Every fortnight for the last 16 years staff at Cruzinha have counted the waders on the estuarine marshes at low tide. This is an amazing record that enables biologists to pick up changes in population numbers as patterns emerge in the data. The Quinta da Rocha headland conveniently divides the marsh into two sections. It takes about two hours to count each side and Clare and I helped Bebe with the easterly marsh.

On the way to the count there were azure-winged magpies calling in the trees - more secretive than their pied cousins, but with the same raucous squawk. We crossed a couple of fields to the riverbank and worked our way to the sea, recording as we went. Bebe had a telescope on a tripod and she did most of the bird identification. She gave me a clipboard with a recording sheet that had the marsh divided into numbered zones. It wasn't a regular grid but a plan divided according to the shape of the mudflats and islands.

The largest waders that we saw were black-winged stilts, easily recognisable with their stunning plumage and balancing on a pair of long knitting-needle legs. The small waders were also in evidence, mainly dunlin and little ringed plovers. We heard the evocative call of a curlew flying in the distance, though we didn't manage to see it. Other birds that we saw were little egret, grey plover, knot, greenshank, redshank, black-tailed godwit, avocet, sandwich tern, little grebe, teal, mallard, shoveller, common sandpiper, and moorhen.

From the headland we looked down on the western marsh and saw two pairs of flamingos - not the variety that match boiled prawns, but white flamingos, though they were a dirtier colour. We heard quail, saw partridge, and on the walk back we saw a woodchat shrike and Sardinian warblers.

As we walked I contemplated the difference in the two banks of the river. We were on the unspoilt marsh, but on the other side of the estuary was the town of Alvor, with older traditional buildings giving way to high-rise apartments. The Quinta da Rocha headland is a wonderful oasis for wildlife amid the commercialisation brought in by tourism.