What thickness, size, and quality plywood is required for an aviary floor?
A standard residential flooring panel is combination subfloor-underlayment with a 16 inch span rating and with tongue and groove edges. This is usually a 5/8 or 19/32 inch thickness. Thus the joists are spaced on 16 inch centers. The joist size cannot be determined from the information provided.

That is just a starting point. Bird droppings are very corrosive and can quickly degrade such floor panels. You should not only consider a thicker panel, but some sort of topping much more resistant to bird droppings.