The California red-legged frog is listed as threatened under the Endangered Species Act. It once ranged from Marin County, California, to Baja California, Mexico, but its range has shrunk to 30% of its former size because of overharvesting in the 1800s, habitat loss and invasive species such as bullfrogs. The National Park Service and partners have restored habitat and monitored the frogs across Golden Gate National Recreation Area, Point Reyes National Seashore and Sharp Park.
A pair of red-legged frogs in amplexus, the mating embrace in which the male clings to the female. NPS / Aiko Goldston.
Counting eggs, not frogs
The frogs themselves are hard to count, but their egg masses — about the size of a grapefruit and laid near the water's surface — are much easier. Surveys cover the breeding season from December to March, sometimes by kayak.
A California red-legged frog egg mass. NPS / Matt Millado.
2023 results
| Breeding season | Egg masses found |
|---|---|
| 2021 | 496 |
| 2022 | 491 |
| 2023 (December 2022–March 2023) | 348, at 37 sites in Marin and San Mateo counties |
| County | What changed from 2022 to 2023 |
|---|---|
| Marin | Counts generally fell, with sharp drops at Tennessee Valley and Rodeo Lagoon; Bolinas Lagoon was the exception |
| San Mateo | Counts generally rose, including at Laguna Salada and Sharp Park — but Milagra Ridge, a seasonal wetland whose frogs may have suffered from consecutive drought years, had none |
Egg masses counted each breeding season in Marin County watersheds, 2001–2023. Image from the National Park Service's article on 2023 red-legged frog breeding surveys.
Egg masses counted each breeding season in San Mateo County watersheds, 2001–2023. Image from the National Park Service's article on 2023 red-legged frog breeding surveys.
The drop may partly reflect gaps in surveys: several large storms brought so much rain that visibility suffered and some surveys couldn't happen, possibly leading to fewer egg masses being recorded.
The long view
Since monitoring began in the early 2000s, red-legged frog populations appear to be improving overall, thanks in part to park work to reconnect water flow within watersheds, build new breeding ponds and manage invasive species. Park biologists will keep monitoring the frogs.
Surveying by kayak. NPS / Matt Millado.
Sources
Based on "2023 California Red-legged Frog Breeding Surveys Yield Mixed Results," by aquatics intern Matt Millado, Golden Gate National Recreation Area, published by the National Park Service; rewritten in hubnx's own words.
In these publicationsGolden Gate National Recreation Area
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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