If you want to know what the weather is doing, look out for birds flying high. As folklore says, Swallow flying high, staying dry, / Swallow flying low, wet will blow.
Swallows earned their weather-forecasting reputation because they fly high to catch insects wafted up on thermals during fair weather, but when rain is approaching the insects and birds fly lower.
High-flying birds can now be enlisted as “weather stations”, sending back reports from remote places where measurements are limited. This venture is the result of abreakthrough in the development of lightweight GPS (Global Positioning System) transmitters that can be safely strapped on to the backs of birds. The devices show the bird’s location, speed and altitude. A bar-headed goose has been recorded flying at 7,315m (24,000ft) over the Himalayas, thought to be the highest bird migration in the world (Weather Eye, September 11).
Now a study has used trackers on griffon vultures, birds with wings spanning more than two metres (6ft). The transmitters revealed how the vultures often soared on thermals in search of food. They moved upwards so efficiently on sunny days that it was possible to calculate how fast a thermal of air rose based on the GPS information, something difficult to measure any other way. Because thermals move with the wind, the speed of the wind and its direction are calculated from the movements. Comparisons with measurements made from weather stations on the ground showed that the vultures provide accurate measurements.
Birds could even provide reports from remote areas. Hundreds of thousands of birds of prey migrate over the Sahara and Sahel, where there are fewer observations. These birds could provide valuable weather information that would help improve forecasting models. Future collaborations between biologists and meteorologists could enlist more birds to give an even larger-scale weather picture for forecasters.