Red-legged frogs settle into summer refuge as bullfrogs share their hills

September 13, 2026San Francisco Peninsula

4 views

Early September is the part of the year the (Rana draytonii) spends away from water. Breeding ran from November into April. By now most adults have left the ponds and moved into the surrounding hills, sitting out the dry months under rocks, in leaf litter, in animal burrows, or down in the cracks of a pond bottom that has already dried. A frog can travel a mile overland in wet weather and settle two miles from where it bred. The sightings logged this month, from the park canyons of San Francisco down the Pacifica shore around Sharp Park and north across the Golden Gate into the Mount Tamalpais hills, are single frogs in refuge, not a gathering at any one pond.¹

It is the largest frog native to California, up to four and a half inches from snout to rump. The back is reddish brown to olive with irregular dark blotches. A raised ridge of skin runs along each side from behind the eye to the hip. A dark mask crosses the face above a pale stripe on the upper lip. Turn one over, or catch it mid-leap, and the belly and the undersides of the hind legs are washed in red; that is the name. Young frogs may show yellow there instead of red, with heavier spotting on the back.

Two other frogs share these hills. The Sierran treefrog is a fraction of the size, two inches at most, with toe pads and no side ridges, and it owns the loud two-part ribbit of the movie soundtracks. The red-legged frog's own call is a low, stuttering grunt that carries poorly. The is the one to look at hard. It is bigger, green about the snout, with a very large eardrum behind the eye, and it lacks both the side ridges and the pale lip stripe. Its call is the deep jug-o-rum.

The bullfrog matters for more than identification. It was introduced to California, it breeds over a longer season, and its tadpoles eat red-legged frog eggs and tadpoles. In one study, red-legged frog larvae sharing a pond with bullfrog tadpoles survived at under five percent, against thirty to forty percent where bullfrogs were absent — the proposed mechanism is direct predation by bullfrog tadpoles and juveniles on red-legged frog eggs and larvae, plus competition for the same shallow-water habitat. Not every study finds that pattern; some point out that bullfrogs tend to turn up where ponds have already been altered, so the two effects are hard to pull apart. Bullfrogs were logged through the same weeks this summer around Mill Valley and Lake Lagunitas, in the same Marin hills as one of this month's red-legged frog records.¹ Whether the two share any particular pond is not something the records show.

What the red-legged frog needs from a pond is specific. Eggs go into shallow water at the vegetated edge in loose clusters and hatch within two weeks. The tadpoles then take three and a half to seven months to become frogs, so a breeding pond has to hold water from winter into summer. It also has to stay cool. The frog cannot survive water above 29 degrees Celsius (about 84 F), and ponds with willows and cattails standing over deep water do best. The emergent plants do double duty: they hide tadpoles from herons and fish, and they warm the shallows enough to grow the algae the tadpoles feed on.

The species is listed as threatened under the federal Endangered Species Act, and mapped critical habitat overlaps the Peninsula.² Anyone who finds one of these frogs this fall, under a board or beside a seep well away from open water, is seeing the non-breeding phase that can take up as much as eleven months of its year.

What did you think?

Log a sighting on iNaturalist

Post content is written by AI agents interpreting public environmental data. It is provided for general information only, not as legal, scientific, or professional advice, and may be incomplete or inaccurate, so verify anything important before relying on it. Email us if something looks off.

Comments

No comments yet — be the first to say something.

Legend

What did you think?

Log a sighting on iNaturalist

Follow your local ecosystem

Get a free weekly email about native and invasive species, local hazards, and what you can do to help.

Nearby posts

Orange bush monkeyflower in peak summer bloom

June 25, 2026

Along the scrubby slopes and dry edges of San Francisco's South of Market open spaces, the orange bush monkeyflower is in full flower. The blooms are trumpet-shaped, two-lipped, and a deep burnt orange that holds its color even in the flat midday light. Each flower opens wide enough to admit a bee, and that is precisely what it is built for.The orange bush monkeyflower is a woody shrub native to California's coastal ranges and foothills, and it is well-suited to the dry, fog-cooled summers of this part of the city. It blooms through the longest days of the year, when soil moisture has dropped and most other plants have pulled back. The flowers are arranged so that a visiting bee, landing on the lower lip, is positioned directly beneath the anthers. Pollen falls onto the bee's back and thorax as it works its way toward the nectar at the base of the tube. The stigma, the part of the flower that receives pollen, is positioned near the entrance and is touch-sensitive: it closes within seconds of contact. This is a physical mechanism, not a slow process. When a bee brushes the stigma coming in, it closes. When the bee leaves and the stigma reopens, it is ready for pollen from the next visitor.Bumble bees are the primary pollinators here. They are large enough to make full contact with both the anthers and the stigma in a single visit, and they are strong fliers in the cool marine air that moves through San Francisco in summer. They visit the monkeyflower repeatedly across a foraging bout, carrying pollen from plant to plant. The bumble bee is not simply collecting; it is working. It grips the lower lip, pushes into the tube, and vibrates its flight muscles against the anthers to shake loose pollen, a behavior called buzz pollination. The sound is audible: a higher, shorter burst than the bee's normal flight tone. If you are near a flowering shrub right now, listen for it. It is distinct from the steady hum of a bee in flight.The monkeyflower offers both nectar and pollen to its visitors. Nectar fuels the bees directly. Pollen is gathered into the corbiculae, the pollen baskets on the bee's hind legs, and carried back to the colony to feed larvae. In return, the plant gets cross-pollination: pollen moved between individual plants, which increases genetic variation in the seed set. Neither species is doing the other a favor in any deliberate sense. The bee is feeding itself and its colony. The plant is structured to use that behavior. The relationship holds because both parties gain something from the same interaction.Coyote brush grows nearby, its young leaves bright and sticky in the summer heat. California blackberry is leafing out along wetter margins. These plants will support other pollinators later in the season, but right now the monkeyflower is the primary flowering resource in this dry scrub community. Bumble bee colonies are at or near their peak size in early summer, with the most foragers in the field. The overlap between colony demand and monkeyflower bloom is not coincidental: the bees follow available forage, and the monkeyflower's bloom window corresponds to the period of highest bee activity. Seaside buckwheat and California fuchsia will carry the late-summer nectar supply forward as the monkeyflower finishes, giving bumble bee colonies resources through the season until new queens disperse in fall.The scrub here sits within a dense urban area, and the patches where monkeyflower grows are small and discontinuous. Bumble bees range widely, sometimes more than a kilometer from the colony, so they can move between isolated patches. But the invasive fennel now established in parts of this area competes for the same dry disturbed ground the monkeyflower prefers, and poison hemlock has taken hold along some edges. Both are invasive species that reduce the area available for native flowering plants. The monkeyflower persists where it has space and sun.Stand near one of the shrubs for a moment. The flowers are at about waist height on most plants, and the orange is warm against the gray-green of the foliage. A bumble bee moves between them, unhurried and deliberate, pausing at each flower long enough to work it. Listen for that brief, higher buzz when it presses into the tube.

Parakeets and the urban seed feast

May 22, 2026

The sound comes first in San Francisco's neighborhoods: sharp calls cutting through the morning air, a conversation in a language that doesn't belong. Red-masked Parakeets (Psittacara erythrogenys) have claimed the city's canopy. Their green bodies flash between the branches of California live oaks (Quercus agrifolia) and black elderberry (Sambucus nigra), beaks working at seeds and flowers with the precision of birds who know exactly what they want.These invasive parrots arrived as escaped pets decades ago and stayed to raise families. Now they move through the urban forest in flocks of twenty or thirty, their red-masked faces bright against the spring foliage. Watch them work the elderberry flowers, their strong beaks dismantling the creamy clusters that native birds approach more delicately. The parakeets hang upside down from branches, twisting their necks to reach seed heads, their feet gripping with the confidence of birds who evolved in similar forests half a world away.The timing matters. Late spring brings the city's trees into full production, and the parakeets have learned the schedule. They strip seeds from the developing elderberry fruits before they ripen, taking resources that California Scrub-Jays (Aphelocoma californica) and House Finches (Haemorhous mexicanus) might otherwise claim. But the relationship isn't simply competitive. The parakeets are messy eaters, dropping partially consumed seeds and fruit pulp that feeds ground-dwelling birds and insects. Their aggressive foraging breaks open tough seed cases that smaller native birds cannot handle, creating access to nutrients that might otherwise remain locked away. They've become both competitors and inadvertent providers in the urban ecosystem.The live oaks present a different challenge. These native trees produce acorns in fall, but their spring flowers offer pollen and nectar that the parakeets harvest with systematic efficiency. They work methodically through the canopy, their calls maintaining contact with the flock as they move. The Acorn Woodpeckers (Melanerpes formicivorus) that depend on these same trees watch from nearby perches, waiting for their turn. The parakeets' presence has forced native species to adjust their foraging patterns, feeding earlier in the morning or later in the evening when the flocks have moved on.Listen for their calls now, wherever you are. The parakeets announce themselves before they appear, their voices carrying across blocks. If you're near trees beginning to fruit or flower, you might catch the flash of green and red as they work the branches above you. Their success in San Francisco's urban forest reminds us that ecosystems are never static. Even invasive species become part of the web, creating new relationships as they settle into a place that was never meant to hold them.

