Its a pity that animal men up sticks to elven civilisations so readily now, rather than stay in the crude settlements they live in naturally and occasionally harass your fortress livestock by killing it (& anything else they can handle) before dragging it off the map to cash it in, or at-least that's how i remember it. Then again i can't recall encountering a animalmen settlement (a collection of huts with a announcement) from fortress mode recently in the last couple of versions even in a abandoned state, so unless its been turned off or im just very poor at finding them they might as well not exist.
Its impossible to detect them before they emigrate via worldgen (because they are a hidden embark feature that doesn't appear on the map), though you can get a feel for how many animalmen are joining the elves on account of the 'Regions' part of the legends screen informing you of their point of origin before they join the elven civilisation. (maybe ill use that to try and track down some evidence of them being there soon)
In some strange way i never really understood how that worked, if i suddenly race-swapped today or put up the raws relatively close to elves (it might be a hardcoded thing with how animalmen work or purely worldgen) would i just get legions of animalmen turning up at my door demanding residency or equipped in their own or elfish crude goods rushing in? (sounds like science potential)
Running any kind of elven tavern is pretty much 200% impractical without extensive modding so i dont think id even get the opportunity to find out without dedicating time. Prior to the tavern update i only ever settled once (maybe twice) on a animalmen site above ground, and it was certainly tense, because they saw you, and you saw them constantly edging closer then backing off like annoying neighbours behind your back trying to do the worst stuff without being caught early on.
The only animalmen i usually see nowadays are tavern visitors and completely naked
hamster and rat men vermin running in from time to time as a 'animal spawn'. I miss it honestly.