Bronze headed borer
Last summer, birch trees around the metro area seemed to be hit especially hard by the bronze birch borer. The drought probably stressed the trees, making them more susceptible to attack. Unfortunately it can be a losing battle once a tree is attacked. If your trees are not too far gone, maintain their vigor by keeping them well-watered throughout the hot summer and mulching around the base to keep the roots cool and moist. This will help them resist borer damage. If it looks like a lot of the tree crown is already dead, it may be too late and the tree should be removed.
Here are some links to help you better assess whether your trees can be saved, and what to do: