Despite being quite common in the UK, swifts like to lead a kind of colony life and come back to the same areas they have always inhabited, often towns with old buildings and with water nearby. New houses don’t have the eaves and holes that they prefer, and even putting up a swift box won’t attract them unless there are already swifts nesting nearby. Both Hitchin and Arlesey have their share of nesting swifts, but I had only ever spotted the odd one flying over Fairfield until last year, sitting at the outdoor cafe at Bannatynes, when my wife and I saw about a dozen of them flying in circles overhead and screeching. We supposed they must have had nests in the western end of Fairfield Hall. Have any residents noticed them this year?

Often said to be the harbinger of summer, the common swift is a migratory bird, spending winters in Africa and summers in almost every country in Europe, including as far north as Finland. The distance it has to travel means that it is one of the latest migrants to arrive – seldom seen in the UK before the end of April and gone before the middle of August.

Common swifts are 15–17cm long with a wingspan of 38–40cm. They are entirely blackish-brown in colour except for a small grey patch on their chins. They have a short, forked tail and swept back wings that look like a boomerang in flight. Their call is a loud scream with the higher pitch being the female. They often form screaming parties during summer evenings when up to thirty swifts gather in flight around their nesting areas. The reason for these performances is unclear, but might be associated with the ascent to higher altitudes, because swifts sleep ‘on the wing’, by catnapping, except for the breeding adults who spend the night in the nest.

Swifts mature and breed when they are four years old. Those that survive their juvenile years can expect to live a further four to six years – and some ringed birds have been recorded up to 20 years of age. Pair bonds are often formed when the birds are just a year old and young birds sometimes occupy a nest hole and even attempt to build a nest once they have paired, but they are unlikely to breed successfully until they are four years old. They pair for life, meeting up each spring at the same nest site.

A swift’s nest is located high up in the roof space under the eaves of old houses or churches with enough height for the bird to be able to drop into the air from the nest entrance. Swifts cannot land on the ground – their small legs and feet are only designed for clinging onto vertical surfaces, so you won’t see them congregating on telephone wires as they prepare to return to Africa. The saucer-like nest is built by both adults from any material that can be gathered on the wing. It includes feathers, straw, paper and seeds, all cemented together with saliva. The nest is renovated and reused year after year.

Swifts lay two to three cream coloured eggs, slightly elongated to avoid rolling in the nest, at two to three day intervals and incubation starts as soon as the first egg is laid and lasts for 19 to 20 days for each egg. The adults share all the nesting duties equally. The young hatch a couple of days apart so that, unusually for small birds, the young are different sizes. The young grow rapidly on a diet of insects and at two weeks old start to exercise by doing press-ups on their wing tips. They are ready to fly at about 6 weeks old. They usually leave the nest in the early morning and are independent immediately. Within a few days they will start their flight to Africa with other groups of fledglings. They will feed and sleep on the wing until they are ready to nest themselves.

Peter Land