Though generally avian in physiology, they had several mammalian characteristics. Female treshers also suckled their young on milk. For the first four months of their life, tresher chicks had fleshy mouths for suckling from their mothers. As they matured, this became a hard beak. Unlike most birds, they had toothy beaks and bone ridges set in their tail feathers.
Ungainly on land, treshers were graceful and swift in flight. Their keen eyesight allowed them to spot prey from high above the ocean's surface and swoop down on their target with deadly accuracy. They could reach speeds of up to 160 kilometers per hour in a dive, stopping just above the surface to snatch their prey in their talons.
Treshers mated for life, and fiercely defended their nests, chicks, and mates. While they tended to avoid contact with humanoids, treshers could attack trespassers with beak, tail, or talon. A full-grown tresher could even seize a humanoid-size creature and fly with it for at least one hundred meters. Even tresher chicks had a nasty bite.
Unfortunately for the treshers, they were sensitive to pollution. Heavy metals or industrial chemicals in their environment weakened their eggshells, led to tresher chicks in polluted regions being stillborn. Treshers were also the target of hunters, since tresher meat was in demand by some of the galaxy's gourmets, and their colorful feathers were also considered valuable. The possible extinction of the treshers would have been disastrous for the ecology of Tinallis, as the blue-ringed sea crab population was only kept under control due to predation from treshers.
In response, the Tinallian government made treshers a protected species, making it a criminal offense to hunt a tresher or to take an egg or live specimen. Tresher poaching continued, however. In fact, some off-world biologists violated the law in order to obtain chicks or eggs which could be raised in captivity to establish a safe population. One biologist on Deminol offered 10,000 credits for a single tresher egg. The hunter she hired, Fendel Ramison, was ultimately unsuccessful.