Griffon vultures measure the weather
Data generated by GPS tracking devices used in the University of Amsterdam (UvA) Bird Tracking System (UvA-BiTS) to study bird behaviour have such a high level of accuracy that they can be used to deduce weather measurements. This was revealed in a study carried out by the UvA Institute for Biodiversity and Ecosystem Dynamics (IBED). The results of the study were published in the authoritative scientific journal Bulletin of the American Meteorological Society and as a research highlight in Nature.
Bird flight behaviour patterns are closely linked to the weather. Birds are reluctant to fly during rainy or stormy weather. The altitude at which they fly often depends on the wind and some large birds use thermal currents to gain height without having to flap their wings. Knowledge of the influence of the weather on bird behaviour is increasing and UvA-BiTS researchers are using tiny GPS backpacks (small GPS transmitters attached to a bird's back) to track exactly what birds are doing. By bringing together these insights and GPS data, measurements of the weather conditions can now be performed.
Efficient use of thermals
Working with meteorologists from Ohio State University and environmental scientists from the Universté de Montpellier, IBED’s Jelle Treep, Judy Shamoun-Baranes and Willem Bouten analysed the GPS data supplied by griffon vultures living in Les Grand Causses national park in Southern France. Wing-flapping consumes too much energy so when the sun shines griffon vultures frequently take advantage of thermals to gain altitude and proceed to soar in search of food or a new thermal column. They use this technique so efficiently that it is possible to estimate how fast air rises in a thermal column based on GPS data. This is extremely difficult to measure with other methods. Because thermal columns move with the wind, wind velocity and wind direction can simultaneously be ‘measured’ by way of the birds’ movements.
By comparing the estimates of wind velocity, wind direction and vertical movements of the air with measurements taken by weather stations on the ground and with detailed weather models, the researchers have shown that GPS data can be used to take weather measurements in locations where there is no or limited availability of regular weather sensors. One example is the hundreds of thousands of GPS points of migrating birds of prey over the Sahara and Sahel stored in the UvA-BiTS database: these results can be very useful in efforts to improve weather forecasting models.
The article is based on the results obtained from a study carried out by Treep for his Master's thesis at the University of Amsterdam. Treep is currently carrying out doctoral research at the Institute for Environmental Biology at Utrecht University on the influence of the wind and thermals on the dispersal of plant seeds.
H.J. Treep, G. Bohrer, J. Shamoun-Baranes, O. Duriez, R.P.M. Frasson, W. Bouten: ‘Using
high-resolution GPS tracking data of bird flight for meteorological observations’, in Bulletin of the American Meteorological Society (2015), in press. Doi: 10.1175/BAMS-D-14-00234.1