Sunbirds and hummingbirds may look similar at first glance, but they are actually quite different birds that belong to separate taxonomic families. Both types of birds have evolved to feed on nectar, leading to some convergent adaptations such as long bills and the ability to hover. However, sunbirds and hummingbirds have distinct evolutionary histories and are not closely related.
Taxonomy
Sunbirds belong to the family Nectariniidae, which is part of the larger passerine order Passeriformes. There are over 130 recognized species of sunbirds found throughout Africa, southern Asia, and Australia. They are sometimes also called spiderhunters.
Hummingbirds belong to the family Trochilidae, which is part of the order Apodiformes. There are over 330 recognized species of hummingbirds found only in the Americas. This is a much more restricted geographic range compared to sunbirds.
Sunbirds and hummingbirds are in completely separate taxonomic orders, which indicates they are not closely related at all. Orders are a high level division in taxonomy, so belonging to different orders means the two groups separated evolutionarily over 50 million years ago.
Anatomy and Physiology
Sunbirds and hummingbirds share some anatomical and physiological adaptations related to feeding on flower nectar, but they have many distinct differences as well:
- Bill shape: Sunbirds have long, thin, downcurved bills. Hummingbirds have shorter straight bills.
- Tongues: Sunbirds have broad brush-tipped tongues. Hummingbirds have forked fringed tongues that allow them to lap up nectar.
- Wings: Sunbirds can hover but have more limited flight abilities compared to hummingbirds, which are specialized for sustained hovering in place.
- Legs: Sunbirds have thicker legs for perching. Hummingbirds have very short legs used primarily for perching briefly.
- Metabolism: Hummingbirds have an exceptionally high metabolism to power their unique flight abilities. Sunbirds do not.
Overall, sunbirds and hummingbirds have adapted to nectar-feeding in different ways based on their distinct evolutionary histories. Their anatomical differences reflect their lack of close relationship.
Reproduction
Sunbirds and hummingbirds also show major differences in their reproductive biology:
- Courtship: Sunbirds do not engage in courtship displays. Male hummingbirds perform elaborate courtship displays.
- Nests: Sunbirds build covered nests out of vegetation, spiderwebs, and other materials. Hummingbirds build small compact cup-shaped nests out of plant down and spider silk.
- Clutch: Sunbirds lay 1-4 eggs per clutch. Hummingbirds lay only 2 eggs per clutch.
- Incubation: In sunbirds, only the female incubates the eggs. In hummingbirds, incubation duties are shared by both sexes.
- Care: Sunbird chicks are altricial at hatching. Hummingbird chicks are precocial and able to thermoregulate soon after hatching.
These very different reproductive strategies again point to sunbirds and hummingbirds being evolutionarily distant lineages without a close relationship.
Geographic Range
The geographic distributions of sunbirds and hummingbirds provide further evidence that they are not closely related:
- Sunbirds are found exclusively in the Old World – Africa, southern Asia, and Australia.
- Hummingbirds are found only in the New World – the Americas.
- There is no overlap in their ranges. They do not co-occur anywhere naturally.
The fact that sunbirds and hummingbirds live on completely separate continents supports that they have independent evolutionary histories going back tens of millions of years to when the supercontinent Gondwana fragmented.
Fossil Record
The fossil record provides final confirmation that sunbirds and hummingbirds are evolutionarily distant:
- Oldest sunbird fossils date to around 23 million years ago in Europe.
- Oldest hummingbird fossils date to around 30 million years ago in Europe.
- There are no transitional fossils showing a direct link between the two groups.
The fossil evidence indicates sunbirds and hummingbirds started separating well over 50 million years ago and their lineages do not seem to intersect at any point.
Conclusion
While sunbirds and hummingbirds feed on nectar and can hover, they are not closely related. They belong to different taxonomic orders, have major anatomical and reproductive differences, live on different continents, and have distinct fossil records going back over 50 million years. Convergent evolution to fill similar niches has led to some species in these groups independently evolving similar traits associated with nectar-feeding. However, the totality of evidence indicates sunbirds and hummingbirds are evolutionarily distinct lineages that separated tens of millions of years ago.
