Hummingbirds

Hummingbirds, which belong to the Trochilidae family, are the smallest birds in the world and are exclusive to the American continent, and comprise more than 300 species concentrated in tropical and equatorial areas although some of them are present in temperate and even cold regions such as southern Alaska or the Tierra del Fuego. The average weight of these tiny birds ranges from 3.5 to 9 grams. Their diet is generally and mainly nectarivorous (nectar constitutes up to 90% of their diet), supplemented by insects. They can take in an amount of nectar equivalent to their body mass in less than a day.

The different shapes and lengths of their beaks are the result of a species-specific adaptation to the different shapes of the corollas of the flowers they visit, which creates a close relationship between the hummingbird and the plant. In sucking the nectar, the hummingbird's beak and head remain soaked in the pollen of the flowers, and when it moves from one flower to another, it plays the role of pollinator, as do bees, butterflies and many other animals. This represents a typical example of coevolution with mutual benefit for both species (dispersive mutualism).

The legs are very short and do not allow walking, but they are excellent fliers. In fact, another well-known characteristic of hummingbirds is their ability to hover, and, unique among birds, to fly backwards, or even upside down, thanks also to the high frequency of their wing beat which can vary, depending on the to the size of the species, from 10 to 80 strokes per second. Despite their small size, they take very long flights (some hummingbirds need to increase their body weight by 50% before migrating) to follow seasonal blooms, and some species even migrate for several thousand kilometers.

Due to their small size and the energy costs of their flight, they are characterized by a very high metabolism. For this reason, between meals and during sleep they fall into a stupor that allows them to save energy resources by significantly lowering their body temperature.

There are two subfamilies of hummingbirds: Phaethornithinae, which generally have brownish, greyish, and reddish colors and no iridescence, and Trochilinae, which often have iridescent feathers that are metallic red, orange, green, and blue. The brilliant colors of the plumage derive from horny lamellae interposed between the feathers, which act as optical prisms breaking down the light into the various colors. Iridescence occurs most in males and is mainly prevalent on the head and neck. Males of some species sport crests, plumes and various ornaments, such as in the chin strap, and elongated tail feathers. Males attract females through singing, iridescent plumage, and exhibition flights. They are very territorial and for this reason they become aggressive even with conspecifics. The females, always larger than the males, are less colorful and lay eggs the size of a coffee bean.