Wild Things columnist Eric Brown passes on some excellent advice about keeping an open mind when birdwatching and invites readers to participate in the largest annual UK citizen science project.

MANY years ago a wise old birdwatcher gave me some treasured advice. He counselled me to keep an open mind and expect the unexpected when birdwatching.

He added that I should believe any bird could turn up anywhere. "Think AA," he said. "Anything anywhere." I am not sure I originally accepted this little nugget as seriously as I should have done. Later though, I found it invaluable.

It leapt back into my mind recently but only after I shamefully ignored it.

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Six searches of a stretch of Kent coast failed to yield the purple sandpiper I was seeking. About 9,000 visit Britain from Greenland and Norway each winter. They love rocky coasts where they scamper around wave-splashed rocks and wooden groynes snapping up food morsels as they are washed in. I've always regarded them as exclusively birds of rocky seashore. But bear with me, dear reader. I knew there was a purple sandpiper on this stretch of coast because I'd been told of its presence among sanderling and turnstones by other birdwatchers. "Just over there, you can't miss it," explained one, pointing to the beach. After the sixth occasion painstakingly scanning through about 300 waders sleeping on the beach I gave up deflated. On the return walk several turnstones were feeding busily in a caravan park field opposite the beach. And there among them was the purple sandpiper! I had never before seen one in a field. They probe among seaweed and rocks for molluscs, sandhoppers, winkles, mussels, shrimps, crabs and anything else the tide brings in. So what was this bird eating in a field ? I have no idea. But the experience brought to mind the old Anything Anywhere mantra and I admonished myself for passing this spot several times so focused on the beach that I hardly spared a glance for birds feeding in a field. I didn't think AA.

Anyone settling down to take part in this weekend's RSPB Big Garden Birdwatch should keep the AA advice in mind. You are unlikely to have a purple sandpiper visit but you never know what might turn up in the garden. Mine is a pretty ordinary suburban space with grass and shrubs but no mature oak or birch trees to interest a great spotted woodpecker. Yet one spent some time perched on a fence. There's no running water anywhere nearby yet a grey wagtail appeared and I have no bramble yet a whitethroat once spent time exploring the garden.

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If you haven't taken part in this 40-year-old RSPB survey before, it is simple. Just set aside one hour over the period January 27-29 to record the birds you see in your garden during that hour. You can complete the task from an armchair while looking through patio windows. If you don't have a garden you can nominate a park, waste ground, wood or playing field. This is the largest citizen science project in the UK with around half a million people involved each year. Records provided by participants and analysed by the RSPB can indicate dramatic population falls like those of house sparrow and song thrushes in the past. Greenfinch numbers have declined recently and it will be interesting to see how this species fares. The RSPB will be interested even if you see nothing.

For more information on how to obtain a form or enter sightings online by February 14, go to rspb.org.uk/birdwatch.

And remember to think AA!