Anaxyrus boreas - (Baird and Girard, 1852)
Western Toad
Other English Common Names: western toad
Other Common Names: Boreal Toad
Synonym(s): Bufo boreas Baird and Girard, 1852
Taxonomic Status: Accepted
Related ITIS Name(s): Anaxyrus boreas (Baird and Girard, 1852) (TSN 773513)
French Common Names: crapaud de l'Ouest
Unique Identifier: ELEMENT_GLOBAL.2.102714
Element Code: AAABB01030
Informal Taxonomy: Animals, Vertebrates - Amphibians - Frogs and Toads
Image 10659

© Dick Cannings

 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Amphibia Anura Bufonidae Anaxyrus
Genus Size: D - Medium to large genus (21+ species)
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Concept Reference
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Concept Reference: Frost, D. R. 1985. Amphibian species of the world. A taxonomic and geographical reference. Allen Press, Inc., and The Association of Systematics Collections, Lawrence, Kansas. v + 732 pp.
Concept Reference Code: B85FRO01HQUS
Name Used in Concept Reference: Bufo boreas
Taxonomic Comments: The genus Anaxyrus was split from Bufo by Frost et al. (2006). However, taxonomy within the genus Bufo remains controversial and many references still use the long-established Bufo. The two remaining subspecies (Anaxyrus boreas boreas and Anaxyrus boreas halophilus) are still recognized by some authors, but these are physiologically strongly divergent and there may be cryptic species masquerading under this binominal (Frost 2017).

Bufo (Anaxyrus) boreas is closely related to Bufo (Anaxyrus) canorus and Bufo (Anaxyrus) exsul. "Stephens (2001) examined mitochondrial DNA from 8 Yosemite toads (selected from the samples examined by Shaffer et al. (2000) to represent the range of variability found in that study) and 173 western toads. Stephens' data indicate that Bufo in the Sierra Nevada occur in northern and southern evolutionary groups, each of which include both Yosemite and western toads (i.e., toads of both species are more closely related to each other within a group than they are to members of their own species in the other group). Further genetic analysis of Yosemite toads sampled from throughout their range, and from other toad species surrounding their range is needed to fully understand the evolutionary history and appropriate taxonomic status of the Yosemite toad (Stephens 2001)." (USFWS 2002).

Molecular data indicate that exsul is phylogenetically nested within canorus; further data are needed to determine whether exsul should be subsumed with canorus (Shaffer et al. 2000).

The subspecies of Bufo (Anaxyrus) boreas, as traditionally defined (e.g., Stebbins 2003), appear to be not valid as distinct evolutionary lineages. The ranges of these subspecies (boreas, halophilus) do not correspond very well with geographic patterns of mtDNA variation as found by Goebel et al. (2009). The geographic distribution of the haplotype clade that includes most of the traditionally recognized range of boreas includes not only the type locality of boreas but also that of subspecies halophilus (Goebel et al. 2009).

Phylogenetic analyses of mtDNA data from throughout the range of the Bufo (Anaxyrus) boreas species group (including boreas, canorus, exsul, and nelsoni) by Goebel et al. (2009) identified three major haplotype clades. The Northwest clade (NW) includes both subspecies of boreas (boreas and halophilus) and divergent minor clades in the middle Rocky Mountains, coastal, and central regions of the west, and Pacific Northwest. The Southwest (SW) clade includes exsul, nelsoni, and minor clades in southern California. Bufo (Anaxyrus) canorus, previously identified as paraphyletic, has populations in both the NW and SW major clades. The Eastern major clade (E) includes three divergent lineages from southern Utah, the southern Rocky Mountains, and north of the Great Basin at the border of Utah and Nevada. Goebel et al. (2009) tentatively suggested that some or many of the clades might warrant recognition as distinct species. However, the authors refrained from delineating new species circumscriptions, noting that additional research might suggest different taxonomic outcomes (e.g., recognizing the traditionally defined Bufo canorus as two distinct species or, conversely, combining it with other minor groups and thus broadening its scope).
Conservation Status
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NatureServe Status

