while the remaining 15 served as controls. Because holding frogs in close proximity without treatment could increase infection intensity, we did not hold the controls for the same duration as the treatment frogs. Instead, control frogs were held for only 15 to 30 minutes before being released back into their wetlands of capture.

Treatment frogs were held for seven days in spacious, furnished pens along the edge of a wetland, providing access to both terrestrial and aquatic habitats. Each day, frogs were collected daily and visually inspected for clinical signs of disease or other injuries, before being placed in a 20-minute treatment bath with their other pen pals. Following treatment, we rinsed the frogs with wetland water and returned them to their holding pens.

Four green mesh holding pens partially submerged along a wetland edge in low evening light, with forested hills and mountains behind
View of the holding pens partially submerged along the wetland edge. Photo: The Wilder Institute

Treatment results and long-term survival

Before treatment began, 75% (40 of 53) of frogs tested positive for chytrid fungus. After the final treatment on day seven, only 9% (5 of 53) still tested positive. Notably, one of these five individuals tested negative upon follow-up testing two weeks later. In other words, at least 49 frogs were chytrid free following the treatment!

But we were not done yet. Several weeks after treatment, we managed to recapture and swab another 10 frogs – eight treated frogs and two controls. All eight treated frogs remained negative in the weeks following treatment. Of the two control frogs, one started negative and remained negative, while the other started positive and remained positive.

Northern Leopard Frogs at the water surface among reeds inside a mesh holding pen, photographed at water level
Northern Leopard Frogs inside of the holding pen between daily treatments. Photo: The Wilder Institute

Now jumping ahead to spring and summer of this year, we were eager to get out and determine whether any of these treated frogs had survived the winter. Prior to this year, there had been only one confirmed overwinter survivor at the reintroduction site. However, in 2026, 14 juvenile frogs were confirmed to have survived the winter! Even better, 12 of these 14 frogs had undergone chytrid treatment in 2025, resulting in an overwinter survival rate of 22.6% among frogs involved in the treatment. In comparison, we have only confirmed survival of two frogs that weren’t part of the treatment; based on capture-mark-recapture data, an estimated 516 untreated frogs were present at the site in 2025, resulting in an overwinter survival rate of 0.4% for this group.

Building on the first year’s success, we plan to do this all over again in September 2026, this time treating twice as many frogs. We have high hopes that the associated improvements in frog health and overwinter survival, along with potential future resilience to infection, can contribute to the long-term success of the reintroduction site and recovery of the small but mighty Northern Leopard Frog in British Columbia.

A Northern Leopard Frog at the surface of a shallow wetland pool among aquatic plants, with distant mountains and blue sky beyond
Northern Leopard Frog relaxing in its wetland habitat at the reintroduction site. Photo: The Wilder Institute

Unexpected challenges: feeding

While the treatment was successful in reducing the number of disease-positive frogs and improved overwinter survival, that was not our only victory. Despite our worry that frogs would lose their appetites during the treatment, a whopping 70% gained weight throughout the process! Feeding these frogs was no small feat and required a combination of dedication, creativity, and patience.

The diet provided during the treatment was a combination of purchased mealworms as well as wild grasshoppers and crickets caught onsite. The mealworms were easier to acquire but harder to feed to the frogs; simply placing them in a feeding dish was not sufficient. Wild frogs are not used to obtaining food this way and seem to struggle to spot the perfectly laid-out prey.

Our field team had to get creative, with each person developing their own method for feeding the frogs mealworms. Some preferred hand-feeding with tweezers, wiggling the worms in front of the frogs. Others gently placed a spatula in front of them, offering a feast of squirming worms – kitchenware can be surprisingly useful in field settings! Some frogs were more skittish and required more patience (and back pain) to tempt into eating, while others were so eager that they had to be stopped from going back for second or even third helpings.

A gloved hand offering a mealworm with forceps to Northern Leopard Frogs resting on green mesh inside a holding pen
Field staff handfeeding mealworms to frogs with forceps. Photo: The Wilder Institute

Grasshoppers and crickets were also provided to imitate the frogs’ wild diet. Our field team spent a couple of hours each day catching nearly 100 insects and releasing them into the husbandry pens. The frogs were no strangers to these hoppers and typically started feasting immediately.

In the end, the treatment was about more than reducing disease prevalence. It was a lesson in adaptability, for both the frogs and the field team, and a reminder that conservation success often hinges on small, patient acts repeated day after day.

Acknowledgments

This work would not have been possible without the contributions of all of our great team members and collaborators. The field work involved was made possible by the skill and dedication of Hillary Hale, Erin Gilbert, Kevin Park, Llewellyn Haines, Natalia Porro, and Sienna Beaulieu.

The chytridiomycosis treatment protocol was acquired from our head veterinarian, Dr. Doug Whiteside at the Wilder Institute’s Calgary Zoo, who had successfully used this protocol to treat Northern Leopard Frogs under human care.

Reintroductions are made possible by the dedicated members of the British Columbia Northern Leopard Frog Recovery Team. The single remaining population of this endangered species is monitored by the hard work of the Fish and Wildlife Compensation Program staff. This extant population has become the source for reintroductions and for establishing conservation breeding populations at the Vancouver Aquarium, Wilder Institute, and Edmonton Valley Zoo.

Lastly, and perhaps most importantly, thank you to Lea Randall for your continued guidance, knowledge, and commitment to Northern Leopard Frog recovery.

Literature Cited

  1. Scheele, B. C. et al. Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity. Science 363, 1459–1463 (2019).
  2. Rorabaugh, J. C. Rana pipiens Schreber, 1782. Northern Leopard Frog. In Amphibian declines: the conservation status of United States species (ed. Lannoo, M. J.) 570–577 (Univ. of California Press, 2005).
  3. Berven, K. A. Factors affecting population fluctuations in larval and adult stages of the wood frog (Rana sylvatica). Ecology 71, 1599–1608 (1990).
  4. Biek, R., Funk, W. C., Maxell, B. A. & Mills, L. S. What is missing in amphibian decline research: insights from ecological sensitivity analysis. Conserv. Biol. 16, 728–734 (2002).