BIRDS flocking to the northwest New Territories are being squeezed into an ever-decreasing parcel of land by development projects, putting the area's regional importance as a migratory centre under threat, according to green groups. The latest hazard comes from the Shenzhen River widening which is intended to alleviate flooding but will affect bird habitats. Eagles, owls and other birds of prey inhabit the Seung Ma Li Yu hill between Lok Ma Chau and Lowu which is proposed to be chopped down. A number of other birds feed in the fishponds that will be filled in by dredged sediment from the river, much of which is expected to be polluted. Green groups say the river widening is only the latest project to put birds at risk, as housing, container storage, Route Three and mostly-uncontrolled development in Shenzhen gobble up the fishponds where they feed. About 40 per cent of wetlands could be lost from the cumulative effects of these projects, according to the World Wide Fund for Nature. Lew Young, the fund's manager of the Mai Po nature reserve, said the wetlands were a source of food for migratory and local birds and the area was one of the only preserved wetland sites on the south China coast. But herons have abandoned at least one breeding colony, probably because of the loss of the fishponds from which they feed, he said. About 150 to 200 pairs of herons used to breed at Mai Po village near Castle Peak Road, but they have now moved into the nature reserve. ''A lot of fishponds are filled in and those not filled in are disturbed by development. If the birds can't feed, it doesn't matter if their nesting grounds are safe,'' Mr Young said. Some 55,000 water birds stopped off in January in Mai Po. The 17-kilometre Shenzhen River project is a worry because much of the impact has still not been assessed. The loss of fishponds and trees will be compensated for with wetland allocation elsewhere and re-planting, according to Mak Ka-wai, senior engineer of special projects in the Drainage Services Department. But Lisa Hopkinson of Friends of the Earth said it was impossible to look at the first stage in isolation, particularly as the latter two stages are expected to have a greater impact and will affect Deep Bay. The World Wide Fund and Friends of the Earth said it was crucial that the international Ramsar Treaty on preserving wetlands be extended to Hong Kong.