There was a drought last year so it might have affected the trees this year.
Too bad about the squirrels. There are still way too many.
“But last May, when the oak trees would have been busy flowering, coating cars and sidewalks with a thick dusting of golden pollen, the National Weather Service logged 10.6 inches of rain at Reagan National Airport — three times the normal amount, making it the third wettest month on record since 1871.”
That's probably the answer right there. Those tree rats could use a good thinning out anyway.