To the inexperienced eye, there were no birds around. Not one. We were walking down the main street of Newbridge, Co Kildare on a blowy, grey morning. Ordinary morning things were happening. Soldiers with cocked rifles guarded a delivery to the post office. Women pushed infants in buggies. A cafe brought in its parasols before the gusts of wind could bowl them away. In that kind of weather, and in the centre of a town, you don't see birds.

Well - I don't. But I was with Brendan Kavanagh, who is among other things an ornithologist, and he sees what others don't. I met him to have my cards marked about magpies. He's an expert on magpies, and in this summer's quest to learn something about the most common birds, magpies were top of the list.

Just that minute there were no magpies around. But what there were - you only had to lift your head and look up above the lines of chimney-pots - were swifts and house-martins, wheeling and calling.

"It's a drama for them up there today," Brendan said. "Trying to feed themselves. Because the insects are speeding past them in the wind." And then he pointed out jackdaws - pure black, and the size of a pigeon - on the lookout for last night's chips and burgers. And rooks. And grey crows. And some town pigeons. For a place with no birds it had quite a lot of birds.

It turns out that the key to birds is insects. And the best place for insects on a morning of warm winds is down by a river. It was news to me that the Liffey flows through Newbridge, but there it was, just below the main street. It is quite wild on one side, with a stand of willow and poplar behind the rushes that come down to the water's edge. But on our side there was a simple path under old stone walls and whitethorn hedges, and we followed that.

There weren't, as it happened, any magpies to be seen. But the scene was full of the dot and dash of little living things going about their business. A busy waterhen jumped off a hank of pondweed in the middle of the water, in pursuit of a daddy longlegs. A group of mallard duck fiddled about in a private cove under the willows.

Past them, a grey wagtail roller-coasted along just above the water, in a marvellous exhibition of speed and control. A trout plopped up to the surface. Butterflies drifted. The river widened, and bent along beside a flowery meadow. Out in the shallows a great grey heron stood.

"Imagine looking up at that, if you were a fish," Brendan said. "Herons sometimes deliberately sway their long necks from side to side, knowing the fish will think they're looking at a reed and won't be wary . . . " Who would have thought of it! And then - colour sizzled across the greeny-grey. A kingfisher - for only the second time in my life - zipped in a flash of blue and crimson across my vision. What a thing to happen, when all I was doing was looking for the common-or-garden magpie!

Whatever local authority manages this lovely place has kept it natural and simple. The edges of the meadow shade into a tangle of long grass and nettles under the rampart hedges. Brendan paused at a tangle of dried-out bramble, overgrown by long grasses. Something was rustling around inside. Several things. He started making soft imploring sip-sip noises, probably not even noticing himself that he was doing it.

"They're wren fledglings in there," he said. "It's their first excursion out of the nest, probably. Look at their mouths. They're pale still." The chicks fluttered under the grasses. And a wood pigeon above us flew by with a stick for its nest, and tits twittered in the hedge. There was life everywhere.

Yes - but what about the magpie? At last we saw one, on the lawn of a bungalow. "Oh dear," I said. "One." But Brendan would have none of the superstition. "They get a bad press, magpies," he said sternly. "But they're one of nature's gleaners. They clean up the place. Which would you rather be," he asked impressively - "inundated with rats, or inundated with magpies?" Well, magpies.

"Furthermore," he said, "magpies probably have more intelligence, gram for gram, than your average dog or cat." They have? They have. "They also show a range of behaviour," Brendan said, "far more detailed and intricate than other birds," and he proceeded to give me example after example of magpie accomplishments.

It was what I came for. And I do feel slightly warmer towards magpies. But what I took away were: the swifts, reeling in the high wind. The scuffle of the baby wrens. And the sudden flash of glamour, when the kingfisher drew a neon line along the Liffey bank.