Your oranges are ready to pick when they turn a nice bright orange. The ones on the sunny side of the tree generally ripen first. If you don't get to them first, there are critters that will let you know when they are ripe. Snails leave little holes in the outside peel, rats hollow out the fruit, and squirrels carry them off, often leaving partly eaten fruit on a nearby fence. UC offers a detailed table to help identify citrus damage from insects and other pests.