EVERY day more migrants arrive, with sightings including night heron, hoopoe, golden oriole and grasshopper warbler.

If you see a bird you are unfamiliar with pop into Radipole Lake visitor centre or phone us and hopefully we can work out what species you have seen. If you can get a photo of the bird that really helps!

One new arrival sometimes seen at Radipole visitor centre is the common sandpiper.

This is a small wading bird with a brown head and back and white underparts. It has a habit of bobbing up and down, known as 'teetering', and has a distinctive flight with stiff, bowed wings. It will often make a three-note call as it flies off. They feed along the water's edge, pecking invertebretes from the surface of the mud.

They travel to the UK from sub-Saharan Africa and breed mainly in upland areas of Wales, Northern England and Scotland.

The arrival of migrating birds creates the usual difficulties, especially when trying to identify warblers' songs.

One way of learning calls is to come on a guided walk and this Sunday is a very special day - International Dawn Chorus Day.

So if you are an 'early bird' come and join us at Radipole Lake from 5am until 7am. A continental breakfast is available after the walk. Please contact us on 01305 778313 to book.

So why is the dawn chorus so special? Dawn is the best time for birds to sing because the air is generally calmer and sound transmission is good.

A dawn song is thought to be 20 times more effective than singing at midday and at dawn, birds can do little else. Light is poor and insect prey is not flying, so foraging for food is difficult. Also, female birds generally lay eggs in the morning, so a dawn mating is the best time for a male.

Many birds amplify their song by singing on high, exposed perches, however this also makes them visible to predators. By avoiding these predators, males can further show females their strength. During the dawn chorus, female birds listen to each song and visit each territory before deciding on a mate. As they prefer males with the most complicated songs, the males constantly develop and re-develop them.

Wrens for example, have songs that contain over 700 different notes per minute and can be heard 500m away.

Here are two more events for your diary coming up at Radipole Lake this fortnight, a wild flower wander on Thursday, May 10, 10am-noon, followed by a binocular and telescope demonstration day on Saturday, May 12, 10am-4pm.

For further information on events and a copy of the 2007 RSPB Dorset events guide visit Radipole Lake centre or phone 01305 778313.

by Lynne Burningham