Milkweed starting to bloom but no Monarchs

We have several large colonies of milkweed on our farm ... partially a result of bush-hogging around the colonies the last four years and allowing them to grow and expand.  Most of these colonies have well over 100 plants.  One these colonies is in the small field behind our house.

The common milkweed is just beginning to flower this week.  With all the rain, the plants are robust with lots of large umbels (flower clusters).  The butterfly plants are a little further behind the common milkweed.

Although there is an abundance of Eastern Tiger Swallowtails and dozens of Great Spangled Fritillary ... still no Monarchs or milkweed larva.  I will keep looking.