I thought I might share some thoughts, and a case study as an example, on the importance of viewing commercially available hummingbird "nectars" as supplemental food only.
There are several foods on the shelves to attract hummingbirds to people's feeders. Most advertise that they contain vitamins and minerals that hummingbirds need, all of which may be true. Most are also much more expensive than plain old table sugar in water, and are capitalizing on the human compulsion to "do good" and spare no expense. A new wrinkle on this was just presented to me (a rehabilitator), with a 20 day old Black-chinned Hummingbird. It is called "Natural Springs Nectar" Hummingbird Food and it is sold in 58 oz bottles. It says "As advertised in Audubon magazine" on the label, implying (I think) an endorsement. The way to prepare this "food" is to add 3-4 cups of sugar, shake well and use within 90 days. In addition to various minerals and preservatives the material is said to contain vitamin A, C, D-3 and E. All this may be good stuff (though the continued presence of vitamin C for 90 days would be debatable) but it is not adequate hummingbird food. In addition, though the vitamin to enable the metabolism of calcium and good bone development is included (D-3) there is no mention of calcium or phosphorus on the label.
The case study is the bird that arrived with the bottle of food. Its age, as determined by bill length, was 20 days. The people who found the bird on the ground had been feeding it for 10 days. So, it must have been 10 days old when it was found. At this stage the bird would not have reached its full weight (though it should be about 3 grams), its parent would no longer be brooding at night and the bird would have pinfeathers. Ordinarily it would continue to be fed insects until day 21 when it would fledge and start experimenting on its own. In this case it had been fed the "food" described above.
The bird was brought to us because "it used to fly and now it doesn't." Its weight two days after arrival an stabilization was 2.4 grams and it sits in an uncharacteristic horizontal position, not yet flying. I suspect borderline rickets (metabolic bone disease) as well as general malnutrition. It is responding to treatment.
In short I'm increasingly concerned about the plethora of "empty" calories in the guise of food appearing on the shelves for these birds. While I don't suggest a problem in using it for adults I urge people to discourage thinking of it as "food" but rather as an attractant to bring them into human view. People who find "babies" need to get them to people who can offer real food before lasting harm is done.