Why are there honey bees in my bird feeder?

I am not sure what your bird feeder looks like or what bird food it dispenses. Bees as well as nectar feeding birds will be attracted to a nectar feeder ( usually a suspended bottle with some kind of drinking trough attached to open end). As the nectar content drops, it is replaced by air. This is not a problem for a bird size creature. A bee is small enough to get caught into the air currents pulling it in through the bottle opening. Placing a netting like material between the trough and the rest of the bottle will prevent bees being pulled into the remaining solution in the bottle. The netting is provided by some nectar feeder manufacturers, otherwise a piece of stocking will do.