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Quakers are a smaller breed of parrot, but because of their active nature, they do best with a roomy cage.  An 18” x 18” x 18” cage should probably be the minimum size for your bird, but also consider safety and security features.  Quaker parrots are known for being escape artists, so make sure the bars on the cage are not too far apart, nor at the same time narrow enough that a curious quaker can get its head stuck between them.  ⅝-inch spacing between bars is a good reference point. Likewise, to counteract their curiosity and escapability, choose a gate that swings open (not a guillotine-style gate that a quaker may be able to lift up only to have it become a trap).  Quakers have been known to figure out how to unlatch a gate, so consider a lock as well. A repetitive daily diet of bird food pellets not only lacks the diversity to provide proper nutrition, it may also cause boredom (and thus a lack of eating) in birds like quakers.  Make the pellets part of the diet, but also mix in a variety of fruits and vegetables, and occasional seeds and nuts. Avoid feeding birds avocados, however, as this can be toxic to them; also skip chocolate, caffeine, and alcohol. Birds are messy — there is no way around it.  In addition to droppings, quakers will strew food scraps, destroyed toys, and bits of anything else they can get their beaks on throughout the cage and on your floor.  Give the cage a quick cleanup daily, removing large bits of junk and replacing the newspaper liner (you may want to subscribe to a daily paper if you’re going to be a bird owner). Each week, give the cage a more thorough cleaning, scrubbing down the bars and such. You may want to place the cage over an easier-to-clean floor surface, such as tile or hardwood rather than carpet. Take your quaker for annual checks (and more as warranted) by a veterinarian, preferably one with a bird specialization.  Beak, claw, and feather health should be areas of particular focus for you and your vet, as problems in these areas are often indicators of larger issues.  Quakers may be more susceptible to fatty liver disease, so don't let your bird become overweight.  Limiting seeds and other high-fat foods may be necessary.  Talk to your vet if you are concerned. Feather plucking is another disorder that can be common among quakers, and can have physical or behavioral causes.  A good avian vet can help you with this issue as well.
Buy the right cage. Provide a diverse diet. Expect messes and frequent cleaning. Find a good vet.