A. We will always see fluctuations in the number of hummingbirds coming to feeders in some portion of North America every year. But based on past experiences and the lack of any reports of "catastrophic" events that would have effected hummingbird populations, we believe the lack of activity you might be experiencing at your feeders is most often tied to weather and it's impact on the abundance and quality of the plants that provide natural nectar sources.
In areas experiencing prolonged, multiple year drought, we have seen much reduced activity at feeders as hummingbirds continue their migration to avoid areas that are almost completely devoid of nectar plants. They will not take a chance on nesting in areas with such extreme conditions. In contrast, once established on their breeding ground during a normal weather year, a short term summer drought seems to drive hummingbirds to feeders as their sources of plant nectar begin to dry up.
Due to favorable weather conditions this year, the Eastern portion of the US has been experiencing one of its best growing seasons in years. The widespread abundance of nectar plants is providing a tremendous natural food supply for hummingbirds which reduces their activity at our feeders. It also allows them the advantage of being able to spread out their breeding territories into areas that may not have been able to support them in less favorable years. So there may be fewer hummingbirds at any given location than in previous years, but the overall population is stable...just distributed over a wider area.
During the height of the nesting season, female hummingbirds are hard a work at the nest - incubating, brooding, feeding 1-2 nestlings. Throughout that process, we typically see a little less of the adult females. But that changes once the young fledge, when females and young make frequent visits to quality nectar sources. Make sure your feeders are clean and the nectar is fresh so that your feeders are amongst the nectar sources they choose to visit!
The majority of this material was provided by WBU Chief Naturalist, John Schaust.