The Eastern Spadefoot Toad gets its name from distinctive protruding cartilage “spades” on its hind feet. This feature helps the animal to dig itself quickly below ground where it spends much of its life, emerging on warm stormy nights to feed and breed in temporary water bodies.
Historically widespread in Massachusetts, the spadefoot is now found in only a handful of locations in the state due to development. It’s classified as threatened on the state’s endangered species list. The two remaining population strongholds occur on Cape Cod, including Sandy Neck Barrier Beach in Barnstable and the Provincelands in the Cape Cod National Seashore.
More than ten years ago, we wondered—could a spadefoot toad population on the Cape be restored and, if so, where?
In 2011, Long Pasture Sanctuary director Ian Ives and Bryan Windmiller of Zoo New England set out to re-establish the species at Mass Audubon’s Ashumet Holly Wildlife Sanctuary in East Falmouth. Back in the 1970’s and ‘80’s, spadefoots were documented to have existed at Ashumet. By the early 2000’s, they were all but gone.
It was determined that restoring spadefoots at Ashumet would require “seeding” individuals from the healthy Sandy Neck population. This would involve collecting eggs and tadpoles, headstarting them (by partnering with Cape Cod schools) and translocating the young toads—or toadlets– to breeding pools created specifically for spadefoots.
Like wood frogs, spadefoots depend on temporary pools of water free of fish and other predators to successfully breed. At Ashumet, we created or restored seven vernal pools of varying sizes and depths. Over the years, we have raised and released 40,000 spadefoots. (We’ve learned that school children are very good at captive-rearing toads!)
But the real work is determining the toads’ survival rate and what they require to successfully reproduce and maintain a viable population.
Most spadefoot tadpoles never make it out of their pools due to water drying before they metamorphose (develop into young toads). We remove that limitation from the equation by translocating newly metamorphosed toads to Ashumet. Over hundreds of search hours in the last 9 years, we have confirmed that at least 123 translocated toads have survived at Ashumet. And through marking and recapturing, we’ve learned that some toads have survived for at least 4 years.
Our search for a better way to find our translocated spadefoots has led to an intriguing partnership with Dr. Kristine Hoffman at St. Lawrence University, who’s been working with Newt, a toad-sniffing detector dog! Newt, a Labrador retriever, has the potential to increase overall capture effort and provide us with greater detail on our population. Newt continues to progress in his training having successfully located toads in the wild this season.
We also need to find evidence of breeding. Unlike spring peepers, which begin to call for mates after the first warm rainy night in March and continue through spring, spadefoots have more specific requirements. They need heavy rains and high water tables to sustain any temporary pools long enough for their eggs and tadpoles to develop. Due to reduced spring rainfall on the Cape, spadefoots at Ashumet have not had these conditions present in the last 2 years, which may have discouraged any potential breeding attempts. Another challenge the toads face in the Northeast—the northern end of their range—is relatively cool spring weather. Cool temperatures retard the development rate of spadefoot tadpoles, confounding their ability to get out of their pools in time. Adaptations that were effective in warm climates are seemingly less successful in cooler regions, effectively explaining their rarity in Massachusetts, and complicating our efforts to restore their populations.
Despite regular visual and dip net surveys and even audio recordings “listening” for calling male toads, we’ve found no evidence of breeding so far at Ashumet Holly. Why? In addition to the adaptive challenges we’ve mentioned, there are many other variables at play. For instance: many amphibians return to the pools where they started their lives. Does this apply to spadefoots and are translocated animals at a disadvantage? Our work has led to another question–are male spadefoot breeding calls innate or learned? Could our captive-raised animals be missing out on an important lesson?
We are slowly testing individual hypotheses to rule out potential causes and get closer to the answers, so stay tuned for updates from the 2021 field season!
This post was contributed by Jay Cordeiro, Spadefoot Toad Project Coordinator and Ian Ives, director, Mass Audubon’s Long Pasture Wildlife Sanctuary. Ian recently spoke about the spadefoot project at the annual meeting of the Rhode Island Natural History Survey.