Seeing your budgie puffed up like a little ball can be endearing — or worrying. The key is whether it is brief and relaxed, or constant and paired with other signs.
When puffing up is completely normal
A budgie fluffs its feathers for lots of harmless reasons: it is resting or sleeping, preening, feeling relaxed and content, shaking its feathers back into place, or briefly warming up. A budgie that puffs up now and then but is otherwise active, eating and chirpy is usually just fine.
When puffing up is a warning sign
The concern is a budgie that stays puffed up for long periods, especially alongside other signs: sitting low or on the cage floor, tail bobbing with each breath, sleeping a lot during the day, eyes closing, not eating, or sitting fluffed and quiet in a corner. Sick budgies fluff up to conserve heat, and because they hide illness so well, a persistently puffed, subdued budgie is often genuinely unwell.
If your budgie looks puffed and off for more than a short while, do not wait and see — contact an avian vet. With small birds, hours can matter. It helps to check its droppings and its weight before you call.