The tarn, like most birds, is surprisingly light for its size, this primarily having to do with the hollowness of the bones. It is an extremely powerful bird, powerful even beyond what one would expect from such a monster.

Whereas large Earth birds, such as the eagle, must, when taking flights from the ground, begin with a running start, the tarn, with its incredible musculature, aided undoubtedly by the somewhat lighter gravity of Gor, can with a spring and a sudden flurry of its giant wings, lift both himself and his rider into the air. In Gorean, these birds are sometimes spoken of as "Brothers of the Wind".

The plumage of tarns is various, and they are bred for their colors as well as their strength and intelligence. Black tarns are used for night raids, white tarns in winter campaigns, and multicoloured, resplendent tarns are bred for warriors who wish to ride proudly, regardless of the lack of camouflage. The most common tarn, however, is greenish brown.

Disregarding the disproportion in size, the Earth bird which the tarn most closely resembles is the hawk, with the exception that it has a crest somewhat of the nature of a jay's.

There are three types of tarns...common, war and racing tarns; each very different from the other, not simply in the training, which does differ, but in the size, strength, build and tendencies of the bird.

Some tarns are bred primarily for strength and are used in transporting wares by carrying basket. Usually these birds fly more slowly and are less vicious than the war tarns or racing tarns.

The war tarns, of course, are bred for both strength and speed, but also for agility, swiftness of reflex, and combative instincts. War tarns, whose talons are shod with steel, tend to be extremely dangerous birds, even more so than other tarns, none of whom could be regarded as fully domesticated.

The racing tarn, interestingly, is an extremely light bird; two men can lift one; even it's beak is narrower and lighter than the beak of a common tarn or war tarn; it's wings are commonly broader and shorter than those of the other tarns, permitting a swifter take-off and providing a capacity for extremely abrupt turns and shifts in flight; they cannot carry a great deal of weight and the riders, as might be expected, are small men, usually of low caste, pugnacious and aggressive.

Racing tarns are not used by tarnsmen in war because they lack the weight and power of war tarns; meeting a war tarn in flight, a racing tarn would be torn to pieces in moments; further, the racing tarns, though marvellous in their particular ways, lack the stamina of the common tarn or the war tarn; their short wings, after a flight of perhaps only fifty pasangs, would begin to fail; in a short distance dash, of course, the racing tarn would commonly be superior to the war tarn.