It might be their nesting season, depending on where you live/which breeds are native to your area. The males will be making a few appearances at the feeders, but the females are keeping a close watch on the nest (which they won't make near a regular feeding zone) and since the newly hatched young need more protein than sugar, the mama's are busy catching bugs. Once the chicks leave the nest, you''ll see a large uptick of hummers.