Bird migration is one of the miracles of this planet, and one of its great mysteries. We know why birds migrate - to improve chances for survival of the species through better food availability and breeding conditions - but are less sure how they do it. We know they build up strength and body fat, and navigate according to landscape, wind, thermals, sun, stars, moon, memory, magnetic fields, but many achievements, of individual birds and whole species alike, are mind-boggling in scale and complexity. This film by the producer of the insect saga Microcosmos favours boggling over exploring or explaining; regrettably, despite impressive camerawork, it doesn't even boggle that well. The problem lies not with the dire music, nor with the vague, portentous (if mercifully sporadic) voice-over, nor with the fact that some of what we see has little to do with migration (why are those macaws in there?). The main flaw is the film-makers' inability to tell a clear story. We first follow birds flying north from various places to the Arctic, then return to the Equator before an abridged rerun in the southern hemisphere. Inaccuracies and anthropomorphic distortion are rife - that picturesque penguin pair isn't really mourning a chick fallen prey to an albatross. And because the focus is so fixed on geese, swans, storks, cranes, geese and more geese, both the narrative and the images get a little tedious. Couldn't we at least have had a swallow, a warbler, or a bottleneck of massed raptors soaring over the Bosphorus or the Strait of Gibraltar? A wasted opportunity.