The Detroit Zoo has sent 6,855 Puerto Rican crested toad tadpoles to Puerto Rico for release into the wild, the Detroit Zoological Society announced this week. The tadpoles, hatched and raised at the zoo's National Amphibian Conservation Center in Royal Oak, Michigan, were shipped to Río Encantado — a rainforest area in the northern municipality of Manatí — where they will be released into temporary freshwater pools and, if they survive to maturity, add to the island's critically diminished wild population. The shipment brings the total number of tadpoles the Detroit Zoo has raised and released as part of the program to 143,195.
"Each of these tadpoles represents a lot of care, coordination and hope," said Mark Vassallo, curator of amphibians for the Detroit Zoological Society. "For our team, it's incredibly meaningful to know that work happening here at the Detroit Zoo can help support the future of a species in Puerto Rico. Amphibians are facing serious challenges globally, and efforts like this show how zoos and the communities that support them can play an important role in protecting vulnerable wildlife."
The World's Longest-Running Amphibian Reintroduction Program
The Detroit Zoological Society has been participating in the cooperative breeding and reintroduction program for the Puerto Rican crested toad since 1995 — making it part of what is described as the longest-running amphibian reintroduction program in the world. The program is a collaborative effort involving accredited zoos across North America working alongside Puerto Rican wildlife authorities to counter a population collapse that has reduced the species to a fraction of its historic range. Tadpoles from the program are released at sites in the north of Puerto Rico, including Río Encantado, rather than at the species' historically documented southern range near Guánica, because the northern release sites offer more stable habitat conditions.
The Puerto Rican crested toad is a critically endangered amphibian found nowhere else on earth. According to the Puerto Rican Crested Toad Conservancy, population counts of toads collected during breeding events over the past three decades have fluctuated widely — ranging from as few as 300 to approximately 3,000 individuals observed in Guánica National Forest, a protected coastal dry forest in southwestern Puerto Rico. That area is itself vulnerable to environmental catastrophes including hurricanes and prolonged drought, conditions that have become more frequent and severe in the decades since the toad was first listed as threatened.
Why the Puerto Rican Crested Toad Needs Help
The species' decline has been driven by a combination of factors that have compounded over more than a century. Chief among them is habitat alteration — the conversion of the lowland forests, ponds, and seasonal wetlands the toad depends on for breeding into agricultural land and urban development. The species requires healthy temporary freshwater pools to breed successfully, and those microhabitats have been drained, paved over, or degraded across much of Puerto Rico. The problem was severely worsened in the twentieth century when sugar cane growers introduced the marine toad — also known as the cane toad or bufo toad — to the island in an attempt to control agricultural pests. The introduced toad proved enormously destructive, outcompeting and preying on native amphibians and consuming the crested toad's eggs and young.
Additional invasive species continue to threaten the toad today, including Cuban tree frogs, which compete aggressively for food and space. Predators including feral dogs, feral cats, and mongoose — the latter introduced in the nineteenth century to control snakes in sugar cane fields — further reduce the toad's survival odds in the wild. Puerto Rican crested toads reach sexual maturity at approximately eighteen months of age, meaning tadpoles released this season, if they survive, could begin contributing to wild breeding populations as early as late 2027.
What Makes the Crested Toad Distinctive
The Puerto Rican crested toad has a striking appearance that sets it apart from other Caribbean amphibians. Adults grow between three and four inches in length and are covered in greenish-brown pebbled skin with marbled golden eyes that give them an almost prehistoric look. The toad takes its common name from a pronounced bony ridge — or crest — that runs above and behind its eyes and gives its profile a blunt, upturned profile. The species also has the unusual ability to nearly flatten its body completely, allowing it to squeeze into narrow crevices in limestone rock formations where it shelters during the dry season. The hooked, upturned nose is another identifying characteristic that zookeepers note makes them recognisable even when the animal is mostly hidden.
The Detroit Zoo maintains a breeding population of Puerto Rican crested toads at its National Amphibian Conservation Center, where the animals are managed as part of the AZA Species Survival Plan — a cooperative program among accredited zoos designed to maintain genetically diverse and demographically healthy populations of threatened species in human care. The zoo's work on this species is one component of a broader institutional commitment to amphibian conservation at a moment when the global amphibian extinction crisis — driven by habitat loss, disease, climate change, and invasive species — has made frogs and toads the most threatened vertebrate group on earth.
