BIRD MIGRATION UNDER THE SPOTLIGHT

 

Pictured (from left): Phil Espin (LBC), Prof Ian Newton, Andy Sims (LBC) and Nick Tribe (LNU)

THE mysteries of bird migration came under the spotlight at a fascinating presentation at Saturday's (January 5) annual joint meeting of the Lincolnshire Bird Club and the Lincolnshire Naturalists' Union.

Guest speaker at the Whisby education centre, near Lincoln, was one of the world's leading ornithologists, Prof Ian Newton, who has researched and written extensively on the subject.

In his authoritative and entertaining address, lasting just over hour, Prof Newton showed that, even as some puzzles are being solved, other are emerging.

Depending on factors such as food abundance and climate change, migration patterns seem to be changing (at least partially) in many species - both big (such as lesser black-backed gulls) and small (such as chiffchaffs).

                                         

Chiffchaff - increasing numbers are now spending winter in Britain

Prof Newton chronicled the progress of research - ranging from the early breakthrough with ringing to ongoing developments with satellite tracking.

He acknowledged the work of German scientist Peter Berthold who, by studying sample

blackcaps in captivity, was able to identify and measure their restlessness during the migration season - the extent of relentlessness depending on whether the birds had been trapped in Sweden (high) or The Canaries (low).

Also intriguing was the speaker's account of the work done using modified radar (acquired from the disintegrating Soviet Union) to plot the enormous movements of many species of landbirds over Israel. 

These included as many as 36,000 lesser spotted eagles (pretty well the whole of the global population) within just six hours.

The pioneer of migration studies, however, was David Lack who, while monitoring aircraft movements during the 1939-45 war advised RAF colleagues that the specks that occasionally occurred on screen were bird - not angels! 

Later, Prof Newton's focus fell on the importance to migrating birds of exploiting a following wind as an aid to their journeys and how certain species, such as Manx shearwaters, will even extend their journey by hundreds of miles to take advantage of wind direction. Saving energy seems to be the prevailing requirement.

Selection of favourable wind direction may be a key factor, but birds also have to take into account risks such as thinner oxygen and loss of body heat in air than can become seven degree cooler with each additional metre of altitude.

Prior to migration, most birds build up their fat levels - with sedge warblers, for instance, doubling in size. "When being ringed, they feel like little balls of soft fat," he said.

The same applies to migratory geese, and colour ringing experiments have shown that tubbier birds - denoted by drooping bellies - enjoy greater success than their slimmer counterparts when they reach their breeding grounds in the Arctic.

Other topics covered by Prof Newton included the heights at which birds migrate - many of them beyond the scope of human vision.

Prof Newton is an expert on raptors (he has written a whole book on the sparrowhawk) and had an interesting observation to make about ospreys, noting that migration casualties - usually over the sea and the Sahara - chiefly consisted of immature birds that had "not yet  learned the ropes" of the likely hazards they would encounter.

The migration behaviour of gyr falcons is also fascinating. It seems they follow iceflows south, sometimes perching on icebergs to track their seabird prey. But then in spring they fly north and, for six weeks, probably feed exclusively on the only prey available to them - rock ptarmigans.

  

Do birds ever sleep even as they migrate?

Possibly yes. How otherwise could a bar-tailed godwit fly, without pause, for no fewer than 228 hours? It seems they can operate, as it were, on just half a brain.

Prof Newton, who lives in the south of the county, is currently researching a new book on upland birds. He is also considering a request to update one of his earlier books on migration to take in the most relevant recent research.

Following a question-and-answer session with the audience, which numbered about 60, he was thanked by LBC chairman Phil Espin for his most absorbing talk and for his "massive contribution" to ornithology.