© 2007 Twan Leenders (1 of 11)
Bufo quercicus Holbrook, 1840
1. Historical versus Current Distribution. Oak toads (Bufo quercicus) range from the Coastal Plain of southeast Virginia, west to Louisiana. They are found throughout Florida and on some of the lower Florida Keys (Conant, 1975; Dalrymple, 1990; Dodd, 1994; Behler and King, 1998). Their current range has been extended since the early description by Holbrook (1842; see Duellman and Schwartz, 1958; Ashton and Ashton, 1988).
2. Historical versus Current Abundance. Oak toads are abundant in southern pine wood habitats. Wright (1932; Wright and Wright, 1949) reported as early as 1921 that they were locally abundant in the Okefenokee Swamp (Georgia). Their local abundance was also reported in several locations in Florida (in 1895) and Louisiana (in 1923; Wright and Wright, 1949; Hamilton, 1955). In subtropical Florida, these toads are most common in low elevation pinelands (Dodd, 1994). They remain abundant in undisturbed preferred habitats throughout their range. However, due to rapid human development throughout much of the south and concomitant habitat destruction, as well as the introduction of exotic species via the pet trade (Meshaka, 2003), their numbers can be expected to steadily decrease (Wilson and Porras, 1983).
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Mating occurs from April–October, with peak activity in the early spring (Harper, 1931; Einem and Ober, 1956). Heavy, warm spring rains stimulate mating behavior (Wright and Wright, 1949). Males typically call from flooded fields, the edges of ponds and puddles, and from clumps of understory vegetation (Dalrymple, 1990). Oak toads are distinctive in that they are primarily active during the day (Dalrymple, 1990), although both daytime and nighttime breeding has been observed (Punzo, 1992a). Most adults are collected during the summer throughout their range, whereas juveniles are most active during late summer and early autumn (Dodd, 1994).
ii. Breeding habitat. Oak toads prefer shallow pools, cypress and flatwood ponds, and ditches. Eggs are usually attached to grass blades 4–12 cm beneath the surface of the water (Hamilton, 1955; Ashton and Ashton, 1988). Following breeding, adults exhibit a y-axis orientation to exit ponds, suggesting animals use celestial cues to navigate (Goodyear, 1971).
i. Egg deposition sites. The eggs are laid in strings or bars that are typically attached to vegetation; each string contains 3–8 eggs (Wright, 1932).
ii. Clutch size. Females typically lay 300–500 eggs, each approximately 1 mm in diameter (Hamilton, 1955; Dodd, 1994). Embryos usually hatch from 24–36 hr after fertilization.
C. Larvae/Metamorphosis. Oak toad tadpoles reach a maximum length of 18–19.4 mm at stage 41 in 4–5 wk, and toadlets range from 7.2–8.9 mm SVL (Volpe and Dobie, 1959). Tadpoles are non-selective filter feeders and ingest a diverse array of algae as well as decaying animal material (Dalrymple, 1990).
D. Juvenile Habitat. Same as adult habitat.
E. Adult Habitat. Oak toads are most often associated with open canopied oak and pine forests containing shallow temporary ponds and ditches (Duellman and Schwartz, 1958; Dodd, 1994) and wet prairies, characterized by short hydroperiods, of the southeastern coastal plain (Hamilton, 1955; Pechmann et al., 1989). Oak toads prefer areas without permanent water and well- to poorly drained soils. They commonly seek refuge under boards and logs or in shallow depressions or burrows surrounded by vegetation, including cabbage palms (Sabal palmetto) and saw palmettos (Serenoa repens; Hamilton, 1955; Duellman and Schwartz, 1958). The minimum habitat area has not been delineated for oak toads (Dalrymple, 1990), however, an earlier study by Hamilton (1954) suggested that an area as small as 1 ac could sustain a breeding population.
F. Home Range Size. Unknown.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. During the winter in the northern part of their range, oak toads remain underground in burrows and shallow depressions for intermittent intervals depending on ambient temperature conditions (Harper, 1931; Wright and Wright, 1949). During cold weather they have also been found in rotten oak logs and under pine bark (Hamilton, 1955).
I. Seasonal Migrations. During heavy rains, adults will move up to 80 m from refuge sites to breeding ponds (Wright, 1932; Dodd, 1994).
J. Torpor (Hibernation). May hibernate from early December to early March (Harper, 1931).
K. Interspecific Associations/Exclusions. Unknown.
L. Age/Size at Reproductive Maturity. Oak toads are the smallest toads in North America, with an adult body size ranging from 20–26 mm SVL for breeding males and 24–30 mm for females (Hamilton, 1955). Age at first reproduction is 1.5–2.3 yr (Ashton and Ashton, 1988; Dalrymple, 1989).
M. Longevity. Oak toads are known to live 4 yr (Wright, 1932; Ashton and Ashton, 1988).
N. Feeding Behavior. Adults are insectivorous with a strong preference for ants (Punzo, 1995). Adults also feed on beetles, lepidopterans, aphids, dipterans, orthopterans, spiders, pseudoscorpions, centipedes, and mollusks (Duellman and Schwartz, 1958; Punzo, 1995). Juvenile diets include a high percentage of collembolans, ants, small spiders, and mites (Crosby and Bishop, 1925; Punzo, 1995).
O. Predators. A number of animals have been observed attacking (and in some cases killing and ingesting) oak toads, including raccoons, crows, hog-nosed snakes (Heterodon sp.), garter snakes (Thamnophis sp.), gopher frogs (Rana capito), and marine toads (Bufo marinus; Harper, 1931; Wright, 1932; Hamilton, 1954).
P. Anti-Predator Mechanisms. As with many other bufonids, oak toads will inflate their bodies (unken reflex) when confronted by potential snake predators (Duellman and Trueb, 1986; Heinen, 1995). They also are capable of secreting toxins from the parotoid glands (Licht, 1967c). Their eggs appear to possess some toxic properties (Licht, 1968).
Q. Diseases. Unknown.
R. Parasites. Nematodes of the genera Oxysomatium and Oswaldocruzia are reported to parasitize oak toads (Hamilton, 1955).
4. Conservation. In Florida, progressive development, drainage of wetlands, and urbanization always pose a potential threat to amphibian populations. Such anthropogenic activities have substantially reduced natural areas where oak toads breed, including wet prairies, freshwater marshes, margins surrounding cypress swamps, hardwood swamps, and upland areas. Sensitive wetland habitats tend to be small and localized and are therefore more readily threatened by habitat destruction and fragmentation. Sedimentation and runoff of silt during highway and home construction projects, as well as pollution from agricultural pesticides and heavy metals, pose a serious threat to the quality of aquatic breeding sites and survival of tadpoles (Punzo, 1997). State and federal agencies should carefully monitor oak toad populations throughout the state and implement specific habitat management programs to ensure the long-term survival of this species. Further studies should focus on a more detailed analysis of post-breeding movements and home ranges of juveniles and adults.
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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