The Oil Thrush was a species of thrush unique to the continent of Atlantis. Due to the lack of ground predators, the bird lost the ability to fly, having retained only small, stubby wings wholly inadequate for that purpose. It had a long, pointed beak suitable for probing the soil for earthworms. If conditions were good, it would store extra calories as fat to be used when circumstances became harder. This fat gave rise to the bird's name.
With the arrival of humans, oil thrushes were easy prey both to feed settlers (and to render their fat into fine lamp oil) but also to animals that were introduced such as dogs and foxes. The lack of previous land predators left these birds helpless as they never developed fear to such attacks and so did not flee when approached.
During John Audubon's 1843 excursion to Atlantis, he expressed his concerns that oil thrushes faced extinction much the same way as honkers, although not as quickly since they blended into the undergrowth better. This concern did not prevent him and his companion Edward Harris from shooting several birds, both for specimens and for food.
Some forty years later, Audubon's words proved correct as the honkers were extinct but oil thrushes were plentiful enough to still be on the menu at the Belvedere Hotel in Thetford. Athelstan Helms and James Walton were sharing a bird for their supper when they were interrupted by Benjamin Joshua Morris.