Global Status: G4
Global Status Last Reviewed: 03Jan2008
Global Status Last Changed: 15Oct2001
Rounded Global Status: G4 - Apparently Secure
Reasons: Large range in much of the western United States and western Canada; locally common, but rapid losses and declines have occurred in many populations across the range for unknown reasons, even in relatively pristine environments.
Nation: United States
National Status: N4 (05Nov1996)
Nation: Canada
National Status: N3N4 (20Mar2017)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alaska (S3S4), California (SNR), Colorado (S1), Idaho (S2), Montana (S2), Nevada (S4), New Mexico (S1), Oregon (S4), Utah (S3), Washington (S3), Wyoming (S1)
Canada Alberta (S3S4), British Columbia (S4), Northwest Territories (S2S3), Yukon Territory (S3)

Other Statuses

Canadian Species at Risk Act (SARA) Schedule 1/Annexe 1 Status: SC (12Jan2005)
Implied Status under the Committee on the Status of Endangered Wildlife in Canada (COSEWIC):PS: SC
Comments on COSEWIC: The species was considered a single unit and designated Special Concern in November 2012. Split into two populations in November 2012.
IUCN Red List Category: NT - Near threatened

NatureServe Global Conservation Status Factors

Range Extent: 200,000 to >2,500,000 square km (about 80,000 to >1,000,000 square miles)
Range Extent Comments: The range extends along the Pacific Coast from southern Alaska (Wiedmer and Hodge 1996) to Baja California, and eastward through the Rocky Mountains to west-central Alberta, Montana (Werner et al. 2004), Wyoming (Baxter and Stone 1985), Utah (Ross et al. 1995, Thompson et al. 2004), Colorado (Hammerson 1999), and (formerly) northern New Mexico (Degenhardt et al. 1996). The species is absent from most of the desert Southwest (Stebbins 2003). Elevational range extends from sea level to more than 11,000 feet (3.355 meters) in some areas in the Rocky Mountains.

Number of Occurrences: 81 to >300
Number of Occurrences Comments: Represented by many and/or large occurrences throughout most of the range.

Population Size: 100,000 - 1,000,000 individuals
Population Size Comments: Total adult population size is unknown but likely exceeds 100,000. Still common in much of the range.

Overall Threat Impact: Medium
Overall Threat Impact Comments: The extent of threats range-wide is not known with certainty, but there appear to be multiple causes contributing to the range-wide trend.

Disease and parasites appear to be contributing factors leading to population declines. Carey (1993) hypothesized that some environmental factor or synergistic effects of more than one factor may stress toads, causing suppression of the immune system or indirectly causing immunosuppression by effecting elevated secretion of adrenal cortical hormones. Immunosuppression, coupled with the apparent effect of cold body temperatures on the ability of the immune system to fight disease, may lead to infection by Aeromonas hydrophila bacteria (which causes "red-leg") or other infectious agents and subsequently to death of individuals and extirpation of populations. Die-offs in the Southern Rockies have been associated with chytrid fungus (Batrachochytrium dendrobatidis) infections (Daszak et al. 2000), which attacks keratinized tissue and is especially detrimental to recently metamorphed toadlets. Also, toad eggs are highly susceptible to the pathogenic fungus Saprolegnia ferax (which may be introduced during fish stocking), and mortality of eggs due to this fungus has been documented in Oregon (Blaustein et al. 1994; Kiesecker and Blaustein 1997; Kiesecker et al. 2001). Kiesecker et al. (2001) observed catastrophic embryo mortality from S. ferax infection in shallow water that was protected from UV-B but not in water protected from UV-B.

Limb malformations in toads have been linked directly to trematode infections by Ribeiroia ondatrae (Johnson et al. 2001; Johnson et al 2002), although the impacts of these infections on reproduction, and the magnitude of the infections across the breeding range, require further study. Preliminary analysis suggests that limb malformations may increase mortality in larval amphibians prior to and during metamorphosis.

Some have proposed that declines are related to sensitivity of eggs to increased levels of ultraviolet radiation (Blaustein et al. 1994), but studies by Corn (1998) yielded no support for UV-B alone as the cause of declines. Also, spectral characteristics of natural waters likely shield eggs from detrimental physiological effects in all but the clearest waters (Palen et al. 2002). Corn and Muths (2002) proposed that temperature stress is as plausible a hypothesis as increased UV-B to explain episodes of high mortality observed in Oregon (Kiesecker et al. 2001).

Increased acid deposition in natural habitats is a potential threat to amphibians, but this does not appear to be a major threat to Bufo boreas. For example, declines in the Southern Rocky Mountains are not due to acidification of breeding habitats (Corn and Vertucci 1992).

