Question
My trees are dropping small branches through out the winter.  What would cause my trees to lose very small branches?

Answer
Check the branches and if they seem to be cut off clean then this is a twig girdler or twig pruner. This is an insect (beetle) that lays its eggs in the twig near the tip and cuts the twigs off letting it fall to the ground. The eggs hatch and the larvae grow in the twig on the ground and emerge to lay more eggs. the population will vary each year due to the number of larvae that will not complete the life cycle. The control is during the fall or winter, gather fallen branches from the ground and prune suspected infested branches still in the tree and burn them.
Here is a web link to more information on these insects and pictures of the twigs cut

http://extension.missouri.edu/explore/agguides/pests/g07276.htm