Timing is probably to ensure that water is cool enough for embryonic survival and that sufficient water exists for larval growth to metamorphosis. Egg masses are typically attached to emergent vegetation with a vertical orientation. Nussbaum et al. Dam construction , which destroys suitable habitat and fragments remaining habitat, results in isolated populations. Reservoirs act as barriers because they are unsuitable frog habitat and they are suitable habitat for introduced aquatic predators.
Cattle can destroy crucial riparian vegetation, especially in drought years.
The small coastal drainages between Point Reyes National Seashore in Marin County and Carpenteria in Santa Barbara County are the only remaining areas with significant numbers of California red-legged frogs. There are currently only three known California red-legged frog populations with greater than 350 adults, all near the coast in the San Francisco Bay Region. Jennings et al. Greater than 25 percent of riparian area thickly vegetated. Greater than 25 percent of pool area thickly vegetated with cattails, bullrushes or other emergent vegetation.