The Common Swift: A Master of the Skies Nesting in the Walls of the Faculty of Science
On June 7, renowned ethologist Jane Goodall endorsed “World Swift Day,” a global event dedicated to celebrating swifts. The common swift (Apus apus) is a bird that anyone can spot performing high-speed aerial acrobatics around the buildings of the Faculty of Science during spring and summer.
A Life in the Air
This species is a remarkable example of adaptation to aerial life: a streamlined body, extremely long, narrow, sickle-shaped wings with stiff feathers, and a flat head aligned with the body. Their cruising speed is around 50 km/h, but swifts can easily exceed 100 km/h in a dive.
Common swifts spend the vast majority of their lives in the air.
Telemetry studies have shown that some individuals can remain in continuous flight for ten months without ever landing. They only need to return to solid ground to lay eggs and raise their chicks. Much like penguins—adapted to aquatic life—swifts are clumsy on land. Their atrophied legs make walking extremely difficult. They cannot perch on branches or wires but can cling to vertical surfaces. If they fall to the ground, they are unable to take off again, hindered by their long wings and tiny legs.
Feeding, mating, preening—all take place in flight. Since sleep is a vital physiological need, it is believed that swifts also sleep while flying, using unihemispheric sleep, a common trait among birds. One hemisphere of the brain rests while the other remains alert. Miniature accelerometers placed on the backs of swifts have revealed extended periods of gliding at high altitudes, interpreted as sleep phases.
Insects, Migration, and Meteorology
Their movements are dictated by the availability of their prey—flying insects caught mid-air. Swifts come to breed in Switzerland during the peak of flying insect abundance, from late April to August. Due to their aerial lifestyle, there is little data from bird band recoveries to track their movements. However, advances in geolocation tag technology and miniaturization have made it possible to equip and track these birds, despite their tiny weight of just 50 grams. They travel thousands of kilometers to reach sub-Saharan Africa, particularly in West and Central Africa—from Ghana to the Democratic Republic of the Congo—flying over ecosystems rich in insects such as tropical forests and moist savannahs. When weather conditions are unfavorable for flight or insect activity, swifts may travel hundreds of kilometers over several days in search of better conditions. Swifts breeding in Switzerland may even move temporarily to the Mediterranean region while awaiting more favorable weather.
A Vulnerable Urban Colonizer
Urban biodiversity is relatively poor. The black swift’s original breeding habitat consists of rocky cliffs, but it has successfully adapted to urban environments by nesting in building crevices and spaces beneath rooftops. Cliff nesting is now very rare. Finding a suitable cavity or nest box can take several years. Young swifts do not breed until they are 3 or 4 years old. Once a pair forms, they often remain faithful over the years and return to the same cavity to lay eggs.
The main threat currently facing this species is the renovation of old buildings, which often involves sealing all cracks and cavities, as well as new constructions with exterior insulation. The black swift is protected under the Swiss Federal Law of June 20, 1986, and holds special status in the Canton of Geneva through Cantonal Motion M2198. Integrating nesting sites into renovation or new construction projects for tall buildings is a key compensatory measure to help sustain the species.
The Faculty of Science on the Front Line
Black swifts have been nesting for several years in the façades of the Faculty of Science, particularly on the fourth floor of the Sciences 3 building. However, their presence remains precarious due to the operation of window blinds or during cleaning or renovation work on the façades. For instance, when blinds are lowered, nests become inaccessible via direct flight. With nearly 200 nesting cavities on the Sciences 3 building, the Faculty of Science holds direct responsibility for the preservation of this protected species. In April 2025, around forty nest boxes were installed on the Sciences 3 façade with the expertise of the Genthod Ornithological Rehabilitation Centre. In 2026, the installation of an additional 120 nest boxes is planned. This will be complemented by heightened vigilance to limit construction or cleaning work between April and August.
The black swift symbolizes the delicate coexistence with urban biodiversity. Its preservation depends on coordinated efforts and concrete actions—such as those undertaken by the Faculty of Science—to maintain suitable habitats.
Swiss stakeholders in swift conservation:
References
- Åkesson S. et al. 2012. Migration routes and strategies in a highly aerial migrant, the common swift Apus apus, revealed by light-level geolocators. PLoS One 7(7). DOI: 10.1371/journal.pone.0041195
- Hedenström U. et al. 2016. Annual 10-Month Aerial Life Phase in the Common Swift Apus apus. Current Biology 26(2). DOI: 10.1016/j.cub.2016.09.014
Dr. Michel Gauthier-Clerc, Scienscope Director
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