Qu'est-ce que le Programme de rétablissement de la grenouille maculée de l'Oregon ? Since 2010, WPC has been breeding the endangered Oregon spotted frog at the Greater Vancouver Zoo, and reintroducing thousands of tadpoles and froglets back into wetlands in B.C.’s Fraser Valley. It takes years of careful observation, collaboration, ingenuity and sometimes a little luck to crack the code to breeding specific species. For several years, our progress was very limited. But our team persevered. Today, WPC has pioneered breeding techniques that are turning the tide for this species.
The 2025 Oregon spotted frog breeding season has already been an interesting year. We had 21 egg masses produced, which is great, but we also had lower overall fertilization success this year – likely due to the young age of some of the new females in the breeding colony.
Since the loss of half of our female frogs to chytrid fungus in 2021 we have been rebuilding the captive breeding colony, particularly females, and in 2025 we were able to introduce some new females into this breeding group.
We also learned at the beginning of breeding season when the frogs went into breeding hugs or “amplexus”, that we had made some errors determining the sex of the animals as there were suddenly 6 males in our female tank! These lucky fellows spent the entire winter surrounded by females. This is likely due to the way juvenile males are identified which can apparently be difficult to do when they are just reaching maturity. To ID males we look for black pads on their front thumbs, called “nuptial pads” that assist them in grasping females (pictured below). Clearly some of our males had yet to develop these pads and were tricking us into thinking they were females! This may have thrown off the water chemistry of our mystical “magic water” which is normally full of female hormones and has led to the high fertility rates in previous years. We also suspect that some of our new young females may need to be another year of two older to be up to producing large viable egg masses, only time will tell.
Male Oregon spotted frog with nuptial pad on thumb (darker coloured pad). Photo: A. Gielens
Female Oregon spotted frog, no nuptial pad on thumb. Photo: A. Gielens
Fortunately, we still had high fertility in the egg masses produced by the older females which produced a total of 4,500 tadpoles. 3,500 of these were released in April during an incomplete release (we are holding onto about 1,000 tadpoles in our facilities for later release) and we also kept an additional 300 for captive rearing and “quality control”.
Releasing these tadpoles into a restored habitat that has been our release location for quite a few years now, our spirits were boosted by an amazing observation… the frogs we had released in previous years have been busy creating egg masses. In fact, the number of egg masses had nearly tripled this year and 15 egg masses in total were recorded. This is no doubt a result of the sheer number of tadpoles we have been able to release onsite over the last five years, which has really set this site up for success.
In addition to a lovely day releasing thousands of tadpoles, we’ve also had a few heart-warming moments on site this year already. After trialing egg mass translocations this spring which involved moving egg masses to the release site before they hatch – carefully placing the masses in the traditional laying sites or sites the frogs would likely choose naturally, we noticed something exciting. Only one day after moving the egg masses to the wild, we noticed that some wild female frogs had added their egg masses to the translocated ones… our eggs were accepted as wild ones! Within the week we also saw a wild male calling from a cluster of eggs masses, including some translocated eggs. This means our egg masses and frogs are truly blending in well with their landscape.
By investigating how the next generation of frogs are doing at our release sites (the babies of the frogs we released), we are monitoring the eggs hatching success in the wild compared to the exsitu egg hatching back at our facilities at the Greater Vancouver Zoo. This is the next stage in determining how to best help this species recover.
Andrea Gielens releases a bucket full of tadpoles into the wetland. Photo: Creo Digital
(Left) Jag Athwal, Assistant Biologist for our B.C. Projects, and (right) Andrea Gielens, Lead Biologist for our B.C. Projects stand together at our release site. Photo: Creo Digital
A wild Oregon spotted frog is held in hand at the release site. Photo: Creo Digital
Andrea manages WPC’s captive breeding and release programs for the Oregon spotted frog and the coastal western painted turtle. Andrea has studied at-risk reptiles and amphibians in Canada and abroad, including a term at the Durrell Wildlife Conservation Trust in Jersey. Andrea also manages the Taylor’s checkerspot butterfly recovery program in BC.
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