Bufo woodhousii Girard, 1854
Brian K. Sullivan1
1. Historical versus Current Distribution. The type locality of Woodhouse's toads (Bufo woodhousii) is from San Francisco Peaks, New Mexico (= Arizona; Girard, 1854). Woodhouse's toads occur from south‑central Washington, far eastern Oregon and California, Nevada, south‑central Idaho, southern and eastern Montana, and southern North Dakota, south through Utah, Colorado, South Dakota, Nebraska, Kansas, Oklahoma, Texas, New Mexico, and Arizona to Mexico. They range from near sea level (Salton Sea, California) to almost 2,500 m (Stebbins, 1951; personal observations). Additional comments on distribution can be found in Tanner (1931), Bragg (1940b), Smith (1950), Lowe (1964), Collins (1982), Hammerson (1982a), Dixon (1987), Conant and Collins (1991), and Degenhardt et al. (1996).
Although in the past some have considered Woodhouse's toads and Fowler's toads (B. fowleri) to be conspecific (e.g., Conant and Collins, 1991), Sullivan et al. (1996a) summarized evidence (behavior, morphology, genetics) supporting the recognition of these taxa as separate, full species. One western subspecies is recognized (B. w. australis; Shannon and Lowe, 1955); the status of a second subspecies (B. w. velatus), reported to occupy the zone of intergradation between Woodhouse's and Fowler's toads, is uncertain (Conant and Collins, 1991; Sullivan et al., 1996a).
2. Historical versus Current Abundance. Historical abundance is unknown; localized populations can be abundant, even in urbanized and other disturbed habitats (e.g., Hammerson, 1982a). David Bradford and colleagues (personal communication) surveyed sites in southern Nevada and found Woodhouse's toads at all (n = 4) historical collecting localities they examined. They noted that Woodhouse's toads are now present at sites near Las Vegas that were not occupied historically. Similarly, Sullivan (1986b, 1993) noted the apparent range expansion of Woodhouse's toads and coincident decline of Arizona toads (B. microscaphus) at degraded riparian sites in Arizona. Hammerson (1982a) noted that Woodhouse's toads appear to have expanded their range in agricultural areas formerly occupied by red-spotted toads (B. punctatus) in Colorado. Woodhouse's toads also appear to be expanding their range in southeastern California in the vicinity of Palm Springs.
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Across their range, breeding occurs from February–September (Stebbins, 1951; personal observations). In the Sonoran Desert, populations along larger streams and rivers breed on warm (air temperature > 15 ˚C), rainless nights in the spring (February–June), whereas populations occurring in open desert flats breed immediately after summer rainstorms (June–September). In the Great Plains, populations typically breed in ponds, lakes, and rain‑formed pools from February–July. Breeding periods span 2–4 mo for riparian-breeding populations and 1–5 nights for pool-breeding populations. For example, in central Arizona, chorus activity occurred on a total of 25–56 nights over the course of three spring seasons, whereas in central Texas, chorus activity occurred on only a total of 15–17 nights through spring and summer in each of two seasons (Sullivan, 1989b).
Males have been observed calling in shallow water, completely exposed on shore at the water's edge, and on land near water (Stebbins, 1951; personal observation). The advertisement call is a nasal "waaah," from 1–4 s in duration, 1.4–2.0 kHz in frequency, and rapidly pulsed (80–200 p/s; see Stebbins, 1951; Sullivan et al., 1996a).
Long-distance migrations of large numbers of individuals have not been reported. Adults in populations from relatively arid regions may reside throughout the year in the vicinity of streams used for breeding.
ii. Breeding habitat. Standing water is apparently preferred for breeding—either pools in river channels following spring run‑off, artificial ponds and reservoirs, or rain‑formed pools and cattle tanks in open desert flats (Stebbins, 1951; Sullivan, 1982b; personal observation). A great variety of breeding habitats are used (Bragg, 1940b; Stebbins, 1951; Hammerson, 1982a; Sullivan, 1982b, 1989b).
i. Egg deposition sites. Descriptions of eggs and larvae can be found in Stebbins (1951, 1985). Altig et al. (1998) provide a key to larvae of Woodhouse's toads and their relatives. Eggs are laid in long gelatinous strands and are small, 3–4 mm in diameter.
ii. Clutch size. Krupa (1995) provided data on maximal clutch size (> 28,000 eggs) for midwestern Woodhouse's toads.
