There are many things that can cause overgrown or abnormal beak and nails in pet birds.
The three most common are:
1. Not having toys/perches to rub beaks or grind nails on
2. Nutritional problems (not enough vitamins in their food)
Any bird with an abnormal beak or overgrown nails should be checked by a veterinarian to ensure they are healthy, our vets can also trim the nails and overgrown beaks of birds of any size.