Brookfield Zoo Helping Puerto Rican Crested Toads Recover

The island of Puerto Rico’s most famous resident amphibians is a group of frogs called Coquí, tiny frogs that vociferously call their name into the tropical nights. The rich fauna of the island includes only one native species of toad, the Puerto Rican Crested Toad (Peltophryne lemur).

Unfortunately, this toad faces several threats in the wild and is listed as critically endangered by the IUCN. A group of 19 zoos and aquariums, including Brookfield Zoo, are working alongside the Puerto Rican Department of Natural and Environmental Resources (PRDNER) and the United States Fish and Wildlife Service (USFWS) to ensure this species isn’t lost to extinction by reintroducing tadpoles back to the toad’s historic range.


Why Are Puerto Rican Crested Toad Endangered?
These toads originally lived in dry rocky habitats in several locations throughout Puerto Rico and the Virgin Islands. Over time, loss of breeding sites to development and the introduction of invasive species including the marine toad (Bufo marinus) has led to the loss of natural populations throughout much of the Puerto Rican Crested Toad’s original range. The species is no longer believed to survive in the Virgin Islands, and on Puerto Rico, they are mostly confined to only a couple of populations in the dry-forests in and around Guánica Commonwealth Forest. Over the past 35 years, the original natural population has fluctuated between 300 and 3,000 individuals. 

In 1984, concerned with the downward population trend, the Association of Zoos and Aquariums (AZA) named the Puerto Rican Crested Toad the first amphibian to have a Species Survival Plan (SSP). This SSP designation set into motion an ambitious plan to reintroduce zoo and aquarium bred toads into their former range. Like all of the nearly 500 AZA SSPs, the Puerto Rican crested toad SSP is managed by a coordinator who looks at the collective population of animals cared for at zoos and aquariums and recommends animal pairings to maximize the genetic diversity. For the Puerto Rican crested toads, most of the tadpoles produced from these pairings are sent back to Puerto Rico to be released in man-made pools at six sites in the former range of the toads.


How Does The Process Work?
The process of producing tadpoles to be released in the wild is one of many conservation initiatives taking place at Brookfield Zoo. Brookfield Zoo currently maintains a colony of 26 toads in a behind-the-scenes room at the Living Coast. The animals are kept off-exhibit and separate from the other amphibians in the Zoo’s collection to reduce the risk of any potential pathogens affecting these toads, whose offspring will eventually be released to the wild. 

The process begins when we receive our yearly pairing recommendations and wild release schedule from the SSP coordinator. To be prepared for breeding, the toads need to be chilled and fasted for about a month to simulate the dormant period that toads undergo in their native habitat. While the toads are being chilled, animal care specialists set up a breeding enclosure for the pairs. This is a mostly aquatic habitat filled with artificial plants for the toads to rest amongst. Once their cooling period is over, the toads are warmed back up, and the recommended male and female toads are introduced to each other in this watery breeding enclosure. Within a day or so of being introduced, the male and female toads are typically found in amplexus, a breeding position where the male toad grasps the female toad with his front legs. 

To induce egg-laying, and to ensure the toads are breeding on the same schedule as the toads at other zoos and aquariums, the pairs are treated with the hormone LHRH. In Brookfield Zoo’s experience, the day after this treatment animal care specialists will arrive at work to find the breeding enclosures filled with ropelike strands of toad eggs; each female toad can produce many thousands of eggs.

The eggs develop quickly in their warm water enclosures and most have hatched into tadpoles a day or so after being laid. The tadpoles grow quickly and eat ravenously. They are fed three times a day with various dried foods and blanched leafy greens. After a few days most of the tadpoles have already doubled in size, and after two-to-three weeks they begin their metamorphosis into tiny toads.


Tadpoles Head Home
After about a week, tadpoles are ready to be sent to their new home in Puerto Rico. Once the tadpoles arrive in Puerto Rico they are released into man-made pools that are monitored by PRDNER and USFWS. Once there, the tadpoles complete their metamorphosis into tiny toadlets that then hop out of the pools helping to repopulate the surrounding areas. A few tadpoles will stay behind and be raised at Brookfield Zoo to become the next generation of the zoo and aquarium population.

The release efforts seem to be making an impact. The toads are fossorial (they like to be buried or wedged deep within crevices in rock) so they aren’t easy to survey, and are most often seen at breeding pools during large rain events. Of the six release sites at which toads have been seen returning, they breed regularly at four sites and are suspected to be breeding at the other two.

Since 2016, Brookfield Zoo has sent 12,323 tadpoles to Puerto Rico to be released. The most recent group, sent in October of 2019, was our most successful release to-date with 6,024 tadpoles. Overall, SSP participants have sent over 500,000 tadpoles back to Puerto Rico, helping to safeguard this amazing species from extinction.

Written by the Brookfield Zoo Aquatics Team

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Posted: 1/3/2020 12:31:36 PM by Sean Keeley

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