It is said that the parander changes its appearance when it is afraid and, when it hides itself, takes on the likeness of whatever is near – a white stone or a green bush or whatever other shape it prefers.

Source: The Aberdeen Bestiary.

Latin name: Parandrus
Other names: Tarandrus, Tharandus
A beast that can conceal itself by changing its appearance

General Attributes
The parandrus is a beast from Ethiopia that can change its appearance, so that it can conceal itself by taking on the appearance of its surroundings. It is colored like a bear, but is the size of an ox and has long hair. It has the head of a stag with branching horns, and has cloven hoofs.

Sources (chronological order)
Pliny the Elder [1st century CE] (Natural History, Book 8, 52): Pliny mentions a beast from Sythia called tarandrus (usually translated as reindeer or elk) that can change color.

Source: Medieval Bestiary.

all the animals of Satan’s bestiary, assembled in a consistory and set as guard and crown of the throne that faced them, singing its glory in their defeat, fauns, beings of double sex, brutes with six-fingered hands, sirens, hippocentaurs, gorgons, harpies, incubi, dragopods, minotaurs, lynxes, pards, chimeras, cynophales who darted fire from their nostrils, crocodiles, polycaudate, hairy serpents, salamanders, horned vipers, tortoises, snakes, two-headed creatures whose backs were armed with teeth, hyenas, otters, crows, hydrophora with sawtooth horns, frogs, gryphons, monkeys, dog-heads, leucrota, manticores, vultures, paranders, weasels, dragons, hoopoes, owls, basilisks, hypnales, presters, spectafici, scorpions, saurians, whales, scitales, amphisbenae, iaculi, dipsases, green lizards, pilot fish, octopi, morays, and sea turtles.

Source: The Name of the Rose by Umberto Eco.