High-speed video has revealed for the first time how male Common Snipes Gallinago gallinago generate their distinctive drumming display flight. ‘The exciting thing was that the video revealed that the tail feather actually flaps backwards and forwards, like a flag blowing in the wind,’ said Dr Roland Ennos, from the University of Manchester’s Faculty of Life Sciences.
Dr Ennos added: ‘Most tail feathers are rigid, so would be stiff in the wind in order to provide aerodynamic lift.’ But the outer tail feathers of the male Snipe actually cause drag and so slow the birds down. ‘Therefore, by going fast and making a lot of noise, the bird is showing prospective mates how fit it is,’ Dr Ennos said.
During courtship flights, the male climbs to an altitude of c. 50 m before diving at about 40º with the outer tail feathers extended. The researchers found that when the birds reached a speed of 50 kph (31 mph) the outer feathers produced an audible sound. The feathers continued to produce the sound until the bird reached speeds of more than 86 kph (53 mph).
The team reported that the drumming was created by an ‘aeroelastic flutter’, a potentially destructive vibration. It was aeroelastic flutter that caused the Tacoma Narrows suspension bridge in the USA to wobble and collapse in November 1940, just a few months after it opened. ‘In order to measure the frequency of sound that the feather made, we simply stuck a feather in a wind tunnel,’ said Dr Ennos. ‘But to capture the video footage was more tricky. So we put the feather in front of a hair dryer and filmed it when it was fluttering.’
He said that the findings could be used to shed light on how different species of snipe produce different-pitched calls. ‘Snipe species with narrower tail feathers have higher-pitched calls. Our findings could help to explain this.’ Interestingly, a displaying North American Wilson’s Snipe G. delicata was discovered by Finnish birders displaying in central Finland near the city of JyvÃ¤skylÃ¤ in mid April. This is the first record of a Wilson’s Snipe to be seen and heard displaying in Europe and, indeed, it may have been present in spring 2008 and 2009, too. If so, it overlapped in Finnish airspace with another extralimital snipe – a Swinhoe’s Snipe G. megala from east Asia in 2008. The distinctive sound of their drumming display flights is what first alerted birders to their presence.