Swifts aren’t quite what they seem
Swifts are the UK’S archetypal summer birds, arriving as late as mid-may and gone again in early August. Their screaming flights through city streets and above suburban gardens are certainly a memorable part of the warmer months. It’s hard not to feel slightly short-changed, though, when you realise who the closest relatives of their order (Apodidae) are. As well as the treeswifts (Hemiprocnidae) of southern and eastern Asia, they are joined in the order Apodiformes by the hummingbirds, of the New World. The two lines of the family (insect-eating swifts and treeswifts, and nectarguzzling hummingbirds) diverged as long as 42 million years ago, with the hummingbirds then further diversifying into 338 species in response to the myriad habitats of the Americas, and the many different plant species therein. There is an Old World family of birds that, at first sight, might seem to be closely related to hummingbirds – the sunbirds of Africa and Asia (although they generally perch to feed, rather than hover). In fact, though, this is an example of convergent evolution, in which families of only distantly related birds evolve many of the same characteristics in order to fill the same ecological niche. Another family, the honeyeaters of Australia, have similarly evolved separately but along similar lines.
CONVERGENT EVOLUTION Blue-faced Honeyeaters fill a similar niche to sunbirds and hummingbirds DIVERSE DEVELOPMENT A Marvelous Spatuletail – there are more than 300 different hummingbird species UNIQUE Sword-billed Hummingbirds have evolved amazing bills to allow them to feed deep inside flowers