Hummingbirds are very interesting and unique birds for more reasons than might be readily apparent. In addition to possessing the ability to hover, they also have some unique anatomical features; have co-evolved alongside the flowering plants from which they derive energy, and have developed methods to conserve that energy; and are one of the only groups of birds that have a truly promiscuous mating strategy.

Hovering is accomplished when hummingbirds beat their wings horizontally in a figure 8 pattern while varying the angle of their wings in order to balance the force they generate, thus allowing them to stay perfectly stationary. To do this, they have a stronger supracoracoideus (the muscle that raises the wings; the pectoralis muscles lower them) than is typical for most other bird species, and are also capable of rotating their wings to a much greater degree than other birds. In addition to hovering, this allows them to fly backwards and upside down; something that no other bird is capable of. In typical flight, their wings move up, forward, down and then back — just like other birds. It is visually equivalent to the butterfly stroke that human swimmers use.

Hummingbirds feed by inserting their bill into a feeder or a flower, and use their tongue (which is bifurcated) to scoop up nectar. In the process of doing this they also collect pollen that is then transferred between different flowers and plants. This mutually beneficial relationship has resulted in hummingbirds seeking out very specific types of plants that possess long tubular flowers without landing platforms. Because there are vastly fewer hummingbird-pollinated plant species than there are insect-pollinated species, such plants do not have to produce a lot of pollen since the chance that the hummingbird won't visit another member of its species, or a different flower on the same plant, is very small. The energy that the plant saves by producing less pollen can then be invested in enriching its nectar's sugar content to attract hummingbirds in the first place. Hummingbirds also consume small insects for the protein content that they offer, as protein is required by all birds to produce feathers.

Hovering requires an extremely rapid metabolism, and the energy costs incurred by hummingbirds to fuel that metabolism is huge. In fact, if it weren't for one very important strategy they would starve to death between going to sleep at night and waking up in the morning. This strategy is called torpor, and other animals besides hummingbirds also utilize it. Torpor is a physiological process by which metabolism and bodily functions (respiration, digestion, heart rate, etc.) are dramatically reduced to the point that it takes upwards of 15 minutes for a hummingbird to fly upon exiting the state.

Metabolism isn't the only thing that's fast about hummingbirds. Unlike the overwhelming majority (90%) of all bird species, hummingbirds are not monogamous, but promiscuous. Males establish a territory with as abundant a supply of food as they can find and successfully defend from other males, and display for any female that comes to feed. Males do not have any interaction with females beyond courtship and mating, and as such do not help take care of any offspring that result from their liaisons.

Now you know not to get your significant other that hummingbird promise ring.