Some Frogs Climb Waterfalls

In the mountain yellow-legged frog lab, we recently wrapped up our field season for this year, including the post-reintroduction surveys for the 111 froglets we released in May at Dark Canyon in the San Jacinto Mountains of California. Across eight surveys spread from June to October, we were very excited to locate 38 uniquely identified froglets from the release cohort and gather data on their growth and movements since release. Much to our surprise, some frogs made incredible journeys.

Adult mountain yellow-legged frogs tend to have high site fidelity, being found in the same pools or small stretch of creek year after year, so the vast majority of dispersal movement is thought to occur when the frogs are young. Released at only 1.5-2 inches in length, the average distance the frogs traveled from their release pools was 121 meters (roughly 400 feet). Some frogs were happy to stay close to their release pool, being recaptured only 10-20 meters away, while others dispersed to distant pools in the creek, hopping and swimming along for hundreds of meters. The record distances traveled this year were by two female frogs found 630 and 710 meters upstream!

These distances alone would be impressive, but the terrain traversed only adds to the intrigue. These two little frogs navigated areas with large boulders and fallen trees, travelled over portions of the creek that had dried up in the summer heat, and gained more than 200 feet in elevation as they sought out a pool to call home. Upstream of the release pools is a 50-foot waterfall of large granite stones, with a gentle trickle of water flowing down it. In releasing the frogs downstream of the waterfall, we had assumed this natural obstacle would prevent the frogs from moving upstream, allowing us to establish a separate release cohort upstream of the waterfall. The frogs of course had different plans, not only climbing the waterfall but continuing upstream for 300 meters past it! While making this journey, these two frogs had been busy eating too, as both had more than doubled in weight and had increased in body length by 3/4 inch, giving them similar growth rates as their less adventurous siblings downstream.

Hopefully next year we’ll be able to recapture these two frogs again to see if they continued their journey or if they settled where they were found this year.