BIRDWATCHERS are being asked this week to keep a special eye open for the whitethroat, whose jerky flight and scratchy song are a feature of scrub, young woodland and hedgerows.

The whitethroat, another common summer visitor from Africa, is the "Bird of the Week" in the British Trust for Ornithology's Internet-based bird migration census, the first ever to make use of the web - and one in which anyone can take part.

The Whitethroat has experienced dramatic crashes in its population in the past. These crashes are due to climate related changes in its African wintering grounds. In spring 1969, three-quarters of the Whitethroat population failed to reappear in the UK. After a low point in the population in 1974, numbers steadily increased before crashing again during the winter of 1984/85. Since then the population has stabilised.

The catastrophe also affected other species that winter just south of the Sahara such as sand martin. Drought conditions in the Sahel can have a massive impact on the fortunes of migratory birds. You can help track the arrival of Whitethroats this spring by logging onto the BTO website www.bto.org/migwatch to record arrival dates.

For more information on Whitethroat see www.bto.org/migwatch and click on 'Focus on Species'.