Basin Notes - February 2012

The wonder of bird migration

Humans have always been fascinated by bird migration, a natural phenomenon which sees half the world's avian population making amazing journeys in spring and autumn. Recently I watched a flock of knot and bar-tailed godwit feeding at Montrose Basin and was reminded of the spectacular long distance migrations that these two species make.

Knot are about the size of a blackbird and in winter are grey-looking with white underparts. They feed mainly on molluscs in which the basin is rich. Watching birds on an estuary is always enhanced by a flock of knot, tilting and wheeling in close formation. On a bright day their aerial manoeuvres are quite spectacular as the shimmering mass of bodies catches the sun.

Around 70 per cent of the race Islandica spend the winter in the UK. During April and May these birds will fly to Iceland then on to the east and west coast of Greenland to breed. Thousands more will travel even further, flying over Baffin Bay to secure their breeding territories in Arctic Canada.

Before their migration starts, they will gorge on molluscs and may double their body weight to sustain them during their long hops between coasts and estuaries. Their winter plumage of grey and white is transformed in summer to brick red feathers on their head, neck, chest and belly with their back and wings taking on a black and beige spangled appearance - a handsome bird indeed. Populations of knot are widespread and can be found in South America, South Africa and Australasia.

Bar-tailed godwits are long legged waders with long slightly upturned bills. They are halfway between redshank and curlew in size and often feed in deeper water for lugworms, ragworms and shrimps. Their winter plumage is greyish-brown and like knot they look a different bird in summer with their dark rufous head, chest and belly.

In spring they will leave the UK and head along the west coast of continental Europe and on to Scandinavia and northern Russia to breed. Some Alaskan breeders fly all the way to New Zealand for the winter. A female bird fitted with a satellite tracking device has gone in to the record books by flying non-stop from Alaska to New Zealand over the Pacific Ocean.

The 7,300 mile journey took eight days and was completed without any food being eaten as these birds cannot feed on the wing. Miranda, as she was named, (after the New Zealand village where her tracking device was fitted) became a media celebrity during her eight-day journey and the bells of Christchurch cathedral were rung when her amazing flight of endurance was completed.

Before their pre-flight migration, bar-tailed godwits become morbidly obese, like butterballs covered in feathers. They can also internally absorb portions of their organs which are not required during the flight. This leaves space within their bodies to take on extra fat. On reaching their winter quarters the organs will regenerate and become fully operational again. Quite amazing really.

We marvel at what has already been discovered about life on our planet and I am sure Mother Nature has many more secrets tucked under her wing.