Oaks have many insects throughout any year feed on them to a degree. Without seeing the insect feeding on the tree, I cannot say for certainty what has caused the holes in the leaves of the tree. The holes in the leaves do not give cause for alarm and the health of the tree should be fine. The tree is coping more with the incidents of drought we've had so far this year. This will affect the tree more than leaves with few holes. The majority of each leaf is still present (at least in pictures provided) and the tree can tolerate this with little difficulty. My suspicion is caterpillars have fed on the tree some and have grown to a life stage that is no longer feeding on the tree. Insecticides do not appear to be necessary. Caterpillars feeding on oak trees are great sources of food for the birds in the area. I recommend tolerating the insects and enjoy the birds because the tree should be fine based on the images provided.