Like other birds hummingbirds are warm-blooded, but so independently are the hawk-moths, which like a number of insects have evolved thermoregulation.

Quite often people say they have seen a hummingbird in Europe, which is most unlikely because these birds are confined to the Neotropical regions. What they have seen is a ‘hummingbirdoid’ (hummingbird-like) hawk-moth, also known as sphinx-moths. Hawk-moths are strikingly convergent on hummingbirds, both hovering motionless with proboscis/bill sucking up nectar from a flower. Indeed, even experienced naturalists can be deceived – Henry Bates, exploring and collecting in the Amazon, several times shot a hawk-moth, mistaking it for a hummingbird. Not only that, but the local people insisted that the moth could transmute into bird.

The convergence is striking in many respects: Not only does it include general body shape and hovering in a precise spot, but it also extends to metabolic, physiological and energetic convergences. Both have effectively arrived at an identical solution. Like other birds hummingbirds are warm-blooded, but so independently are the hawk-moths, which like a number of insects have evolved thermoregulation – in both cases elevated body temperatures are essential for the intense levels of metabolic activity.

Hummingbirds are today confined to the Neotropics, but interestingly their origins are apparently in the Old World and the oldest known fossils are from the early Oligocene of Europe. It has been speculated that a number of Old World plants have flower shapes eminently suitable for hummingbirds and may be relicts of a now vanished group. Hummingbirds are monophyletic, but there are some convergences with other birds, including swifts, reflecting the transition from an originally arboreal habitat to aerial foraging.

While nectar-feeding is strikingly convergent between hummingbirds and hawk-moths, it has also evolved independently in a number of other groups of birds, such as the sunbirds of Africa, Australo-Pacific honeyeaters and Central and South American flowerpiercers (Diglossa and Diglossopis, that “rob” the plant of its nectar by piercing the base of the flower and in doing so avoid acting as pollination vectors). Nectar-feeding is opportunistic in many other bird groups (e.g. the flowerpeckers of tropical Southern Asia and Australasia), and it has also evolved in the bats. A generally remarked difference is that only hummingbirds can hover, while all the others perch. Whilst broadly true, it is not a water-tight distinction. Hovering is seen in other nectar-feeders, especially sunbirds (and, of course, many hunting birds such as kestrels), but in these cases the bird cannot keep as precise a position as that achieved by hummingbirds in flight. Conversely, hummingbirds may perch to feed at times and sunbirds and honeyeaters often do so. Long tarsal bones and strong feet are shared adaptations in all such birds for effectively reaching flowers when perched, and all possess grooved or tubular brush-tipped tongues that generate capillary action for sucking up nectar from deep within the floral corolla.

Although other nectar-feeding birds do not share the precise hovering flight of hummingbirds and hawk-moths, some interesting metabolic convergences associated with the demands of a sugar-rich nectar diet exist, notably dealing with a lack of nitrogen (essential for proteins) and high water content of the nectar. Hummingbirds, sunbirds and honeyeaters all augment their sugar-rich diet with essential protein by sporadically eating small arthropods, such as insects and spiders.