Southern toad (Bufo terrestris)
After leaving the Big Cypress National Preserve, the East Aiken students hiked to the National Audubon Society’s Corkscrew Swamp Sanctuary near Naples, Florida. The Corkscrew Sanctuary is a well-known rookery for wood storks, which have nested there for more than 80 years. In the 1950’s and ’60’s, the largest wood stork nesting colonies were in southern Florida, and the numbers of wood storks in the Corkscrew/Big Cypress sub-population were the greatest of all colonies. In the 1960’s the colony of wood storks at Corkscrew often totaled more than 5,000 breeding pairs; in more recent years the number of pairs is usually far fewer. From 1967 to 1982 the wood stork population decreased by 75% in southern Florida, probably due to the altered hydrology of wetlands and their ability to support wood storks. Although fewer birds have nested in southern Florida in recent years, the numbers nesting in northern Florida, Georgia, and South Carolina have been increasing. For more information on wood storks, see US Fish and Wildlife Service Red Book and Wood Storks in Everglades National Park.
By January 10, 2000 the school reached the Fort Myers area, where they were able to visit the J.N. "Ding" Darling National Wildlife Refuge, as well as other refuges in the area (Caloosahatchee NWR, Island Bay NWR, Natlacha Pass NWR, Pine Island NWR—visit the Ding Darling web site).
As is the recurring theme in South Florida, the health of the J. N. "Ding" Darling NWR and nearby refuges depends on the water it receives. The quality, quantity, and timing of water from the Caloosahatchee River (originating in the Kissimmee River and Lake Okeechobee) have been altered, and some wildlife has been adversely affected. Three species of toads in the area (the oak toad, the southern toad, and the narrow-mouthed toad) seem to be doing fine, though.
Southern Toad (Bufo terrestris)
It is hard to imagine not having the musical calls of toads to enrich our lives. The trill of the male southern toad can be heard from quite a distance away. He seems to say, "I’m here…over here. It’s a beautiful night. Oohhhh wait…did something move over there? Come for a visit." Ah, the trill of victory (hey—gimme a break—if it were a marked toad I could have also said the agony of the feet).
But, as PARC (Partners in Amphibian and Reptile Conservation) members are trying to point out, the alluring choruses of frogs and toads are not something we can take for granted. There is evidence of amphibian and reptile population declines, and sometimes species extinctions, on all continents where they occur. The major threats identified by PARC are: habitat loss, unsustainable use, environmental contaminants, disease and parasitism, introduced species, and global climate change. Some species of toads are impacted by all these threats, perhaps with the exception of unsustainable use (after all, many states have banned toad licking). For more about threats to reptile and amphibian populations, visit the PARC "threats to herps" page.
In the case of frogs and toads in the southeastern U.S., two of the threats listed above top the list: habitat loss and environmental contaminants. We'll have more on habitat loss in the future, but what about environmental contaminants?
Researchers at the Savannah River Ecology Lab (SREL) have pointed out that approximately 120,000,000 tons of coal fly ash, a by-product of coal burning, are produced each year just in the U.S. Coal ash waste contains metals such as arsenic, copper, and selenium, which may be toxic at high concentrations. Often the coal ash waste is associated with wetlands, and therefore can be a threat to aquatic organisms.
Coal ash may cause developmental, physiological, and behavioral abnormalities in amphibians. SREL scientists studied southern toads to determine the concentrations of the coal-ash trace elements in their bodies. The researchers compared concentrations of 20 trace elements in adult southern toads inhabiting coal ash settling basins with toads that were not exposed to the coal wastes. High levels of arsenic, selenium, and vanadium occurred in toads captured at the coal-ash contaminated wetlands. The coal-ash toads also had stress hormone levels six times higher than the uncontaminated toads. Even toads that were only exposed to the contamination for a short time (7 weeks) accumulated high levels of metals. The researchers concluded that adult toads can bioaccumulate particularly high levels of selenium and may be useful bioindicators in agricultural and coal ash-impacted habitats.
For more on the effects of coal ash, see Justin Congdon's physiological ecology web site.