|An Anna's hummingbird sits on a nest at Plant Depot. Photo by Paul Bersebach, OC Register|
The reduction could be for a variety of reasons, according to Monique Rea, a local hummingbird rehabilitator. There could be a change in the flowers or water or the food source – or they could have finished nesting, she says. See a slideshow of the nesting hummingbirds at The Orange County Register.