NATURE NOTES - Coming and going

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MID September is one of those times when incoming and outgoing birds cross each others paths!

We had a day on the coast ‘wader watching’ this weekend and it was interesting to see thousands of pink footed geese out on the saltmarsh being overflown by hundreds and hundreds of swallows heading south on their journey to warmer climes – in a similar way that the pink foots were doing too.

The band of high pressure at the weekend had literally thousands of bird arriving and thousands of birds leaving the UK. I say it every year but the journeys these birds make are mind boggling to say the least! European swallows spend the winter in Africa south of the Sahara, in Arabia and in the Indian sub-continent. British swallows go further south and spend their winter in South Africa: they travel through western France, fly over the Pyrenees, then down eastern Spain into Morocco, and across the vast waterless Sahara. Some birds follow the west coast of Africa avoiding the Sahara, (sounds like a good idea) and other European swallows travel further east and down the Nile Valley.

Migrating swallows cover 200 miles a day, mainly during daylight, at speeds of 17-22 miles per hour. The maximum flight speed is 35 mph. So as you can imagine it takes a while to fly to South Africa. I could never understand why they fly all that way backwards and forwards (up to eight times in a swallow’s lifetime) when there are more than enough insects to go around in summer and winter in South Africa.

Migration evolved as a way for birds to exploit resources that are seasonally abundant and, equally important, to go elsewhere when the resources become scarce or harsh weather arrives. However, many species can tolerate cold temperatures if food is plentiful; when food is not available they must migrate. While this simple explanation is essentially true, intriguing questions remain. One puzzling fact is that many birds journey much further than would be necessary to find food and good weather. Presumably, British swallows could survive equally well if they spent the winter in equatorial Africa instead of South Africa’s Cape Province. So why do they do it? To be truthful I have no idea I’m just so glad they do – what would an English summer be without a swallow!