In the Cascade Range of Oregon, persistent predation on adult toads by Common Ravens during the breeding season appears to have contributed significantly to declines of some populations (Olson 1992). Possible significant predation by birds also has been observed in Colorado and Idaho (Hammerson 1999).

Declines may be related at least in part to habitat destruction and degradation, water retention projects, predation by and competition with native and non-native species, fishery management activities, or other factors, but these factors have not been adequately assessed. In Idaho, several hundred toadlets were trampled when domestic sheep were herded through the dried breeding pond (Bartelt 1998).

Short-term Trend: Decline of 10-30%
Short-term Trend Comments: This species is not threatened or declining in most of British Columbia or Alberta (see Green 1997), although Davis and Gregory (2003) documented a local extirpation at a relatively undisturbed site on southern Vancouver Island, British Columbia; they also noted an overall decline on Vancouver Island. Rocky Mountain populations in Colorado and Wyoming have undergone a drastic decline since the 1970s (Corn et al. 1989; Hammerson 1989, 1992, 1999; Carey 1993). Similarly, populations have declined greatly in the Yosemite area of the Sierra Nevada, California (Drost and Fellers 1996). Additionally, the species is apparently declining in Yellowstone National Park (Peterson et al. 1992), Montana (Reichel and Flath 1995), and locally elsewhere (Olson 1989).

Long-term Trend: Decline of <50% to Relatively Stable
Long-term Trend Comments: Likely relatively stable in extent of occurrence, unknown degree of decline in population size, area of occupancy, and number/condition of occurrences.

Intrinsic Vulnerability: Moderately vulnerable

Environmental Specificity: Moderate to broad.

Other NatureServe Conservation Status Information

Inventory Needs: Many museum records are not specific enough for resurveying. Precise locations of breeding sites are needed for long-term monitoring.

Protection Needs: Protection needs depend on causes of decline. At present in the Southern Rockies, efforts are being made to reduce the probability of chytrid fungus contamination of currently fingus-free breeding areas.

Distribution
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Global Range: (200,000 to >2,500,000 square km (about 80,000 to >1,000,000 square miles)) The range extends along the Pacific Coast from southern Alaska (Wiedmer and Hodge 1996) to Baja California, and eastward through the Rocky Mountains to west-central Alberta, Montana (Werner et al. 2004), Wyoming (Baxter and Stone 1985), Utah (Ross et al. 1995, Thompson et al. 2004), Colorado (Hammerson 1999), and (formerly) northern New Mexico (Degenhardt et al. 1996). The species is absent from most of the desert Southwest (Stebbins 2003). Elevational range extends from sea level to more than 11,000 feet (3.355 meters) in some areas in the Rocky Mountains.

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AK, CA, CO, ID, MT, NM, NV, OR, UT, WA, WY
Canada AB, BC, NT, YT

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted. For information on how to obtain shapefiles of species ranges see our Species Mapping pages at www.natureserve.org/conservation-tools/data-maps-tools.

Range Map Compilers: IUCN, Conservation International, NatureServe, and collaborators, 2004


