What this actually means for the structure of the foot is a question that is still being researched today. It would seem that an accessory navicular is commonly related to pes planus. Frederick Kidner, in 1929, first theorized that the presence of an accessory navicular could be the cause of pes planus.
Successful as they are, Eastern Gray Squirrels live only 11-12 months on average, but some individuals have survived more than ten years in the wild. Factors affecting survival include the severity of winter, abundance of food, and parasites.
An African Grey that is forced to subsist on a seed-only diet may be lucky enough to live as long as 15 years; but one that is given a balanced diet has the potential to live 40 to 60 years, or longer. Improper nutrition can be the underlying cause of other problems, such as allergies and feather picking.