When I lived Sierras, Broad-tailed Hummingbirds started arriving in early April when there was still snow on the ground.  There were no flowers in bloom and there were no insects flying around.  I would rush to put up feeders but didn't understand what brought them so soon.  

When the days begin to lengthen, sap starts rising up into the trees to supply food for the summer growth.  This is when the sapsuckers arrive and there is evidence that many hummingbirds follow their migration pattern.  Sap is composed of sucrose, water and amino acids, so it is a well-rounded food source for the early arriving hummingbirds.

Photo by Bob Bowers

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Most hummingbirds fuel their energy needs by sipping nectar from nectar-producing flowers.  The flowers and the hummingbirds themselves have evolved together in this symbiotic relationship.  The hummingbirds get the nectar and the flowers reproduce by the transfer of pollen from flower to flower.

As more and more people are hanging up hummingbird feeders, more and more hummingbirds are frequenting them.  It is even enabling some hummingbirds to survive winters in climates formerly only frequented in the summer by migrating birds. 

Hummingbirds are sugar powered hunters.  All of their protein, fats and necessary vitamins and minerals come from insects.  They are very nutritious!  There would probably be no starvation in the world if humans would get over their aversion to eating insects. 

Ornithologists estimate that 60-80% of their diet is spiders.  They snatch many insects and spiders out of webs without getting tangled themselves.  They catch flying insects in mid-air.  Their incredible eyesight, speed and agility allows them to capture flying insects such as gnats, flies and mosquitos.