Birds circle and stick together to help them fly in dense fog

FOG can ground birds – but not always. One November morning in the Horicon wildlife refuge in Wisconsin, heavy fog settled. A group of sandhill cranes still set off from their roost to reach foraging areas despite the fog, providing a rare opportunity to study how the birds fly when visibility is very low.

Eileen Kirsch of the US Geological Survey’s Upper Midwest Environmental Sciences Center in La Crosse and her team recorded the event and saw the cranes flying cautiously, staying close to the roost. The birds went in circles rather than straight lines. “They were going every which direction, which we’ve never seen before,” says Kirsch. She thinks they were reluctant to fly further than they could see and were also trying to keep the flock together (The Wilson Journal of Ornithology, doi.org/65g).

The cranes also called more frequently and loudly than normal. This is common among birds flying in low-visibility conditions, says Graham Martin at the University of Birmingham, UK. It probably allows them to stay in touch. Usually, though, when there is fog, mist or heavy rain, large birds such as cranes, duck and geese stay put until conditions improve. “They can afford not to venture to foraging grounds for a couple of days,” says Martin.