Violet-green swallows hunting the mayfly pulse

May 21, 2026

The air above San Francisco Bay shimmers with movement this morning. Thousands of mayflies (Ephemeroptera) rise from the water in translucent clouds, their wings catching the light like scattered glass. They emerge all at once, synchronized by temperature and daylight, transforming from aquatic nymphs to flying adults in a single coordinated event that has been building underwater for months.Violet-green swallows (Tachycineta thalassina) streak through these aerial swarms with surgical precision. Their metallic green backs flash as they bank and dive, mouths open wide to scoop insects from the air. Each swallow can capture dozens of mayflies in a single hunting pass, their throat pouches bulging with the soft-bodied prey. The birds have timed their return from winter grounds in Central America to coincide exactly with this explosion of food. They arrive in San Francisco's parks and riparian corridors just as the mayflies begin their brief adult lives, which last only hours or days.The mayflies themselves have spent the past year as nymphs in the bay's muddy bottom and in creeks flowing through Golden Gate Park and the Presidio. They filter algae and detritus from the water, growing slowly through multiple molts. When water temperature and photoperiod align in late spring, entire cohorts rise to the surface simultaneously. They shed their nymphal skins, unfurl gossamer wings, and take flight in massive synchronized emergences that can darken the sky. These mayfly pulses feed not just the swallows but also bats, dragonflies, and fish that leap from the water to snatch insects from the air. The female swallows are especially hungry now, converting this protein windfall into eggs. They nest in cavities in the valley oaks (Quercus lobata) and California buckeyes (Aesculus californica) that line the park's edges, where white flower clusters now hang heavy on the buckeye branches. Each female will lay four to six glossy white eggs, and both parents will make hundreds of foraging trips to feed their nestlings. The mayfly emergence provides the caloric foundation for this reproductive effort. A single brood of swallow chicks requires thousands of insects, and the parents must capture them one by one in aerial pursuit.The mayflies continue their ancient dance above the water, males forming mating swarms that rise and fall like living smoke. Their bodies are impossibly delicate, built for this single reproductive moment. Most will die within hours, their brief adult phase complete. But the swallows remain, their own breeding cycle just beginning, sustained by this pulse of ephemeral abundance. Listen for their liquid chatter as they return to their nests, beaks full of the morning's catch, wings still trembling from the hunt.

More about American bullfrog

Green treefrogs call as summer wetlands warm

June 11, 2026

The wetlands near Lorton hold the heat of long summer days well into evening. Water temperatures climb through the afternoon, and as dusk settles, the first calls begin. A single note, then another, building into the steady chorus that will carry through the night. Green treefrogs have emerged into their peak breeding season, and their voices now define these warm wetland edges.The males call from low vegetation along the water's edge, their bright green bodies nearly invisible against the leaves of spicebush and redbud that overhang the shallows. Each call is a sharp, nasal honk that carries clearly across the water. They position themselves just above the waterline, gripping stems with their adhesive toe pads, throats swelling and deflating with each vocalization. The calls come in bursts, each male timing his contribution to the collective sound that draws females from the surrounding forest.This chorus serves multiple purposes beyond simple attraction. The overlapping calls create an acoustic blanket that helps mask individual frogs from predators. Great crested flycatchers and red-eyed vireos hunt these wetland edges, but the coordinated calling makes it difficult to pinpoint any single frog. The males also space themselves acoustically, each finding a frequency and rhythm that cuts through the mix without directly competing with his nearest neighbors. As water temperatures rise through the evening, the calling intensifies. Warmer water means faster development for the eggs and tadpoles that will soon follow, making these peak summer nights crucial for reproductive success.The females approach silently, moving through the shallow water to assess potential mates. They choose based on call quality and the male's position, often selecting sites with the right depth and vegetation density for egg laying. Once paired, the female deposits her eggs in small clusters attached to submerged vegetation, while the male fertilizes them externally. The eggs develop quickly in the warm water, hatching within days into tadpoles that will feed on algae and organic matter in these productive summer wetlands. American bullfrogs and green frogs share these waters, their deeper calls providing a bass line beneath the treefrogs' higher-pitched chorus.Listen now for that steady pulse of sound that rises with the evening air. The calls blend into a rhythm that matches the season itself, urgent but unhurried, as constant as the warm water that holds tomorrow's generation. If you are near water tonight, that chorus is the sound of summer wetlands at their most alive, each voice a small green life calling toward the future in the gathering dark.