The number for a caique
Choose bar spacing of three-quarters of an inch for a caique, and read that figure as a maximum, not a rough guide. Both caique species kept as pets, the black-headed and the white-bellied, are stocky, strong parrots of about 9 inches, but their heads are smaller than their chunky bodies suggest. A gap that looks harmless against the bird's body can still admit its head, and a parrot that pushes its head between bars and cannot reverse out can injure itself badly in its panic. Three-quarters of an inch lets a caique climb, grip and look out comfortably while keeping the head safely on the inside of the cage.
Why narrower is not automatically better
Owners sometimes assume the tightest spacing must be the safest, but spacing far below the recommendation creates its own problems for a caique. Very closely spaced bars are usually thinner bars, and a caique is an exceptionally physical bird: it hangs by one foot, swings, wrestles toys, and works the bars with a strong beak, so flimsy wire flexes, paint chips and welds tire. A cage built for a much smaller bird also tends to be a smaller cage overall, and a caique needs generous room for its non-stop play. The safe combination is spacing at three-quarters of an inch on bars stout enough for a bird that treats its cage as climbing equipment, inside a cage roomy enough for that energy.
Measure the whole cage, not one panel
Bar spacing is only as safe as the widest gap anywhere on the cage, and the main flat panels are rarely the offenders. Check the corners, where curved or joined sections can open up wider spaces, the gaps around food-cup doors and the main door frame, and any place where a decorative scroll or a bent bar creates a wedge shape. Wedges are especially risky because a head slips in at the wide end and locks at the narrow one. Run a simple test before the bird moves in: if a three-quarter-inch marker, or your measured gauge, passes anywhere it should not, or a gap visibly widens when the bars are pressed, that cage fails for a caique even if its label quotes the right spacing.
A caique will test your choice
Spacing matters so much for this species because a caique interacts with bars more than almost any comparable parrot. It climbs the sides using beak and feet together, hangs upside down from the roof bars, and squeezes itself into improbable positions while playing on its back with a foot toy. That athleticism is exactly what you want to encourage, so the cage has to be safe under full-body, all-day investigation, including the bird pushing at bars from odd angles while hanging. Inspect the cage monthly for bars bent out of true by chewing or by a dropped heavy toy, and straighten or retire panels whose spacing has crept wider than it was on delivery day.
If a head does get stuck
Stay calm and act at once: a trapped caique can injure its neck and eyes within moments of thrashing. Support the bird's body so its weight is not hanging from its head, keep the head in the exact line it entered rather than twisting, and have a second person gently ease the bars or guide the bird back while you hold it. If the bird is not free almost immediately, or shows any swelling, eye injury, weakness or breathing difficulty afterwards, it needs an avian veterinarian as an emergency, and the cage should not be used again until the gap that caught it is found and fixed.
Bar spacing is the kind of single number a whole household ends up needing, from whoever buys the cage to whoever spots a bent panel, and keeping that three-quarter-inch figure in the bird's shared profile through Family Sharing on KinsLe means nobody has to guess it at the shop or at the cage door.