Ecology and Vulnerability

Eastern Spadefoot Toad

Background
Eastern spadefoot toads are short-legged toads with large heads and cat-like vertically elongated pupils ⁶. They are named after their spade-like protrusion, or tubercle, on their hind feet ². Spadefoot toads belong to a primitive amphibian family that are neither true frogs or true toads ⁶. They range from southern Florida north and westward to Missouri and northward to Massachusetts ¹³. Although isolated inland populations exist, spadefoot toads in Massachusetts are primarily restricted to Cape Cod. They can be found along river floodplains and other low lying areas with leaf litter ⁶. Spadefoot toads can burrow up to eight feet below the ground’s surface, preferably in sandy loam soil, to hibernate in the winter and to avoid desiccation (drying out) in the summer.

They require fish-free isolated ponds for breeding, but otherwise live in surrounding uplands ⁵. Breeding occurs anytime between March and August and is typically confined to a short window of time of just several days within a given year that occurs during or just after heavy rainfall events ¹³. Larval toads, or tadpoles, feed on plankton, while adults eat most insects ⁶.  Spadefoot toads are difficult to observe in the wild because of their rarity, small home ranges (estimated at ~110 square feet), nocturnal behavior, and ephemeral breeding habitats. ^6,8.

Spadefoot toads are listed as threatened under the Massachusetts Endangered Species Act 7. They are threatened by human development, roads, and agricultural pesticides. Deforestation and changes in forest fire regimes have also impacted spadefoot toad populations by changing forest floor soil and vegetation types, as well as light penetration, soil distribution, leaf litter, and moisture levels ^4,9,11.

Climate Impacts
Spadefoot toads are vulnerable to many aspects of climate change. Because spadefoots depend on specific soil and seasonal hydrologic conditions, particularly along the coast, they are at risk to sea level rise, changes in hydrology, and increased erosion from terrestrial runoff.  Early life stages are sensitive to high salinity, thus sea level rise specifically threatens coastal populations ¹. Spadefoots are extremely reliant on spring and summer storm events for breeding, which may be disrupted by projected changes in the timing, frequency, and magnitude of precipitation events. Projected increases in coastal storm surge could alter the composition and distribution of preferred sediments, potentially impacting burrowing, over- winter and summer survival.

Droughts are projected to become more frequent in the Northeast, which threatens the initiation and timing of breeding and the survival of offspring. Spadefoot tadpoles have shown the ability to speed up development when water levels decrease; therefore they may have some adaptive capacity to adjust to changing temperatures ¹⁰ and withstand some future extreme events ¹². Finally, since sex determination is temperature dependent in spadefoots and other amphibians ³, increasing temperatures may impact toad populations in terms of the ratio of males to females in local and regional populations.