Why don't these bees be-a-buzzing?

Out walking the dog over the last few weeks, I’ve noticed that there are single bees of all sizes here and there on the ground. Most of them are dead, but on the odd occasion they have still been alive, but not looking in very good shape.

I’ve heard about these problems bees have been having throughout the world and I’m wondering if what I’m seeing is symptomatic of this, or a natural part of what happens to bees that I’ve just never noticed before?