James W. Watson, Kelly R. McAllister, D. John Pierce
Journal of Herpetology 37 (2), 292-300, (1 April 2003) https://doi.org/10.1670/0022-1511(2003)037[0292:HRMAHS]2.0.CO;2
From 1997–1999 we studied one of four known populations of Oregon Spotted Frogs (Rana pretiosa) in Washington State to investigate patterns of range use, movements, and habitat selection. Sixty telemetered frogs occupied a range that was a mosaic of wetlands (15.6 ha) and upland pasture (13.2 ha) grazed by dairy cows. Mean (± SE) home-range size for four frogs was 2.2 ± 1.0 ha. Patterns of spatial use, determined from 654 telemetry locations, were closely related to season and changing surface water conditions. During the breeding season (February to May), frogs occupied ≥50% of the area they used the entire year, and oviposited in shallow pools (depth = 16.9 ± 0.6 cm) on the margins of an ephemeral creek. In the dry season (June to August), frogs moved down stream to deeper, permanent pools (depth = 23.6 ± 1.0 cm), significantly reduced their movements, and occupied the smallest ranges of any season. During the wet season (September to January), frogs moved back up stream and reoccupied the breeding range. During the coldest weather, frogs buried themselves at the base of dense vegetation in shallow water under ice (depth = 17.4 ± 0.8 cm). Frogs avoided dry uplands. Frogs selected sedge (Carex obnupta, and Carex utriculata)/rush (Juncus effusus) habitat during breeding and hardhack (Spiraea douglasii) cover during the dry season that shaded and maintained remnant pools. Frogs preferred microhabitats with 50–75% water surface exposure based on comparisons between telemetry locations and nearby locations that were randomly selected. Aquatic requirements necessary to complete the life cycle of Oregon Spotted Frogs in this population include (1) stable, shallow water areas for egg and tadpole survival in the breeding season, (2) deep, moderately vegetated pools for adult and juvenile survival in the dry season, and (3) shallow water levels over emergent vegetation for protecting all age classes during cold weather in the wet season.