Breeding occurs between March and July in mountainous areas, and as early as January in lower-elevation regions.

The female lays up to 17,000 eggs stuck together in strings that adhere to vegetation and other objects along water edges.

[8] Southern records of boreal toads in New Mexico have been published,[9] but the species is considered extirpated from the state, with a reintroduction in progress.

[10] In Colorado, the largest populations are typically found in areas characterized by willows (Salix spp.

[11] In the Pacific Northwest, the western toad occurs in mountain meadows and less commonly in Douglas-fir forests (Pseudotsuga menziesii).

[10] In California, optimum habitat for the western toad includes wet or dry mountain meadows or riparian deciduous forest with available open water for breeding.

Suitable habitat includes blue oak (Quercus douglasii) savanna, gray pine-oak forest (Pinus sabiniana-Quercus spp.

[12] In the Sierra Nevada, the western toad occurs in mid-elevation pine forests (including Jeffrey pine (Pinus jeffreyi) at higher elevations and ponderosa pine (Pinus ponderosa) at lower elevations), California black oak woodlands (Quercus kelloggii), giant sequoia groves (Sequoiadendron giganteum), montane fir forest (which includes white fir (Abies concolor), red fir (Abies magnifica), and western white pine (Pinus monticola), and redwood forest (Sequoia sempervirens).

[10] Western toads have been collected from sedge meadows near a pond occurring in a creosotebush (Larrea tridentata) community, and from aspen (Populus spp.

The high water table, constantly flowing stream, and deep winter snow served to maintain the air temperature within the hibernaculum at a point slightly above freezing.

[11] Eggs are laid in open water from February to July, with peak activity occurring in April.

[19] Western toads occupy desert streams and springs, grasslands, and mountain meadows; they are less common in heavily wooded regions.

[16] In Colorado, individual western toads typically maintain distinct ranges which vary greatly in size according to the condition of the habitat.

For example, at one site on a permanent lake in the Oregon Cascade Range, western toads returned each year to the same submerged willow clumps.

In order to avoid evaporative conditions, they usually spend the daylight hours on the forest floor in the soil under rocks, logs, stumps, or other surface objects or in rodent burrows.

[16] Western toads lay their eggs in water; they require some form of surface cover near the egg-laying location.

[10] Adult western toads are preyed upon by common ravens (Corvus corax) and probably by other birds, reptiles, amphibians, and mammals as well.

One of the chief chemical threats is the overuse of urea as fertilizer, which is often applied in high dosage to forest environments to increase biomass productivity and economic return.