I had lots of them in April as well. They emptied my feeder a couple of weeks ago but I didn't have a chance to fill it until this past weekend. Usually, I use the nectar I get at Mt. Hardware, but I ran out and wanted to fill it so used the sugar water recipe. Then I couldn't find anymore red food coloring, so I just used the closes I had which was purple. It's Wednesday and finally saw one come back this morning. I guess it took them a few days to find out that I've refilled it.
By this time of the year, they're lined up waiting for their turn. Maybe they went on vacation somewhere. I'm interested to see if Wildman had a decline in hummer visitors.