When choosing a bird cage, bigger is not only better – it's best. Obviously, large birds, such as parrots and macaws, need more room than smaller canaries and finches, but they all need space to stretch. The cage should be two to three times the bird's wingspan and three times its length, from head to tail. The cage should be large enough for the bird to open and flap his wings from several places within the cage. Other factors determine the most comfortable house for your bird. For example, since canaries like to hop from perch to perch, they need a wider cage to make them comfortable. Long-tailed birds, like macaws, need room to stretch their wings, so they need a taller space.
For more information, please read Getting the Best Cage For Your Bird.