Some deficiencies, particularly mineral deficiencies, can cause overgrowth of the nails and beak. Excessive nail growth is seen in Severe Macaws a lot, and it is likely they are a species that needs one particular supplement more than other parrots. They are a species seen at the Manu clay licks, and recent studies have suggested the clay provides salt or other minerals that are important to the species that frequent them.
The perches could also be a factor. I’m not sure what you mean by fabric perches unless you are referring to rope perches? Parrot should have several perches made from a variety of materials and made in different or varying sizes. This not only helps to exercise the feet, but is can help with the nails and help keep the feet cleared of dead cells. One fabric perch is all your bird should have. Natural wood branches are the best choice because they are not all one size. Manzanita is recommended for a Severe Macaw because of their powerful bite.
There is no single schedule for nail trims. It varies by bird and what they eat and what they stand and climb on. Most nails get too sharp rather than too long. A grooming perch can keep the nails from getting as sharp in between trims. You want the concrete or textured type, but not one where the surface can come loose, such as a sandpaper or gravel coated perch. The grooming perch should not be the bird’s primary perch. It’s best to place it where the bird uses it to step to another perch. It should be a diameter where the nail tips touch the perch – so generally larger than the other perches. These perches are most effective after a nail trim, and not to dull nails that are already too sharp.
Thank you for asking Lafeber,