C. Larvae/Metamorphosis. Larvae are generally black, although the venter of the tail is pale. Larvae are often observed in large aggregations in stream and pond habitats, typically in standing water, resting on muddy substrate. In central Arizona, the length of the larval period was 8 wk for pond breeding populations (31 March–1 June; personal observations), whereas development lasted 5–7 wk in Oklahoma (Bragg, 1940b). Woodward (1987) found that larvae grew more slowly when housed with larger conspecific larvae. Metamorphosis begins at a tadpole length of about 30 mm total length (Bragg, 1940b; personal observation). Recently metamorphosed toadlets average 12–15 mm SVL (Bragg, 1940b; personal observation). Details on larval development can be found in Bragg (1940b). Verma and Pierce (1994) described acid tolerance of larvae. Cupp (1980) analyzed thermal preferences of larvae.
D. Juvenile Habitat. Juveniles may be largely restricted to relatively mesic environments associated with breeding habitats of adults. Recently metamorphosed young have been observed near breeding pools in Arizona in April and May (Stebbins, 1951; personal observation). Bragg (1940b) documented rapid growth of almost 10 mm/mo in recently metamorphosed toadlets. Labanick (1976a) and Clarke (1977) described post-metamorphic growth in the closely related Fowler's toad.
E. Adult Habitat. Adults are found in a variety of habitats (Stebbins, 1951). In the western states, Woodhouse's toads are often associated with larger riparian corridors at lower elevations, and moist meadows, ponds, lakes, and reservoirs at higher elevations. They can be common in disturbed habitats such as canals and irrigated fields, golf courses, and urban parks with ponds. O'Connor and Tracy (1992) described thermoregulation and thermal preferences in juveniles, and Swanson et al. (1996) described freeze‑tolerance of adult Woodhouse's toads. Additional comments on habitat use can be found in Bragg (1940b).
F. Home Range Size. Unknown.
G. Territories. Unknown. Males defend a calling territory at breeding sites (Sullivan, 1982b).
H. Aestivation/Avoiding Dessication. Populations breeding along streams may aestivate during the dry summer.
I. Seasonal Migrations. Unknown.
J. Torpor (Hibernation). Unknown, although populations are presumed to hibernate during cooler and/or dryer months (about October–February) over most of the range.
K. Interspecific Associations/Exclusions. Hybridization has been documented between Woodhouse's toads and both Sonoran Desert toads (B. alvarius) and Great Plains toads (B. cognatus) in Arizona (Gergus et al., 1999), American toads (B. americanus) in the Midwest (Malmos, 1992), Fowler's toads in the Midwest (Meacham, 1962; Sullivan et al., 1996a), Houston toads (B. houstonensis) in Texas (Hillis et al., 1984), Arizona toads in Arizona and Utah (Sullivan and Lamb, 1988; Sullivan, 1995), red-spotted toads in northern Arizona and southern Colorado (Malmos et al., 1995), and Gulf Coast toads (B. valliceps) in Texas (Thornton, 1955). Hybrids are generally easily identified by their morphology (intermediate to parentals) and aberrant calls.
In southern Arizona, Woodhouse's toads have been observed breeding with Sonoran Desert toads, Great Plains toads, green toads (B. debilis), Arizona toads (B. microscaphus), red-spotted toads, canyon treefrogs (H. arenicolor), Couch's spadefoot toads (Scaphiopus couchii), American bullfrogs (Rand catesbeiana), and lowland leopard frogs (R. yavapaiensis). In central Texas, Woodhouse's toads breed sympatrically with cricket frogs (Acris crepitans), green toads, Gulf Coast toads, western narrow-mouthed toads (Gastrophryne olivacea), spotted chorus frogs (Pseudacris clarkii), Strecker's chorus frogs (P. streckeri), and Rio Grande leopard frogs (Rana berlandieri).
