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10 August 2016 Discovery of the Oregon Spotted Frog in the Northern Puget Sound Basin, Washington State
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Abstract

The Oregon Spotted Frog (Rana pretiosa), a federally threatened species also listed as endangered in Washington State, has a historical distribution that extends from southwestern British Columbia to northeastern California, yet their current range appears highly fragmented. This pattern may reflect this species' distinctive aquatic habitat requirements or simply be a function of the limited historical survey effort in selected areas. Hence, in an attempt to determine whether any additional populations of Oregon Spotted Frogs existed in the northern Puget Sound basin of Washington State, we conducted surveys at a large number of sites (n = 131) across this region in 2011–2013. To increase the likelihood of detecting this species, we created a Geographic Information System screening tool to identify areas of appropriate habitat (low stature emergent marsh ≥4 ha) based on National Wetlands Inventory maps. We also concentrated survey efforts on the headwater portions of lowland streams because non-headwater areas within the study area are highly altered and more likely to harbor exotic aquatic predators (American Bullfrogs [Lithobates catesbeianus] and warmwater fish species), which reduce the likelihood of Oregon Spotted Frog occupancy. We visually documented breeding activity of Oregon Spotted Frogs at 13 previously unrecognized sites in the Samish (n = 8), Nooksack (n = 4), and Sumas (n = 1) watersheds. We located a total of 1359 Oregon Spotted Frog egg masses at the 13 occupied sites over the three survey seasons. We genetically verified the species identification at 4 of these sites. In the course of these surveys, we also documented breeding chronology and provided information on habitat. Vegetation changes due to cessation of grazing and recent woody plantings may have decreased habitat suitability in at least 5 of the 13 occupied sites. Despite time and land-ownership constraints, our discovery of new breeding sites suggests that additional surveys for Oregon Spotted Frogs are needed to fully understand the species' distribution. Although Oregon Spotted Frogs are still rare, their current distribution is more widespread than previously recognized.

Jennifer S Bohannon, Don R Gay, Marc P Hayes, Christopher D Danilson, and Kenneth I Warheit "Discovery of the Oregon Spotted Frog in the Northern Puget Sound Basin, Washington State," Northwestern Naturalist 97(2), 82-97, (10 August 2016). https://doi.org/10.1898/NWN15-19.1
Received: 29 April 2015; Accepted: 8 December 2015; Published: 10 August 2016
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