Wildlife experts have said plans to build 10,000 new homes in West Sussex could destroy a habitat for nightingales.
The proposed new market town near Henfield also includes schools and shops.
The British Trust for Ornithology said it feared it would leave the birds and other species with nowhere to go.
Developer Mayfield Market Towns said it would not be allowed to develop without looking at the ecological impact.
Resident Jane Simmons, who is fighting the proposals, said she regularly slept with her windows open to hear the nightingales singing.
"If people knew about it they'd probably be flocking here with their binoculars to see what we've got," she said.
"It would be a tragedy for it to be destroyed."
Mike Russell, from Sussex Wildlife Trust, added that the site was "a mosaic of habitats", with water meadows, a network of hedges, small woodlands and agricultural areas.
"It's a real mixture of habitats in a fairly confined area and that gives it a lot of diversity," he said.
In a statement, Mayfield Market Towns Limited said: "We have already employed ecologists to carry out preliminary studies, and the next stage will be to conduct more indepth ecological studies which we will be consulting on at a later stage.
"This is all part of the normal planning process and we wouldn't be allowed to develop without showing that we have looked at our ecological impact."