Travelling on the wing
Many of us enjoy holidays abroad and nearly all of us get there by plane. However, consider the birds of the air and some of the insects, many of which travel similar long distances to humans, yet they do it entirely under their own steam. One of the joys of spring is seeing the first swallow. These birds, weighing only two-thirds of an ounce (18 grams), travel all the way (over 6000 miles) from South Africa, arriving in April having flown over the 2000-mile-wide Sahara Desert, probably the most dangerous stage of their journey. Some adult swallows live to nine or ten years old, having flown to South Africa and back every year, and raised 8 to 10 fledglings during the summer.
Modern technology has revealed much about bird migration routes. Satellite-tracked cuckoos are now known to head either southwest through Spain or southeast through Italy before crossing to Africa. However, the truly baffling question is - how does a young cuckoo, raised by meadow pipits in a nest on Dartmoor, and having never seen its true parents, know that it has to fly south in autumn and find its way to exactly the same area – the Congo rainforest, south of the Sahara – where the rest of British cuckoos spend the winter. How amazing is that!
One of the last summer visitors to arrive is the spotted flycatcher. Recent studies in South Devon and elsewhere using ‘geolocators’ have shown that ‘our’ birds winter in Africa in the area around Gabon and the Congo, but mainly in Angola. Geolocators are tiny tracking devices that record light levels and time and are usually attached to the back or legs of birds; the data they collect enables scientists to calculate where the birds have spent the winter.
Small numbers of golden plovers used to breed on Dartmoor; 17 pairs bred in the late 1970s, but numbers gradually declined and they last bred on the moor in 2004. Now flocks of them, sometimes hundreds, can be seen regularly on the moor in winter, but these travel north in late winter/spring to breed in northern England and Scotland. Another scarce migrant which still breeds on the moor, ring ouzels can be found in a few valleys on Dartmoor; in late autumn they fly south to sunny Morocco where they spend the winter feeding on juniper berries.
After conifer plantations were introduced, siskins first bred in mainland Devon in 1957 and they now regularly visit some gardens. However, those you see in winter may well have come from Scottish breeding sites. Another formerly common garden bird, the greenfinch, now sadly much scarcer due to trichomonosis, was found (through ringing) to winter in Devon and Cornwall and then travel northeast in spring to breed in south east England. Not all migrant birds move great distances; some are known as ‘partial migrants’ and only part of the population migrates. For instance, British goldfinches, now common garden visitors (especially to gardens that feed nyjer seed or sunflower hearts) migrate a few hundred miles south and winter in France or Spain.
Birds are not the only travellers as some insects also migrate astonishing distances. A recent TV programme about painted lady butterflies showed that they breed in North Africa in early spring, then the young fly north to Spain where they breed again. Successive generations then migrate north and breed, eventually ending up in northern Scotland. Two day-flying moths, the hummingbird hawk-moth and the Silver Y, both of which are long-distance migrants from southern Europe or North Africa, are often seen in summer visiting the flowers of honeysuckle and buddleia. Other moths which migrate from abroad include the dark sword-grass, diamondback moth, rush veneer and rusty-dot pearl, the last three of which are ‘micro’ moths.
Tony John