U.S. Distribution by County Help
State County Name (FIPS Code)
AK Haines (02100), Juneau (02110), Ketchikan Gateway (02130), Prince of Wales-Outer Ketchikan (CA) (02201), Sitka (02220), Skagway-Hoonah-Angoon (CA) (02232), Wrangell-Petersburg (CA) (02280), Yakutat (02282)
ID Ada (16001)*, Adams (16003), Bannock (16005)*, Bear Lake (16007)*, Benewah (16009), Bingham (16011)*, Blaine (16013)*, Boise (16015)*, Bonner (16017), Bonneville (16019), Boundary (16021), Camas (16025), Caribou (16029), Cassia (16031), Clark (16033), Clearwater (16035), Custer (16037), Elmore (16039), Franklin (16041)*, Fremont (16043), Gooding (16047), Idaho (16049), Jerome (16053), Kootenai (16055), Latah (16057), Lemhi (16059), Lewis (16061), Nez Perce (16069), Owyhee (16073), Power (16077)*, Shoshone (16079), Twin Falls (16083), Valley (16085), Washington (16087)
MT Beaverhead (30001), Chouteau (30015)*, Deer Lodge (30023), Flathead (30029), Gallatin (30031), Glacier (30035), Granite (30039), Jefferson (30043), Judith Basin (30045), Lake (30047), Lewis and Clark (30049), Lincoln (30053), Madison (30057), Meagher (30059), Mineral (30061), Missoula (30063), Park (30067), Pondera (30073), Powell (30077), Ravalli (30081), Sanders (30089), Silver Bow (30093), Teton (30099)
NM Rio Arriba (35039)
NV Mineral (32021)*
OR Baker (41001), Crook (41013), Curry (41015)*, Deschutes (41017), Gilliam (41021), Grant (41023), Harney (41025), Jackson (41029), Jefferson (41031), Josephine (41033), Klamath (41035), Lake (41037), Malheur (41045), Sherman (41055), Tillamook (41057), Umatilla (41059), Union (41061), Wallowa (41063)*, Wasco (41065), Wheeler (41069)
UT Beaver (49001)*, Box Elder (49003), Cache (49005), Carbon (49007)*, Daggett (49009)*, Davis (49011)*, Duchesne (49013)*, Emery (49015), Garfield (49017), Juab (49023), Kane (49025), Millard (49027)*, Morgan (49029)*, Piute (49031), Rich (49033), Salt Lake (49035), Sanpete (49039)*, Sevier (49041), Summit (49043), Utah (49049), Wasatch (49051), Washington (49053)*, Wayne (49055)
WA Asotin (53003)+, Chelan (53007)+, Clallam (53009)+, Columbia (53013)+, Cowlitz (53015)+, Douglas (53017)+, Ferry (53019)+, Garfield (53023)+, Grays Harbor (53027)+, Island (53029)+, Jefferson (53031)+, King (53033)+, Kitsap (53035)+, Kittitas (53037)+, Klickitat (53039)+, Lewis (53041)+, Lincoln (53043)+, Mason (53045)+, Okanogan (53047)+, Pacific (53049)+, Pend Oreille (53051)+, Pierce (53053)+, San Juan (53055)+, Skagit (53057)+, Skamania (53059)+, Snohomish (53061)+, Spokane (53063)+, Stevens (53065)+, Thurston (53067)+, Whatcom (53073)+, Whitman (53075)+, Yakima (53077)+
WY Albany (56001), Carbon (56007), Converse (56009), Laramie (56021)*
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
09 St. Marys (09040001)+, Belly (09040002)+
10 Red Rock (10020001)+, Beaverhead (10020002)+, Ruby (10020003)+, Big Hole (10020004)+, Jefferson (10020005)+, Boulder (10020006)+, Madison (10020007)+, Gallatin (10020008)+, Upper Missouri (10030101)+, Upper Missouri-Dearborn (10030102)+, Smith (10030103)+, Sun (10030104)+, Two Medicine (10030201)+, Teton (10030205)+, Judith (10040103)+, Upper Musselshell (10040201)+, Shields (10070003)+, Upper North Platte (10180002)+, Medicine Bow (10180004)+, Little Medicine Bow (10180005)+, Middle North Platte-Casper (10180007)+, Glendo Reservoir (10180008)+*, Upper Laramie (10180010)+, Lower Laramie (10180011)+, Horse (10180012)+*, Cache La Poudre (10190007)+*, Lone Tree-Owl (10190008)+*, Crow (10190009)+*, Upper Lodgepole (10190015)+*
13 Conejos (13010005)+*, Rio Chama (13020102)+
14 Upper Green-Flaming Gorge Reservoir (14040106)+, Blacks Fork (14040107)+*, Great Divide closed basin (14040200)+*, Little Snake (14050003)+, Muddy (14050004)+*, Duchesne (14060003)+, Strawberry (14060004)+, Price (14060007)+, San Rafael (14060009)+, Upper Lake Powell (14070001)+, Muddy (14070002)+, Fremont (14070003)+
