Accounting for the Skies

Every autumn, the Solothurn Jura becomes an extravagant staging ground for feathered trans-European commuters. High above Welschenrohr, at the Subigerberg observation post, volunteers spend their days tracking birds making their way toward the Mediterranean. It is a quintessentially Swiss exercise: high-altitude diligence, strict permit compliance, and a comfortable chalet from which to observe the wider continent's ecological shifts.

For almost six decades, observers associated with BirdLife have maintained vigil from dawn until dusk. Armed with binoculars, fine-mesh nets, and digital entry forms, they record every wingbeat passing through this designated nature reserve. The regime is thorough. Captured birds—ranging from chaffinches and blackcaps to marsh tits—are untangled, weighed, measured, tagged, and released. The trapping of wild birds is strictly illegal in Switzerland without explicit state authorization, making the station’s permit a coveted exception for scientific bookkeeping.

This year's autumn campaign follows a scorching summer across Europe, raising questions about how migratory species fared. On Subigerberg, the immediate picture appears deceptively tranquil. The local food supply resembles a lavish buffet, rich in berries and summer insects, leaving most trapped specimens noticeably plump with fat reserves. Yet, the broader reality contains quiet warning signs.

Barbara Schlup, who leads the station, points out that extreme heat leaves distinct scars. Swifts, for instance, suffered in overheated nest boxes during peak summer temperatures, with nestlings dying before they could fledge. Elsewhere, prolonged dryness baked the soil, forcing earthworms deeper into damp subterranean layers and out of reach for ground-foraging birds. Because the migratory population traversing the Jura originates from across Northern and Eastern Europe, local abundance at a single Swiss stopover can mask harsher conditions upstream.

The meticulous gathering of data on individual birds provides vital health checks, but single captures represent merely a fraction of a per mille of the total flyway population. An individual young robin, caught twice in two weeks before embarking on its maiden Mediterranean journey, tells a charming story, yet macro-level conclusions demand long-term rigor. The station’s real value lies in six decades of visual counting, which reveals shifting departure dates, fluctuating population counts, and the arrival of entirely new species.

Whether this summer’s heatwave marks a permanent turning point or a temporary spike remains a matter for statistical processing. The compiled data from 60 years of Jura monitoring is currently undergoing formal evaluation, with results expected before the end of the year. Until then, the volunteers will continue netting, measuring, and releasing, ensuring that every treecreeper and blackbird is meticulously accounted for before it leaves neutral Swiss airspace.

Written by Freya Stensrud freya.stensrud@alpineweekly.com