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  Swallow
   

SEPTEMBER - SWALLOWS

One swallow might not make a summer, but you definitely won’t find any swallows at all during the British winter. A sure sign that colder weather is on the way is when football replaces cricket on the TV, and swallows gather excitedly to leave Britain for warmer climes. As we look out our gloves and scarves, and put the lawn mower into hibernation, our swallows begin the 6,000 mile journey south to spend their winter in South Africa.

MIGRATION

One minute they are gathering together, both adults and young swallows unmistakably excited about the unknown journey ahead. The next the telephone wires and skies are empty as they leave us for another year. We will see some again next April or May, but many will never return. For migration is a hazardous time and many birds die from starvation, exhaustion and during bad weather.

SwallowTypically leaving us in September (the precise timing of migration each year is governed by weather and food availability), they travel through western France, across the Pyrenees and down eastern Spain.

By October, they have crossed the Mediterranean near Gibraltar and reached Morocco. Then begins the long journey across the Sahara Desert, continuing south through Algeria, Niger and Chad to cross the Equator and reach the Democratic Republic of Congo in November.

Some birds prefer to follow the longer west coast of Africa to avoid the Sahara Desert, while other European swallows travel further east and down the Nile Valley. They journey onwards to arrive in South Africa just in time for Christmas. Migrating swallows can cover up to 200 miles a day, at speeds of about 20 miles per hour.

They migrate during daylight at low altitudes and find food on the way. They don’t put on much extra weight before migrating, so despite accumulating some fat reserves before crossing large areas such as the Sahara, they are very vulnerable to starvation.

Million of birds take flight each Autumn as internal signals – triggered by shorter days, waning food supplies and harsher weather herald hard times to come. Prompted by climate and landmass changes at the end of the last ice age, this migration is at least 15,000 years old and still evolving. The impacts of global warming on local environmental conditions are already influencing when and where some birds go. But general migratory patterns are deeply ingrained and change takes time. Just how quickly migration routes will evolve to meet the future is still up in the air (excuse the pun!).

What’s remarkable is how they do it, navigating by an internal magnetic compass and external markers – stars, mountains and rivers for example.

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RECOGNITION

Swallow Swallows are distinctive birds and readily recognisable. They are quite small with dark glossy blue backs, red throats, pale under parts and notably long tail streamers.

In flight, the swallow is most agile and graceful. Its effortless twisting and turning in search of food is a delight to watch, and they spend most of the time in the air.

The long tail is used to good effect to accomplish intricate aerobatic manoeuvres to catch insects.

POPULATION

Results from recent surveys indicate that swallow numbers have declined quite markedly in some parts of the country. There are generally estimated to be around 375,000 breeding pairs in the UK, but populations fluctuate from year to year and are affected greatly by weather. They require rain for wet mud for nest building and for encouraging the abundance of insect prey, but cold wet weather prevents them from feeding. Large scale mortality is regularly recorded during and after bad weather, during both breeding and migration. On the other hand, hot and dry weather can result in mortality through dehydration and heat stress.

Setting aside weather-related fluctuations, there are believed to have been widespread declines in Europe since 1970. The swallow is included on the Amber List of Birds because of concern across Europe about its conservation status. For more information, download "The State of the UK's Birds, 2002" (PDF file, 749k), click here.

Possible explanations for the decline include the following.

  • Climatic changes in the swallows African winter quarters and on migration routes may be having a serious effect. Research has shown that swallows are returning to their breeding areas in poor condition and are laying fewer eggs than previously.

  • Adverse climatic conditions in Europe may also be having a detrimental effect. Cold springs with late frosts in May and early June cause problems for swallows, as do very hot summers. In the latter case, pools dry out, reducing the numbers of emerging insects, and nestlings die from heat exhaustion and dehydration.

  • The continuing spread of the Sahara Desert may be making this formidable barrier increasingly difficult for swallows to cross.

  • Changes in farming practices throughout Europe may be reducing the numbers of nest sites and flying insects.

If we are to conserve bird populations, then we need to understand, among other things, how climate change might be affecting migration strategies. For more information, visit the BTO Appeal website.

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ENCOURAGING SWALLOWS TO NEST:

We can do much to encourage swallows to nest, as they are happy to live close to humans. For anyone with an interest in nature, the pleasure of seeing them close up every day is hard to beat.

They prefer outbuildings which provide dark ledges and nooks and crannies for nesting. These are cosy in cold weather and cool when it is hot. Swallows can enter a building through a very small hole and need very little light. Brightly lit nest sites are most at risk from predators. Pairs can occupy the same building with nests as close as a yard apart.

To help them to nest in a garage or outhouse:

  • Make a small opening, 50 mm high and 70 mm wide, under the garage or barn eaves or leave a window or door open

  • Fix a nest platform where you would like them to nest, high in the building, out of the reach of cats

  • Make a platform from four flat pieces of wood, or by fixing a sawdust and cement or papier-mache cup to a wooden backing plate.

  • Put a plastic bag below the nest to catch droppings

  • Block off sites where you don’t want the birds to nest, for example by attaching polythene to a beam, then to the roof and back to the beam again

  • If the weather becomes very hot, place an old carpet or blanket on the outside of the roof above the nest and soak with water regularly. Just a couple of buckets of bathwater on such fabric will take several hours to dry and helps keep the temperature down inside.


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Links and Sources for this feature:

RSPB website

BTO website

Audio and video

How many swallows make a summer?

Birds of Britain website

RSPB swallow wildlife information leaflet (2002)

National Geographic Magazine



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