Long-term egg mass surveys show that northern red-legged frogs are in decline

By Amelia Hesketh

May 18, 2023

As winter turns to spring each year, many amphibians in southern British Columbia dutifully make their way from their forest homes to wetlands under the cover of night. Females carefully lay their jelly-covered eggs around the stems of grasses, reeds, and other vegetation near the wetland shore, where the eggs remain until they hatch, releasing the tadpoles within.

Each year since 2009, the A Rocha BC Conservation Science team has journeyed to wetlands alongside amphibians to monitor populations of northern red-legged frog (Rana aurora), a species of special concern within the Tatalu watershed. Red-legged frogs consume algae and insects, maintaining the abundance and diversity of these prey within wetlands, and serve as an important source of food for birds and snakes. This year, we visited 11 wetlands every week with a crew of fantastic volunteers to count frog egg masses. Because a female northern red-legged frog can lay only one egg mass each year, we can use our count data to determine how many females bred in each wetland. We were delighted to find red-legged frog egg masses in 9 of our surveyed wetlands, including 67 egg masses in a single wetland! However, when we compared this year’s data to counts dating back to 2015, we found that the number of egg masses we observe each spring — and thus the breeding population of red-legged frogs — has decreased steadily over time. 

These changes, while alarming, are a call to action. Amphibian population declines can be caused by loss of forest and wetland habitat from development, warming temperatures due to climate change, or a combination of these and other impacts. To protect this imperiled species and amphibians like it, we must steward our existing forests, construct new wetlands to replace those lost through urbanization, and restore degraded habitat. Over the years, A Rocha has supported these efforts by constructing new wetlands and restoring forest habitat, both at Brooksdale Environmental Centre and within the broader Tatalu watershed. In protecting species-at-risk, we are responding to our personal and biblical call to steward God’s earth.