L. Age/Size at Reproductive Maturity. In central Arizona, calling males at breeding aggregations (n = 61 males sampled) ranged in size from 69–98 mm SVL (Sullivan, 1982b). Reproductive females (n = 38) in this same population ranged from 84–109 mm SVL (Sullivan, 1982b). In central Texas, calling males at breeding aggregations (n = 98 males sampled) ranged in size from 73–104 mm SVL (Sullivan, 1989b). Reproductive females (n = 22) in this same population ranged from 79–110 mm SVL (Sullivan, 1989b).
M. Longevity. Given observations on close relatives (e.g., Fowler's toads and Arizona toads), it is presumed that males typically reach reproductive maturity within 1 yr of metamorphosis, females within 2 yr.
N. Feeding Behavior. Presumably feed on a variety of invertebrates; descriptions of their diet can be found in Bragg (1940b) and Stebbins (1951). Flowers and Graves (1995) described the diet of juvenile toads immediately following metamorphosis and reviewed previous reports on diet in Woodhouse's toads. Benally et al. (1996) discussed the feeding mechanics of adults.
O. Predators. Bragg (1940b) listed predators of adults, including bull snakes (Pituophis melanoleucus), rat snakes (Elaphe sp.), American bullfrogs, and a hawk. Woodward and Mitchell (1990) documented evidence of predation on male (15 of 120) Woodhouse's toads in a breeding aggregation in New Mexico and suggested that a mammalian predator, possibly a skunk, was responsible. I observed similar disemboweled carcasses in central Texas at a breeding aggregation in 1987, and I agree with Woodward and Mitchell (1990) that a small mammalian predator was likely responsible. Parmley (1982) documented predation on Woodhouse's toads by a roadrunner in Texas. Morin (1995) documented predation (in artificial enclosures) by eastern newts (Notophthalmus viridescens) and marbled salamanders (Ambystoma opacum) on larvae of the closely related Fowler's toads. Similarly, Lawler (1989) documented larval behavior in response to the presence of potential predators, eastern newts and banded sunfish (Enneacanthus obesus), in Fowler's toads. Kruse and Stone (1984) noted that largemouth bass (Micropterus salmoides) find Woodhouse's toad larvae distasteful and learn to avoid them as prey.
P. Anti‑Predatory Mechanisms. Skin secretions presumably afford some protection against some predators for larvae (Kruse and Stone, 1984) and adults (Cei et al., 1968).
Q. Diseases. Shiveley et al. (1981) reported on bacterial infections.
R. Parasites. Goldberg et al. (1996c) reported on the helminth fauna (cestodes, nematodes) for populations sympatric with Arizona toads in southern Arizona; Hardin and Janovy (1988) described cestode infestations. McAllister et al. (1989) presented a comparative analysis of endoparasites in a community of three bufonids in Texas.
4. Conservation. Widespread declines have not been noted for Woodhouse's toads, although they are listed as a Protected species by the State of Oregon (Levell, 1997). While Hovingh (1997) indicated that Woodhouse's toads might be absent from southeastern Idaho and adjacent, historically occupied, parts of northern Utah, Mulcahy et al. (2002) confirmed the presence of Woodhouse's toads in both regions. Similarly, D. Bradford and colleagues (personal communication) documented the continued presence of Woodhouse's toads at historical localities in southern Nevada. The expansion of Woodhouse's toads into areas formerly occupied by Arizona toads in central Arizona (Sullivan, 1986, 1993) stands in contrast to the declines noted for other anurans in the past decade. However, some local declines are suspected and require continued monitoring: Woodhouse's toads appear absent from the Santa Cruz River floodplain in the vicinity of Tucson, Arizona (P. Rosen, personal communication), and from the vicinity of Austin, Texas (D. Hillis, personal communication).
Acknowledgments. Rob Bowker, Mike Demlong, Erik Gergus, Tom Jones, Keith Malmos, Kit Murphy, Dave Pfennig, Elizabeth Sullivan and Bill Wagner assisted with some observations. Fieldwork was supported in part by the Heritage Fund, Arizona Game and Fish Department.
1Brian K. Sullivan
Department of Life Sciences
Arizona State University West
P.O. Box 37100
Phoenix, Arizona 85069
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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