Lively chat show
MIGRATION on full power is always pulsating but nothing has given me a buzz quite like experiencing a recent redstart son et lumiere.
There were the fiery red tails of arguably our most beautiful chat, flicking and flashing everywhere as birds heading for the tropics fattened up on a newly ploughed field.
From lofty perches in a sunlit hedgerow, the redstarts were detecting the wiggles of hapless bugs then swooping down to catch them for breakfast. Up to six redstarts in a variety of plumages, from the subtle shades of a young female to fullblown, dandy males in hues of gun metal blue and burnished copper, sparked a pyrotechnic show.
At rest, the birds would declare their presence deep in berry-rich hawthorns with plaintive calls as if urging other migrants to enjoy the rich pickings.
Fuelling trans-continental flights is a life-or-death struggle for birds but, unlike the hormone-charged spring flights to nesting grounds, autumn is a more leisurely affair. This allows them to rest over and benefit from sugar-rich fruits or invertebrates becoming increasingly lethargic with cooling temperatures.
During pauses in the redstart spectacular, there was chance to watch the darting flights of spotted flycatchers and muse over the varied plumages of yellow wagtails from shades of sunshine to those in solemn greys. Wheatears, whinchats, swallows, house martins and a variety of warblers brought back memories of witnessing migration in Moroccan oases and Israeli wadis.
Undoubtedly, the most electrifying moment came when I adjusted my telescope while standing directly under a high-power transmission line. As I moved the tripod, I could feel the electricity throbbing through its steel legs, reminding me of physics classes, Van de Graaff generators and hair frizzing like Albert Einstein’s wild mop.
Studies show birds have proteins in their eyes called cryptochromes which allows them to detect magnetic fields. So while I was abuzz with an electrical charge, I began pondering whether power lines have an impact on the routes they choose.
I put the question to the British Trust for Ornithology’s migration expert Paul Stancliffe. He told me how birds have a number of tools to help them, including an ability to detect and visualise the Earth’s magnetic field as well as seeing polarised light to detect the sun on a cloudy day.
Smell provides clues to stopover sites and eventual destinations while, like ancient mariners, stars point nocturnal fliers in the right direction. There are also daytime visual clues such as rivers, roads and mountains.
“During a ‘normal’ migration, when the weather is kind, they probably use all of these but what is unclear is whether any one of these tools is dominant and used in preference,” Paul continued.
“So, it might be that migrating birds could be attracted or disrupted by high-voltage power lines and their electro-magnetic fields, or they could be using them as visual cues, following them like a line on a map.
“Until we know how migrating birds navigate, it is impossible to say if man-made electro-magnetic fields affect them. There more work to do.”
‘Birds visualise magnetic fields’
Sharp-eyed readers were quick to spot last week’s identification faux pas. Rather than an osprey, I used a photograph of a red kite.