The Dutch national bird, the black-tailed godwit, spends more than 20% of its migration flying time at very high altitudes en route to its West African wintering grounds. Altitudes of at least five kilometres and sometimes nearly six are not unknown. This has been revealed by new research, published this week in the Royal Society Journal Proceedings B, by Dr Nathan Senner of the University of Groningen / University of Montana and his team. The results are amazing because godwits are true lowland birds. They should lack the physiological adaptations needed to fly at altitudes where the partial pressure of oxygen is less than 50% of that at sea level, particularly to the red blood cells. Only the geese that migrate over the Himalayas ought to be able to do this.
In this remarkable study, postdoc researcher Nathan Senner and colleagues from the UG and the University of Amsterdam
used GPS trackers to measure the flying altitudes and wing beat frequency of migrating godwits. The data were combined with information about wind, temperature and air pressure. In addition to the noticeably long periods of time that godwits fly at high altitudes, the fact that they do this despite there being no topographical barriers to cross stands out. The very high flying altitudes may be related to avoidance of high air temperatures at lower levels. Godwits also benefited from more tailwinds at higher altitudes.
Nathan Senner: ‘Nearly 20% of all birds annually migrate long distances between their breeding grounds and their wintering grounds. These treks require legendary “sport performances” – performances that turn our ideas about the limits to endurance and physiology upside down. Take the treks by bar-tailed godwits across the Pacific Ocean, 11,000-12,000 kilometres non-stop from Alaska to New Zealand. And what about the treks by geese over the Himalayas. Our own godwits had even more surprises in store for us, though!’
Thanks to these results, migratory bird biologists have had to revise their general ideas about the frequency of high altitude flying. Lowland birds have a greater capacity to fly high than they considered even possible. Flights at high and extremely high altitudes are probably a lot less unusual than we’ve always thought.
EU ITN granted to MANIC
Prof. Maria Antonietta Loi of the Zernike Institute for Advanced Materials (ZIAM) has been awarded a Materials NL Changes grant by the NWO.
Dr. Francesco Maresca has been granted a Materials NL Challenges grant by NWO.