Common swifts: the story of a trip without landing

If, when looking at the sky, you see a flock of birds resembling heavy metal swallows, fully dressed in black and larger than usual, you are watching common swifts (Apus apus). Like music bands, they like to show their high pitches so that everyone can hear them down here.

The format does not deceive—when there are “black scythes” in the sky, this means swifts are hunting. The flocks, often composed of dozens of individuals, are so noisy that they hardly go unnoticed. Its signature chant – a high-pitched, shrill chirp – is easily recognised on warm afternoons, echoing between quick aerial stunts.

This summer species can be seen all over the Portuguese territory between March and October. Some birds will only be in transit to other places, such as the Northern European countries, but others stay here during the warmer months.

Colonies form, often in urban settings, taking advantage of crevices in buildings and old structures to nest. Originally, these birds used cliffs and natural cavities, but the proximity of cities brought them new opportunities for shelter.

A life among the clouds

The common swift is about 16 to 17 centimetres long and, with a wingspan that can exceed 40 centimetres, is a true master of flight. It spends practically its entire life in the air: it feeds, drinks, sleeps and even mates in mid-flight.

Its body was shaped for this lifestyle: long, narrow wings, a slightly forked tail, and legs and paws so small that it is almost unable to land on the ground. The  name of its genus literally means “without feet,” Apodiform.  The English term swift, which designates the Apus genus, refers to its air speed and agility.

Their diet consists mainly of small insects and arachnids caught in mid-flight, an essential resource for controlling populations of mosquitoes, flies, and other pests. A single flock can consume thousands of these invertebrates per day, thus playing a major role in pest control in urban and rural ecosystems.

Mindful of the relevance of these birds and the impact of their presence on biodiversity, SPEA launched the National Network of Bird Sanctuaries. This project aims to halt the decline of several species, including swifts, by turning private properties into true wildlife refuges and promoting collective action for conservation.

Secrets of a group life

Common swifts are extremely social. They nest, migrate and feed in large groups, establishing contact through varied vocalisations and body language. They can fly more than 80 km from the nesting site to forage for food, adapting their flight height to weather conditions.

The breeding season occurs between May and July. The female lays two to three eggs, which are incubated for three weeks. Juveniles remain in the nest until they are ready to fly, which can take between 27 and 45 days. During this period, parents feed the chicks with insect balls held together with saliva, adapting the feeding as the young grow.

Thanks to their aerial ability and choice of nesting sites on vertical surfaces, they avoid most natural predators, such as the peregrine falcon (Falco peregrinus), the Eurasian Sparrowhawk (Accipiternisus) or the common buzzard (Buteo buteo). Their discreet colouring also aids camouflage, making them nearly invisible when not in flight.

Heading into the African winter

With the arrival of autumn, the swifts begin their long migration towards sub-Saharan Africa, from Zaire and Tanzania to Zimbabwe and Mozambique, where they spend the winter. The exact route is not yet fully known, but it is known that they can travel tens of thousands of kilometres per year, remaining almost permanently in the air.

Thus, from spring to summer, when the Portuguese sky is filled with black acrobatics and metallic screams, it is a sign that the common swifts are back. Invisible on dry land, they are a striking presence in the air. Tireless travellers who remind us how the natural world is also a moving symphony.

Did you know that…

• The scientific name of the common swift, Apus apus, refers to its appearance similar to that of swallows and its very short legs, which give the impression that the bird “has no feet”, deriving from the Greek term apous, which literally means “without foot”.
• The common swift is one of the few birds capable of entering a kind of dormancy during flight. This state of deep rest allows them to turn off half of your brain and reduce your metabolism to conserve energy during the long periods they spend in the air. Recent studies indicate that this ability is crucial for their survival during migrations and periods of food scarcity.
• During their impressive migrations, common swifts spend 24 hours a day in flight for about 10 months.
• The adaptation of common swifts to the human and urban environment has been beneficial for the species, providing them with safe places for reproduction.