Discover remarkable toads and frogs making a splash at locations throughout the Zoo and Safari Park
BY Eston Ellis
Photography by Ken Bohn
From big, familiar California natives to tiny, endangered South American rain forest dwellers, frogs and toads are a varied bunch. Some are wildly colorful and others are well camouflaged. With skin as slick as a diver’s wet suit (in the case of most frogs) or bumpy and seemingly wart-covered (in the case of most toads), these species are known for their spectacular jumping ability, calls ranging from deep “ribbets” to high-pitched chirps, and bulging eyes that give them a wide field of vision. The word “frog” can apply to any frog or toad species, since both are members of the Order Anura (meaning “without tail”)—but while all toads are frogs, not all frogs are toads.
It’s Not Easy Being a Frog
Toads and frogs are ectothermic, using the sun to regulate their body temperature. They depend on warmth to become active, and when they get too hot or too cold, they may go into a burrow or find shelter in tree hollows or under rocks. In cold weather, frogs and toads become sluggish until the weather gets warm again.
Frogs start as tadpoles: they emerge from eggs with round heads and fishlike tails. “In this aquatic stage, they have gills for breathing underwater,” said Rachael Walton, senior reptile keeper at the San Diego Zoo. “But soon, they undergo a complete transformation.” During the tadpole stage, they typically eat aquatic plants and algae, although some species eat other tadpoles. As they grow, they develop legs, and their mouth parts change. Their tails are eventually absorbed into their body, they lose their gills, and they develop lungs. When the metamorphosis is complete, the tadpole becomes a frog or a toad, breathing air, hopping on land, and eating live prey—usually insects.
Most people have seen photos of frogs using their long, sticky tongues to reach out and catch flying insects in midair. “But did you know they actually use their eyes to push food from their mouth into their stomach—swallowing with a big, forceful blink?” Rachael asked. “Frog species with teeth may use their teeth to grab prey, but they still swallow their prey alive, and it dies in the frog’s stomach acid.” She added that “Frogs feed by motion. They are not interested in anything that is not moving.”
There are about 5,532 known frog and toad species worldwide, and 412 of them are categorized as Critically Endangered on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Another 1,749 frog and toad species are listed as either Threatened or Extinct in the Wild. “Frogs are indicator species, and observing frogs gives you an idea of the health of their ecosystem,” Rachael said. Frogs have a permeable layer of skin, with mucous glands to keep it moist—they breathe through their skin as well as their lungs. For that reason, frogs are especially vulnerable to waterborne toxins, ranging from industrial and agricultural chemicals to waste pharmaceuticals in sewage. “Where chemicals have gone into the watershed, you may see frog populations decline long before you notice other effects,” Rachael said.
Known frog and toad species (according to IUCN)
Home Sweet Habitat
Exhibits at the Zoo and the Park replicate features of each species’ wild habitat, from temperature and humidity levels to lighting and foliage, to still ponds and rushing streams. “Some species need running water, and some need access to calm water that is suitable for laying eggs,” Rachael said. “We use reverse osmosis water filtration for all our exhibits, so our frogs won’t come in contact with minerals they would not find in their original habitats.”
Guests may see frogs exhibiting natural behaviors, including a unique courtship “dance” called amplexus. “It looks like one frog is giving the other one a piggyback ride,” Rachael said. When a female frog comes close to a male, he wraps his arms around her back and hangs on tight. Then, he waits for her to release her eggs, so he can fertilize them. “He has to wait for her—and it can be a long piggyback ride while he’s waiting; maybe weeks or even a month.” After she lays the eggs and he fertilizes them, the male (depending on the species) may guard the eggs until they hatch.
FINDING FROGS AT THE ZOO AND SAFARI PARK
ZOO REPTILE WALK—NATIVE SPECIES BUILDING
Colorado River toads (photo above) were once a familiar sight in Southern California. This toad’s mottled brown coloring helps it blend into chaparral or desert surroundings. Unlike most frogs, toads do more walking than long-range jumping—and the Colorado River toad has a built-in defense strategy to deter predators. “If the Colorado River toad gets stressed out or threatened by a predator, it can emit a little bit of toxic fluid from a gland behind its eye, called the parotid gland,” Rachael said. The fluid can either repel or sicken any potential attacker.
Frog and toad species that are Critically Endangered
Behind the Scenes
Frogs also live behind the scenes at the San Diego Zoo Institute for Conservation Research, where endangered mountain yellow-legged frogs are raised for release into Southern California mountain streams, in partnership with the U.S. Geological Survey. Before these frogs are released, they receive a vaccine that protects them from the chytrid fungus. Frogs face many threats worldwide, including habitat loss to development and agriculture, water pollution, and disease. The major cause of declines in frog populations is chytrid, a pandemic fungus that is killing frogs in large numbers, Rachael said. Chytrid fungus lives in water, infecting frogs by covering their skin so they can’t breathe or absorb water—and infecting tadpoles, covering mouthparts and preventing them from eating. The Amphibian Disease Laboratory at the San Diego Zoo Institute for Conservation Research currently provides testing for two types of chytrid fungus to zoos, wildlife agencies, and researchers, to encourage widespread monitoring of frogs and help prevent the further spread of chytrid.
Frog life span in years, depending on species
While you will find many frogs and toads at the Zoo and Safari Park, don’t be surprised if you spot one in your own yard, too. While frog populations are decreasing worldwide, there are still healthy numbers of them in many areas—whether conditions are rainy and lake levels are high, or the weather is hot and the ground looks sunbaked and dry. “If you find a frog in your backyard or on a hike, leave it there,” Rachael advised. “Even though their local habitat may seem dry, there is a lot of water that frogs can use, from puddles to tiny streams or small ponds.” Frogs help control insect populations, and their familiar calls provide welcome background music for dreamy summer nights. And as indicator species, their continued survival provides hope for the future of their ecosystems—and our planet.