Hope for California Red-legged Frogs After Woolsey Fire Devastation

Remarkably, surveys a couple of weeks after the Woolsey Fire turned up lots of frogs on the scorched landscape around the Simi Hills pools (pictured). Biologists also found one frog at each of the burned translocation sites.

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July 2019 - In November 2018, the Woolsey Fire burned a whopping 42% of the natural area in the Santa Monica Mountains, including 88% of National Park Service lands. No species escaped unscathed. One or more mountain lions perished in the fire or its aftermath. Entire bobcat territories were reduced to ash. And federally threatened California red-legged frogs lost years of hard-won habitat and population gains.

Starting in 2014, biologists worked to reintroduce California red-legged frogs at four stream locations with nice, deep breeding pools within their former range. They translocated portions of egg masses laid by frogs in the nearby Simi Hills, and kept watch as the tadpoles hatched and grew into froglets. As hoped, the frogs survived to adulthood in sufficient numbers to breed on their own in their new homes. They were doing great.

Adult California red-legged frogs spend most of their time on land where they eat insects and other invertebrates among the vegetation. It’s possible, then, that hundreds of them died as the Woolsey Fire swept across the Santa Monica Mountains. All of their habitat burned around three of the four translocation streams. The fire did not stop there. The vegetation around the breeding pools in the Simi Hills was destroyed as well.

At the Simi Hills site, the deep breeding pools remained intact in spite of the fire and the subsequent heavy rains. Sedimentation was minimal because of the area’s gentler topography. At the relocation sites, all of the deep pools were completely filled in with debris.

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Remarkably, surveys right after the fire turned up lots of frogs on the scorched landscape around the Simi Hills pools. Biologists also found one frog at each of the burned translocation sites. One may not sound like much, but here, where there is one survivor, there are probably more.

The flames, however, were not the last of the frogs’ fire-related troubles. Without plants to anchor the soil, heavy winter rain storms filled the streams with huge amounts of ash, soil, and debris from the surrounding moonscape. All of the deep pools where the frogs could breed and find refuge were completely filled in with debris in the three hardest hit translocation streams.

Survey data reflected the devastation at the translocation sites. Biologists found no California red-legged frog egg masses in the now-too-shallow waters of the three hardest hit translocation streams. In the stream where some of the surrounding vegetation survived, biologists found just four egg masses where they had found 12 and 13 in 2017 and 2018. They aren’t exactly sure why. Adult frogs still may have been lost in the fire in the surrounding landscape, or high stream flows could have discouraged breeding. In addition, their breeding pools did shrink because of debris washing down from burned areas upstream.

Biologists were overjoyed to discover 84 egg masses at the Simi Hills site. They took 1,000 of these eggs to the Santa Barbara Zoo, raised them to their tadpole stage, and released them at two of the least devastated translocation sites to support their recovery.

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At the Simi Hills site, the deep breeding pools remained intact; sedimentation was minimal because of the area’s gentler topography. Nonetheless, biologists expected a dip in breeding related to the fire. Instead, they were overjoyed to discover 84 egg masses, a large number even for a normal year at the site! Biologists took 1,000 of these eggs to the Santa Barbara Zoo, raised them to their tadpole stage, and released them at two of the least devastated translocation sites to support their recovery.

Inspired by similar successful projects elsewhere, a team of agencies also plan to dig out debris from the former pools at two or more of the hardest hit translocation sites in time for the fall. Having access to pools is key for the frogs to find refuge during the warmest, driest months of the year.

From there, biologists plan to keep tabs on the pools and the frogs monthly. What they find will help determine their next course of action for supporting red-legged frog recovery in the Santa Monica Mountains. Nighttime surveys in the fall will be especially useful for getting a better sense of how many adult frogs actually survived the Woolsey Fire. If the re-created pools remain deep enough to serve as breeding pools after next winter’s rains, more translocations from the amazingly resilient Simi Hills population could be on the table next spring.

UPDATE 10/15/2019: Fall night surveys revealed 28 adult frogs across the four translocation sites!

Partners in the reintroduction project are California State Parks, the Mountains Recreation and Conservation Authority, the Santa Barbara Zoo, California State Coastal Conservancy, Santa Monica Bay Restoration Commission, the Santa Monica Mountains Conservancy, the U.S. Fish and Wildlife Service and the U.S. Geological Survey (USGS).

Science by the Sea newsletter article by the Mediterranean Coast Inventory and Monitoring Network.