Context: I'm 24m, my younger sister, whom we'll call "K", is a few years younger. 

We've had this Macaw in our family for about ten years. She was originally purchased by our mom, but has always been closest to K, as well as an older sibling whom is no longer living at home. This Macaw lives outside in a large cage during the summer, and inside on a perch in a closed room during the winter. She doesn't see any interaction most days aside from feeding and changing her water, fixing the perch and replacing toys that she's broken out of boredom, and cleaning up the enormous piles of bird droppings she creates. For years my mom and I have wanted to sell this Macaw because she's messy, temperamental, and honestly living a neglected life right now. We are aware we aren't paying attention to her, and we want to find a home that will take her off our hands - but K ardently refuses to go along with this. K would like us to keep the Macaw forever, but K barely interacts with the Macaw, just like we don't.

Now today, as has happened countless times before, the Macaw flew off her perch and pooped in another part of the room which does not have floor pads laid out as under her perch. At one point I had to access this room to retrieve something, and chose not to clean up the mess at that time - she isn't my pet, and I'm taking care of our other animals as well as feeding the Macaw. I left the door open on accident, and K saw the mess. An hour later she's comes to criticize me for not cleaning up after the "family pet," at which point I tried to explain myself to her concluding in a shouting match where both our tempers rose.

Long story short, K feels that even though I'm not the bird's owner it is EVERYONE in the house's responsibility to clean up after her, no matter what. I, on the other hand, feel that since I am not the bird's owner (and neither its owner or myself WANT the bird) it is not MY responsibility to snap on rubber gloves and scrub bird poop off the floors. Am I being an asshole?