Camouflage, or crypsis as it is sometimes called, occurs when an animal is colored to match its surroundings. Frogs use camouflage to avoid predators while they sleep, call and feed. Frogs use cryptic coloration that fits their habitat and lifestyle, with canopy species tending towards greens, trunk-dwelling species using brown and gray shades and forest floor dwellers incorporating a variety of browns, reds and black.
Hiding from Predators
Frogs are sought by a variety of predators. Snakes, fish and birds are among the most prominent predators of frogs, and hiding from all three requires different techniques. Birds are visual hunters, and play a major part in the color evolution of some frog species -- camouflage coloration is especially vital to avoid avian predators. Snakes hunt primarily by olfactory cues, though a few snakes use vision effectively. Nevertheless, snake vision is much less acute than the vision of birds, and hiding from the eyes of a bird is much more difficult than hiding from the eyes of a snake. Fish use both chemical and visual cues to find food, and frogs use camouflage and avoidance to stay safe from aquatic threats.
Color Changing Capabilities
Some frog species are noted for being able to change their color and pattern. Gray tree frogs (Hyla versicolor) are known to go from green to gray or brown in a matter of seconds. Barking tree frogs (Hyla gratiosa) not only change their colors, but can display dark spots or a unicolor skin to help camouflage. Frogs use their color changing ability to thermoregulate to some degree, being darker when the weather is cooler -- camouflage may be an ancillary benefit.
Extremely Cryptic Species
Some frogs are better camouflaged than others, and depend more heavily on camouflage as a defense. Many of the small species of North American frogs in the genus Pseudacris, known as chorus frogs, are extremely cryptic as they hide from owls and other birds in the reeds surrounding a pond. Green tree frogs (Hyla cinerea) blend well with the tree canopy as they sleep away the day. The mottled and muted earth tones of the American toad (Bufo americanus) make them all but invisible on the forest floor, while submerged Surinam toads (Pipa pipa) look much like dead leaves, fluttering gently in the murky water. The bird poop tree frog (Theloderma asperum) wins the award for creative camouflage; rather than blending in with leaves or bark, this small Asian species escapes notice by looking like bird droppings.
Some frog lineages have jettisoned the entire notion of crypsis -- instead of trying to avoid a predator’s gaze, they seek to stand out in the environment through bright colors and contrasting patterns. Poison dart frogs sequester alkaloids from their invertebrate prey, which makes the frogs’ skin secretions toxic to predators. The frogs use their bright coloration to warn predators of theses poisons, a process termed aposematism. Other frogs hedge their bets and get the best of both approaches. Gray tree frogs are well camouflaged along their dorsal and lateral surfaces, but when they flee a predator, orange or chartreuse color patches are visible along their legs. Termed “flash” markings, these are found in a variety of frog species and can serve to startle a predator or warn of a frog’s toxic properties.
- Amateur Entomologists' Society: Definition of Crypsis
- Eukaryon: Effects of Dietary Specialization on Chemical Defense of Poison Dart Frogs
- California Academy of Sciences: Rainforests of the World
- The Featured Creature: Bad Day? At Least You’re Not a Bird-Poop Frog!
- HerpNet.net: Eastern Grey Tree Frog (Hyla Versicolor)
- The American Naturalist: Poison Frog Colors Are Honest Signals of Toxicity, Particularly for Bird Predators
- Animal Diversity Web: Pseudacris Crucifer
- Animal Diversity Web: Hyla Cinerea
- Journal of Hepetology: Cryptic Behavior in Juvenile Toads
- Amphibians and Reptiles of North Carolina: Barking Tree Frog