On fine summer evenings Swifts gather in “low flying screaming parties” as birds chase each other excitedly around the buildings where there are nests in high speed, aerobatic groups. This is often the only evidence of breeding as Swifts make no mess and return to their nests very quickly and discreetly.
Because they rely on insect food, Swifts can only live in the UK for a short period each year, when the weather is at its best and when the days are at their longest. Swifts migrate south to Africa in early August once they have finished breeding, returning only at the beginning of May.
Swifts are a bird in trouble. They need gaps and holes in buildings to nest and so when changes are made to buildings they often lose their nest sites. These can include new soffits, re-roofing or roof insulation which block up the access holes they need. Modern houses are no longer providing nest sites for Swifts. As a result Swift numbers are declining rapidly.
Swifts feed on airborne insects and spiders which are only available in warm weather so swifts can only live in the UK for a short period each year. But where do they go once the breeding season is over?
Swifts leave as soon as they have finished breeding. Newly fledged swifts can fly immediately and undertake the long route south without the help of their parents. In Hampshire, swifts which are still too young to breed leave at the end of July whereas breeding birds and their young leave from the end of July into August, with most having departed by mid-August. If you see swifts later than that they will be migrating south from more northerly parts of the UK and Europe.
Recently the migration route of swifts has been successfully followed by researchers at the British Trust for Ornithology. The map shows the route taken by swift number A320.
As soon as A320 left on the 23rd July she flew to central Spain for a couple of days to refuel, then travelled all the way to West Africa in a single flight and spent a few days there. After that she covered huge distances, never landing, searching out good feeding areas across equatorial and southern Africa from August through to April. In April she started the return route with a mammoth 3 day flight across the Atlantic from Congo to Liberia followed by a 10 day period of feeding before crossing the Sahara desert and returning to breeding areas in Europe in time for good weather and a plentiful supply of insects.