15 Upper Virgin (15010008)+*
16 Upper Bear (16010101)+, Bear Lake (16010201)+*, Middle Bear (16010202)+*, Little Bear-Logan (16010203)+, Lower Bear-Malad (16010204)+*, Upper Weber (16020101)+*, Lower Weber (16020102)+*, Utah Lake (16020201)+, Spanish Fork (16020202)+, Provo (16020203)+, Jordan (16020204)+, Hamlin-Snake Valleys (16020301)+*, Northern Great Salt Lake Desert (16020308)+, Curlew Valley (16020309)+*, Great Salt Lake (16020310)+*, East Fork Sevier (16030002)+, Middle Sevier (16030003)+, San Pitch (16030004)+*, Lower Sevier (16030005)+*, Beaver Bottoms-Upper Beaver (16030007)+*, Walker (16050303)+*, Walker Lake (16050304)+*
17 Upper Kootenai (17010101)+, Fisher (17010102)+, Yaak (17010103)+, Lower Kootenai (17010104)+, Moyie (17010105)+, Elk (17010106)+, Upper Clark Fork (17010201)+, Flint-Rock (17010202)+, Blackfoot (17010203)+, Middle Clark Fork (17010204)+, Bitterroot (17010205)+, North Fork Flathead (17010206)+, Middle Fork Flathead (17010207)+, Flathead Lake (17010208)+, South Fork Flathead (17010209)+, Stillwater (17010210)+, Swan (17010211)+, Lower Flathead (17010212)+, Lower Clark Fork (17010213)+, Pend Oreille Lake (17010214)+, Priest (17010215)+, Pend Oreille (17010216), Upper Coeur D'alene (17010301)+, South Fork Coeur D'alene (17010302)+, Coeur D'alene Lake (17010303)+, St. Joe (17010304)+, Upper Spokane (17010305)+, Lower Spokane (17010307), Franklin D. Roosevelt Lake (17020001), Kettle (17020002), Colville (17020003), Chief Joseph (17020005), Okanogan (17020006), Similkameen (17020007), Methow (17020008), Lake Chelan (17020009), Upper Columbia-Entiat (17020010), Wenatchee (17020011), Upper Yakima (17030001), Naches (17030002), Palisades (17040104)+, Salt (17040105)+, Upper Henrys (17040202)+, Willow (17040205)+, American Falls (17040206)+*, Blackfoot (17040207)+, Portneuf (17040208)+*, Lake Walcott (17040209)+*, Raft (17040210)+, Upper Snake-Rock (17040212)+, Beaver-Camas (17040214)+, Medicine Lodge (17040215)+, Big Lost (17040218)+, Big Wood (17040219)+, Camas (17040220)+, Little Wood (17040221)+*, C. J. Idaho (17050101)+, Bruneau (17050102)+*, Middle Snake-Succor (17050103)+, Upper Owyhee (17050104)+, Middle Owyhee (17050107)+, Jordan (17050108)+, Crooked-Rattlesnake (17050109)+, Lower Owyhee (17050110)+, North and Middle Forks Boise (17050111)+, Boise-Mores (17050112)+*, South Fork Boise (17050113)+*, Lower Boise (17050114)+*, Upper Malheur (17050116)+, Bully (17050118)+, South Fork Payette (17050120)+*, North Fork Payette (17050123)+, Weiser (17050124)+, Brownlee Reservoir (17050201)+, Burnt (17050202)+, Powder (17050203)+, Hells Canyon (17060101)+, Lower Snake-Asotin (17060103)+, Upper Grande Ronde (17060104)+, Lower Grande Ronde (17060106)+, Lower Snake-Tucannon (17060107), Palouse (17060108)+, Upper Salmon (17060201)+, Pahsimeroi (17060202)+, Middle Salmon-Panther (17060203)+, Lemhi (17060204)+, Upper Middle Fork Salmon (17060205)+, Lower Middle Fork Salmon (17060206)+, Middle Salmon-Chamberlain (17060207)+, South Fork Salmon (17060208)+, Lower Salmon (17060209)+, Little Salmon (17060210)+, Upper Selway (17060301)+, Lower Selway (17060302)+, Clearwater (17060306)+, Upper North Fork Clearwater (17060307)+, Lower North Fork Clearwater (17060308)+*, Middle Columbia-Lake Wallula (17070101), Walla Walla (17070102), Umatilla (17070103)+, Middle Columbia-Hood (17070105), Klickitat (17070106), Upper John Day (17070201)+, North Fork John Day (17070202)+, Lower John Day (17070204)+, Upper Deschutes (17070301)+, Little Deschutes (17070302)+, Beaver-South Fork (17070303)+, Upper Crooked (17070304)+, Lower Crooked (17070305)+, Lower Columbia-Sandy (17080001), Lewis (17080002), Lower Columbia-Clatskanie (17080003), Upper Cowlitz (17080004), Lower Cowlitz (17080005), Lower Columbia (17080006), Hoh-Quillayute (17100101), Queets-Quinault (17100102), Upper Chehalis (17100103), Lower Chehalis (17100104), Grays Harbor (17100105), Willapa Bay (17100106), Wilson-Trusk-Nestuccu (17100203)+, Upper Rogue (17100307)+, Middle Rogue (17100308)+*, Illinois (17100311)+, Chetco (17100312)+*, Fraser (17110001), Strait of Georgia (17110002), San Juan Islands (17110003), Nooksack (17110004), Upper Skagit (17110005), Sauk (17110006), Lower Skagit (17110007), Stillaguamish (17110008), Skykomish (17110009), Snoqualmie (17110010), Lake Washington (17110012), Puyallup (17110014), Nisqually (17110015), Deschutes (17110016), Skokomish (17110017), Hood Canal (17110018), Puget Sound (17110019), Dungeness-Elwha (17110020), Crescent-Hoko (17110021), Harney-Malheur Lakes (17120001)+, Silver (17120004)+, Summer Lake (17120005)+, Lake Abert (17120006)+
18 Sprague (18010202)+, Upper Klamath Lake (18010203)+, Lost (18010204)+, Upper Klamath (18010206)+, Goose Lake (18020001)+
19 Southeast Mainland (19010101)+, Ketchikan (19010102)+, Prince of Wales (19010103)+, Mainland (19010201)+, Kuiu-Kupreanof-Mitkof-Etolin-Zarembo-Wrangell Isla (19010202)+, Baranof-Chichagof Islands (19010203)+, Admiralty Island (19010204)+, Lynn Canal (19010301)+, Glacier Bay (19010302)+, Chilkat-Skagway Rivers (19010303)+, Taku River (19010304)+, Yakutat Bay (19010401)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A toad.
General Description: These warty toads are yellowish, dusky, tan, gray, or greenish on top, with dark markings ranging from a few spots to extensive mottling. Usually a light stripe extends along the middle of the back (most prominent in mature females; may be absent or inconspicuous in juveniles, which may have reddish warts). Parotoid glands (glandular swellings behind each eye) are oval. Cranial crests (hard ridges next to the eyes) are absent or indistinct. The tubercles on the underside of hind feet lack a sharp cutting edge; the foot tubercles are yellowish or orange in juveniles. Adult females are as large as 5 inches (12.7 cm) in snout-vent length, but males rarely exceed 3.7 inches (9.5 cm). Mature males have a dark patch on the inner surface of the thumb during the breeding season. Male lack vocal sacs but may produce repeated chirping sounds if grasped by hand (females usually are silent or emit few chirps). Larvae are black or dark brown on top; the tail fin may be heavily speckled with gray or black;and the eyes are about half way between the midline of the head and outside edge of the head. Larvae may reach a maximum total length about 2 inches (5 cm) but often are much smaller. Eggs are about 1.5-1.8 mm in diameter and are arranged in 1-3 rows (often two rows that appear to be a single zig-zag row) in long strings of two-layered jelly. Source: Hammerson (1999).
Reproduction Comments: The breeding period varies with local conditions; it may begin in January at low elevations but not until late spring or summer, as the winter snowpack begins to melt, in the high mountains. Females deposit an average of about 12,000 eggs/clutch, in two strands. Eggs hatch in a few days (warm temperatures) or in up to about 12 days (cold conditions). Larvae metamorphose in around 1-3 months, before the next winter; warm conditions result in the fastest larval development. Recently metamorphosed western toadlets sometimes form dense aggregations on the shores of breeding sites. Adult females may skip one or more years between successive breeding events. In northwestern Utah, single-year breeding populations at six sites ranged from a few dozen to nearly 250 individuals (Thompson 2004).

