Abbreviated LTTS or LttS. A pretty small mod, niche little thing that really doesn't add a ton but might prove nice anyway. Files go in <DF install directory>/raw/objects except for the file titled "README". This is a changelog of sorts, though I've not been great about actually adding things to it.

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This mod adds a new race, the thundath, who are descended from a new megabeast, the thunderbird. As might be expected, the thundath are substantially-sized birdfolk, quite a bit larger than the average human. Some possess the ability to shock foes in melee range, briefly paralyzing them, an ability that thunderbirds also have. Thundath should be able to fly, but fortress mode has incredibly wacky pathing for intelligent fliers, so it's disabled by default. Thundath are capable of making legendary artifacts, and are always at least competent in biting, kicking, fighting, dodging, and observing enemies. They have taloned fingers instead of fingernails, and live an extremely long time, generally able to reach over a millennium of age.
Female thundath lay eggs. Thundath are generally quite monotonous in color, always being mainly gray.
Thunderbirds themselves are always at least talented in biting, kicking, fighting, dodging, and observing enemies. In this mod they are fairly similar to rocs, possessing similar size and habits. Their ability to shock foes who enter melee range makes them quite dangerous, however.
The thundath have two things unique to them: skyforged metal (an alloy of steel, bronze, silver, gold, bismuth bronze, rose gold, sterling silver, nickel silver, black bronze, electrum, and billon; its properties are the average of all these, as is its value) and skyforged constructs, which are golem-like humanoid beings made from the aforementioned metal.
Thundath settle mountains and surrounding areas, building towns. They have their own language - one word of which is quite intentionally 30-something letters long, so thundath can occasionally end up with very long names. They are capable of taming animals that aren't considered "exotic". If you have contact with a civilization of thundath, they send caravans in the summer.

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I regrettably do not know a lot about Native American culture, which I am aware the thunderbird comes from. If you are yourself Native American and something in this mod causes you offense, comment or send me a PM on the Bay 12 Forums (where I go by IncompetentFortressMaker) describing the nature of said offense. I'd prefer not to cause trouble; if there's a problem, please let me know what it is so that I can hopefully do something positive about it.