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. [caption id="attachment_125365" align="aligncenter" width="1200"] TRANSFORMERS
Frogs go through a remarkable metamorphosis, starting out in the water as eggs, from which tadpoles with gills emerge. The tadpoles develop legs and more frog-like features as they grow, develop lungs, lose their tail, and begin living out of the water.[/caption] 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. [caption id="attachment_125367" align="aligncenter" width="1200"] HUNGRY EYES
Frogs use their eyes for more than just spotting their next meal. A deliberate “blink” of those big eyes applies enough pressure on top of their mouth to help swallow a large mouthful of food, pushing it into their stomach.[/caption] 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.” [caption id="attachment_125368" align="aligncenter" width="1200"] INDICATOR SPECIES
Frogs breathe through their skin as well as their lungs. They are often called “indicator species,” because their disappearance can indicate the presence of toxins in their habitats.[/caption] 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.

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. [caption id="attachment_125371" align="aligncenter" width="1200"] ZOO REPTILE WALK—AMPHIBIAN BUILDING

Poison frogs have colorful skin that warns potential predators to stay away: eating them, or even touching their skin, could prove fatal. Here, guests can see vivid-hued green and black, splash back, bumblebee, black-legged, and dyeing poison frogs, as well as golden mantellas. They are tiny, but visitors can often see them moving around and climbing, or relaxing in moss at the bottom of their exhibits. You might also notice a little coconut husk “hut” in the poison frogs’ exhibits, where these frogs lay their eggs. “One question we get asked a lot is whether we handle the poison frogs,” Rachael said. “In their wild habitats, their skin can secrete powerful toxins, which are built up through what the frogs eat, such as venomous insects and biting ants. However, poison frogs at the Zoo do not have toxins in their skin—they eat crickets and fruit flies, which do not contain toxins.”[/caption] [caption id="attachment_125372" align="aligncenter" width="1200"] Red Sambava tomato frogs have predator-discouraging tomato-red skin, but no poison. “Tomato frogs are not dangerous in any way, but their color tells predators ‘don’t eat me,’” Rachael said.[/caption] [caption id="attachment_125373" align="aligncenter" width="1200"] Bornean eared frogs get their name from distinctive ear-like ridges on each side of the head. On hot days, you might find the normally nocturnal Bornean eared frog moving around in its exhibit. This tan-colored frog sometimes puts on its own bubble show, creating a nest for its eggs that looks like a cluster of bubbles. They build their bubble nest above a body of water, so that when the eggs hatch, the tadpoles drop in and start swimming.[/caption] [caption id="attachment_125374" align="aligncenter" width="1200"] Tree frogs, like the splendid (seen here), milk, and White’s, have disc-shaped toe pads that are sticky, providing good traction for climbing. “Splendid tree frogs come from Australia, where it’s hot—and they spend a lot of time sitting out on broad leaves in their exhibit, basking in UV light,” Rachael said. Related to the White’s tree frog, the splendid tree frog has bright green skin with a waxy, protective coating.[/caption] [caption id="attachment_125375" align="aligncenter" width="1200"] Mossy frogs are aptly named camouflage experts, blending perfectly into their surroundings. This frog’s moss-like green and brown coloration and its bumpy skin help it seem to disappear among moss and rocks in its wild habitat.[/caption] [caption id="attachment_125376" align="aligncenter" width="1200"] Panamanian golden frogs are really a type of toad. In its native Panama, this colorful yellow-orange and black species is extinct in the wild. “Ours are ambassadors for their species,” Rachael said. The Zoo maintains an assurance colony of Panamanian golden frogs, and more than 60 have hatched at the Zoo. Working with other accredited facilities to help increase the population of this species, our hope is to eventually return these toads to their original habitats.[/caption] [caption id="attachment_125377" align="aligncenter" width="1200"] ZOO—ELEPHANT ODYSSEY

California native western toads can be found in another part of the Zoo—by visitors who are both eagle-eyed and lucky. “On a cool morning, you can sometimes see western toads in the pond exhibit at Elephant Odyssey,” Rachael said. “Look for them near the terra-cotta half pot and grasses. We have 11 of them, but spotting one is like finding a golden ticket!”[/caption] [caption id="attachment_125378" align="aligncenter" width="1200"] SAFARI PARK—NAIROBI STATION

African bullfrogs, the largest amphibian species in southern Africa, can grow up to 10 inches in length. They have a reputation for eating anything they can catch that will fit in their mouths, including other frogs. They breed after heavy rains—females lay eggs in temporary pools of water, males protect the emerging tadpoles from predators, and it takes only about three weeks for the tadpoles to metamorphose into frogs. These frogs spend the hot, dry season burrowed underground.[/caption] [caption id="attachment_125379" align="aligncenter" width="1200"] White's tree frogs are native to Australia and New Guinea. These eye-catching green frogs can survive in seasonally wet or dry forest habitats—thanks to their ability to secrete a waxy substance, which they use to protect their skin from drying out. In the dry season, they hide in tree hollows wrapped in a cocoon formed from shed skin and mucus. Unlike most tree frogs, their eyes have horizontal pupils instead of vertical ones.[/caption]

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.

And...Your House

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.