Slow paced and deploying minimal sound – apart from gentle bursts of voiceover and the sound of wings and planes taking off – this Swiss-set quasi-documentary about a bird sanctuary is relaxing to watch, like one of those machines that plays the sound of waves breaking to help you fall asleep. And like one of those sleep machines, it’s a rarefied piece of kit that only a specific set of customers will see the point of spending money on. But those select few will probably be entranced by its peculiar nature: it is not quite a work of fiction and not quite a doc, but one in which the non-professional cast mostly play versions of themselves.

At this secluded, exclusive Swiss sanatorium for injured avian creatures and distressed humans, the staff seem to be made up of people like protagonist-narrator Antonin (Antonin Ivanidze), who is recovering from cancer. Slender and blank of expression, like almost everyone else we see, and also apparently possessing only one set of clothes, like all the others, Antonin is shown how to raise rats and mice to feed the birds of prey by retiring employee Paul (Paul Sauteur). Also observed are veterinarian Emile Brethaut and keeper Sandrine Bierna, who also tend to the creatures, work that sometimes involves operating on them in vivid closeup – squeamish viewers beware.

Antonin mutters darkly about something being terribly wrong with the birds outside the sanctuary, inexplicable illnesses that afflict them, which leads some to come fluttering back, hoping to swap freedom for safety. Meanwhile, an owl who seems to have lost vision in one eye appears to have given up all hope and won’t hunt for itself any more. That low-level melancholy ratchets up in a climactic scene at an airport where Antonin suddenly collapses; but the reason why is as enigmatic as what was behind the decision to use an almost square aspect ratio with rounded corners that recall the images seen through an old View-Master.

• Bird Island is available on Mubi from 24 September.