To avoid colliding with obstacles, natural and otherwise, cranes alter their behavior when they have to fly through thick, obscuring fog. Rather than head in a straight line towards marshy areas where they forage for food, they linger longer around the roost and eventually fly around in circles, according to a new study published in The Wilson Journal of Ornithology.
How birds behave in very low visibility conditions remains poorly understood. A team led by Eileen Kirsch of the U.S. Geological Survey had the unique opportunity to observe tall, elegant sandhill cranes (Grus canadensis) flying in heavy fog during a two-year study at the Horicon Marsh of southeastern Wisconsin. The researchers recorded the birds’ flight patterns with a portable marine radar at various locations throughout the day and visually counted cranes when they left their roosts in the morning. Then, the team compared flight patterns during foggy times with that of clear skies. When visibility was good, the cranes tended to depart from their night roost shortly after sunrise, flying in straight paths toward their foraging areas.
In the fog, however, the cranes left their roost later in the day, didn’t venture far, and engaged in a circling flight before returning to the roost instead of heading towards their foraging areas. “They were going every which direction, which we’ve never seen before,” Kirsch told New Scientist. It's likely they were reluctant to fly farther than they could see and wanted to keep the flock together. While these larger birds can afford to not forage for a bit, hunger eventually drives them to flight, despite the poor visibility. “It was very cold, and energetically they needed to eat,” Kirsch added.
Furthermore, compared to clear mornings, cranes flying in the fog called more frequently. In fact, during the study period, the team only heard the young of the year call out during the fog event.