Ecology Comments: Ravens were significant predators on breeding toads in Oregon Cascades (Olson 1989). In Colorado, Corn (1993) observed a high rate of predation on breeding adults, evidently by ravens. Crow predation on adults was observed in Idaho (Brothers 1994.
Non-Migrant: N
Locally Migrant: Y
Long Distance Migrant: N
Mobility and Migration Comments: Migrates seasonally between aquatic breeding and terrestrial nonbreeding habitats.

In Colorado, Muths (2003) found that radio-tracked toads moved up to about 2 km from their breeding sites. Average maximum distance from the breeding site was 905 m in six females and 462 m in 8 males; mean distance of all locations was 721 m in females and 218 m in males; mean minimum distance was 392 m in females and 131 m in males. The longest distance was by a female that moved 2,324 m from her breeding site.

In Idaho, males moved an average of 581 m from the breeding pond and females moved an average of 1,105 m; the greatest total seasonal distances traveled by a male and a female toad were 0.94 km and 2.44 km, respectively (Bartelt et al. 2004). Some individuals remained in the breeding pond area, even after the pond dried.

In northwestern Utah, Thompson (2004) recorded movements of up to 5 km across upland habitat between two springs; the movement occurred between June of one year and January of the next year. Another toad moved 1.3 km between May of one year and May of the next year; the following June it was back at the original breeding location (Thompson 2004).

In Montana, individuals moved along stream corridors; based on recaptures (not radio-tagging), the longest documented movement was 1.5 km upstream in 6 days (Adams et al. 2005).

Riverine Habitat(s): CREEK, Low gradient, Pool, SPRING/SPRING BROOK
Lacustrine Habitat(s): Shallow water
Palustrine Habitat(s): HERBACEOUS WETLAND, Riparian, TEMPORARY POOL
Terrestrial Habitat(s): Cropland/hedgerow, Forest - Conifer, Forest - Hardwood, Forest - Mixed, Grassland/herbaceous, Sand/dune, Savanna, Shrubland/chaparral, Suburban/orchard, Woodland - Conifer, Woodland - Hardwood, Woodland - Mixed
Special Habitat Factors: Benthic, Burrowing in or using soil, Fallen log/debris
Habitat Comments: Western toads occur in a wide variety of habitats ranging from desert springs to mountain wetlands. They range into various upland habitats around ponds, lakes, reservoirs, and slow-moving rivers and streams; sometimes they move up to a few kilometers through uplands. For shelter, they dig their own burrow in loose soil or use those of small mammals or seclude themselves under logs or rocks. Egg laying sites include shallow areas of ponds, lakes, or reservoirs, or pools of slow-moving streams.
Adult Food Habits: Invertivore
Immature Food Habits: Herbivore
Food Comments: Metamorphosed individuals feed on various small terrestrial invertebrates. Larvae filter suspended plant material or feed on bottom detritus (Nussbaum et al. 1983).
Adult Phenology: Crepuscular, Diurnal, Hibernates/aestivates, Nocturnal
Immature Phenology: Crepuscular, Diurnal, Hibernates/aestivates, Nocturnal
Phenology Comments: Activity varies seasonally and geographically. At low elevations, western toads are active in daylight during cool weather of late winter and spring, but most activity is at night during warmer weather. They are active day or night in summer in the mountains, depending on conditions. They remain secluded in winter in cold climates.
Colonial Breeder: Y
Length: 13 centimeters
Economic Attributes Not yet assessed
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Management Summary
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Biological Research Needs: Further research on causes of declines is critical.
Population/Occurrence Delineation
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Group Name: Bufonid Toads

Use Class: Not applicable
Subtype(s): Breeding Site
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals (including larvae or eggs) in or near appropriate habitat where the species is presumed to be established and breeding.
Separation Barriers: Busy major highway such that toads rarely if ever cross successfully; roads with nonpermeable barriers to toad movement; urbanized areas dominated by buildings and pavement.
Separation Distance for Unsuitable Habitat: 1 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Opportunistic observations of various toad species in lowland habitats indicate regular movements of up to at least several hundred meters from the closest known breeding site (G. Hammerson, pers. obs.). Sweet (1993) recorded movements of up to 1 km in Bufo californicus. In defining critical habitat for B. californicus, USFWS (2000) included breeding streams and upland areas within a 25-m elevational range of each essential stream reach and no more than 1.5 km away from the stream. In northwestern Utah, Thompson (2004) recorded movements of Bufo boreas of up to 5 km across upland habitat between two springs during the summer-fall season. Another toad moved 1.3 km between May of one year and May of the next year; the following June it was back at the original breeding location (Thompson 2004). Most studies of toad movements have not employed radiotelemetry and were not designed to detect long-range movements or dispersal.

The separation distance for unsuitable habitat reflects the nominal minimum value of 1 km. The separation distance for suitable habitat reflects the good vagility of toads, their ability to utilize ephemeral or newly created breeding sites, and the consequent likely low probability that two occupied locations separated by less than several kilometers of suitable habitat would represent truly independent populations over the long term.

Inferred Minimum Extent of Habitat Use (when actual extent is unknown): .5 km
Date: 27Apr2005
Author: Hammerson, G.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 26Jan2010
NatureServe Conservation Status Factors Author: Reichel, J. D., and G. Hammerson
Element Ecology & Life History Edition Date: 26Jan2010
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

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