By Chris Jarvis, Education Officer
This week is Swift Awareness Week and that means it’s time to celebrate our screaming summer visitors – the avian ones, that is.
Here at the Museum we eagerly await the return of these long distance migrants each May. This is not only because for many of us they herald the start of summer, but also because the swifts that nest each year in the Museum tower are part of the longest-running continuous study of any bird species in the world.
Taking the long view of these amazing birds we know that, like all birds, they evolved from a particular group of dinosaurs. Birds, in effect, are living dinosaurs. The earliest fossil swift, the ‘Scania Swift’, is around 49 million years old and shows us that by this time they had already evolved in forms that are virtually indistinguishable from today’s birds. Today, they have diversified into around 100 different species including our Common Swift (Apus apus).
Swifts have taken life on the wing to the extreme. Not only are they the fastest recorded bird in level powered flight, reaching speeds of nearly 70mph, but once launching themselves from the nest that they hatched in they may not land for the next two years of their lives!
They are so adapted to life in the air that they are capable of eating, mating and even sleeping on the wing. During sleep, it is thought that the two hemispheres of the brain take it in turns to nap as the swift slowly circles at heights of up to 30,000 feet. They do not even land to collect nesting material, instead relying on whatever feathers or pieces of plant material are floating in the air to build their nests.
During this two-year flight they will follow their food – the seasonal blooms of flying insects that appear after summer rains – on a 14,000 mile annual migration to southern Africa and back, living in perpetual summer.
Whilst for a long time scientists thought swifts were closely related to similar looking birds, swallows and martins, DNA analysis has revealed that they are the product of another amazing type of evolution – called convergent evolution – where organisms with similar lifestyles independently evolve similar traits. It turns out that whilst swifts may look like swallows, they are actually more closely related to hummingbirds; swallows, on the other hand, are more closely related to kingfishers than to swifts.
Studies show that the population of breeding swifts in the UK has roughly halved between 1995 and 2016. The causes of this decline are debated: Lack of nest sites, lack of food, and changes to global weather patterns have all been implicated. The truth is that a bird which lands only once a year is extremely difficult to study.
We hope for a successful breeding season here in the tower, but if you would like to observe them yourself you can watch the swifts on our nest cam and compare the ups and downs of their populations over the years on our website.