Reproduction
Males and females begin to move to the breeding sites as early as October, and sometimes as late as January, depending on latitude, cumulative rainfall for the season, and average temperature. Typically, stable minimum temperatures of 42 to 44°F are required to induce breeding. Observations of adult migration are best made on moonlit nights with light rains. The male is thought to defend his territory, once he is in the breeding pond area, using nocturnal displays. In fact, most activity is at night, especially enhanced by periods of light rain. The actual courtship behaviors commence in January in the California part of the range, and as late as March in northerly regions. In any case, the breeding season terminates in July at the latest, and earlier in the drier locales.Each female produces 200 to 1100 eggs per season, and attaches the egg cluster to submerged vegetation or rotting logs, characteristically seven to 15 cm below the pond surface. Egg clusters are typically about 10 cm in diameter, and may disperse into an irregular form underwater. Eggs hatch in 39 to 45 days, and tadpoles require about 80 days to attain metamorphosis.
Oviposition generally takes place in densely vegetated, shallow portions of wetlands with little current, and in unusual cases, egg masses have been observed in water up to 500 cm in depth. Breeding sites can be either permanent or temporary, with inundation usually necessary into June for successful metamorphosis. The June date is based on Oregon conditions; in Northern California, metamorphosis occurs in late May or early June. Breeding is initiated when water temperatures exceed about 6°C , but can be as late as March in the extreme northern part of the range.
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