From nature documentaries such as the BBC’s Blue Planet, we know that some fish species swim in huge shimmering shoals to confuse or deter predators. Perhaps less well known, though, is that some birds such as dunlins do this too, in aerial displays called murmurations.
In the UK, the autumnal and winter displays by starlings are the most common as birds gather in vast flocks near dusk, wheeling and soaring almost as one for a few minutes, before dropping down onto the roost. This behaviour can be seen in many towns and cities.
However, some wading birds also exhibit this behaviour, notably the dunlin and the knot, commonly found feeding on mudflats in estuaries. On the ground, both are fairly nondescript and smaller than many garden birds, but in flight their long, elegant wings are on display, tapering gradually towards the ends to aid long distance migration.
With a pale underbelly and grey, black and white upper surfaces, their appearance changes from dark to light as they twist and turn, with some birds seeming to almost disappear when flying head on. In large flocks, this can lead to rapid changes in colour, with rippling patterns appearing, and even unusual strobing effects and oval patterns.
There are many theories about how such aerobatic feats are possible, but computer simulations have shown that this behaviour can be reproduced with just a few simple rules, in which each bird sets its flight path based on that of its closest neighbours. Also, although birds on the outside respond to threats such as birds of prey, there is no overall leader.
These displays are truly one of the wonders of the natural world and during autumn and winter can sometimes be seen in estuaries and at the coast. Some well-known viewing spots include the Ribble, Dee and Mersey estuaries in northwest England and the RSPB’s Snettisham reserve in East Anglia.
As with any natural phenomenon, good luck and timing is required, and some factors which help include unusually high tides, which force birds in close to the shoreline, and in estuaries the passage of a tidal bore. For photographers, for the most spectacular images, picking a location with the sun behind you helps, as does a telephoto lens; see here for more tips.
For more information on when and where to see murmurations, see RSPB and Wildlife Trust websites, but be sure to check tide tables and the tidal safety advice from the RNLI to avoid getting caught out by the tides. There are also some superb videos of murmurations online of which Dance of the Dunlins is one of the best.
If you are interested to read more about where to see dunlin murmurations around the Mersey Estuary and on the Wirral, my book The Mersey Estuary: A Travel Guide has more information. Click this link for details.