Ok... 10 seconds later and I'm back for another response.. I can't do a test on the actual owl... And even if i could, i don't know what size you're trying to scale it to...
But i did a test with some simple rectangles... It looks like while the Object > Transform > Scale tool does seem to have a lower limit.... The transform panel does not. You can select your artwork and then go to your transform panel, make sure proportions are locked, then click inside the width or height input boxes and type "*.1" to scale the art to 10% without any "artwork too small" errors. I tried everything i could think of to break this and I couldn't do it.. There is actually a lower limit to the size, but it's for the size of all of the selected artwork.. So let's say you just have a square that is 10pt x 10pt. you can select that square and then use the transform dialog to scale it (using a percentage by multiplying the current value by a decimal, or by typing in an absolute width/height), you can scale it as small as 0.0001pt. If you attempt to scale it any smaller than that, the UI will simply show "0" for the dimension.. However, this limit appears to be applied to the entirety of a selection rather than to the individual elements therein... So, if you duplicate your 10x10 square 200pt to the right, then duplicate both of those 200pt down, you'll have a square of squares. one square in each corner. if you select all of these squares, you can scale the whole set down to .0001pt as well, effectively making each individual square mind numbingly miniscule, with no error.
I even tested out saving the file thinking that maybe just because it didn't throw an error when scaling the art.. maybe illustrator would complain when trying to save it... No problems there. And even opening the file back up, all the art is there just like it was when i saved, so small you can't even see it on the screen. It appears also that you can repeat this process indefinitely... Or at least my several attempts to copy each scaled group and then scale everything again didn't find a limit.. Interestingly, if you look at any individual shape in the UI after scaling it this way, the transform panel shows 0 for the height/width.. But if you analyze the dimensions with javascript/extendscript, you get a tiny tiny number written in scientific notation (3.46726665156893e-7). So even though the art is too small for the UI to display, and even too small for the UI to display a dimension, it's still there in the file with no errors.
Disclaimer: I'm not attempting to say this is the best way to handle this or the smartest way... It's just one possible way to do it. But it's not ideal. Like most non-ideal things in life, they're not gonna kill you. Doing it this way isn't going to prevent you from doing whatever project you're trying to do... But I did want to point out for posterity that this is an inherently inefficient method of doing this. Even if you can't see a piece of artwork in your file... It still has anchor points. It still has color data. It still has position data and height data and width data etc. Which means that any time you zoom/scroll/pan/open/save the document, Illustrator has to do all of the vector math to handle those shapes, even if they're invisible to you.
Again, without access to the specific vector artwork you're using, i don't have much to go on.. I don't know if there's one or two shapes that become too small when you scale it.. Or whether there are hundreds or thousands. If it's one or two.. you will never notice a difference. If it's hundreds or thousands, you might find yourself getting hypnotized by the spinning wheel of doom while you wait for a bunch of invisible art to be calculated.
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