PESCADERO — When Gary Strachan heard that a rare yellow-hooded warbler had been spotted flitting across a nearby farmer's field, thousands of miles away from its typical winter habitat, he had to see it for himself.

When he visited the field on Dec. 30 with a group of other birders, he was amazed by what he saw: Not only was the hooded warbler there, but so were hundreds of Townsend's warblers, yellow-rumped warblers, Ruby-crowned kinglets, killdeers, blackbirds and several types of sparrows — all chirping, hopping and feeding themselves silly on thick mounds of decomposing Brussels sprouts.

The birds, some of which are nearly as rare as the hooded warbler, have been surviving the cold snap by feeding on an unexpected banquet of fly eggs laid inside the warm piles of excess Brussels sprouts composting along the edges of the sunny field.

News of the riotous, colorful display at Cascade Ranch, just north of Ano Nuevo State Reserve, spread quickly after the initial discovery was made during the Audubon Society's annual Christmas Bird Count. Details were posted on Bay Area bird-watchers' Web sites. By Jan. 5, a caravan of cars belonging to bird lovers and bird photographers were parked along Highway 1. They haven't let up since.

"I've never seen anything like this in my 23 years here. These birds are just really gorgeous little jewels," said Strachan, head ranger at Ano Nuevo and an avid amateur birder who said he is only too pleased to have people from as far away as San Jose or the East Bay discover the area.

The profusion of birds at the site, numbering as many as 300, is essentially due to chance. The birds have benefited from the accidental placement of the excess Brussels sprouts near the willow trees and blackberry bushes that line the edge of the field near Cascade Creek.

Farmer Nando Muzzi, who leases part of the 400-acre ranch from the nonprofit group that owns it, said he has been composting Brussels sprouts on this field for 30 years. This year, however, was the first time he put the Brussels sprouts within swooping distance of the trees and bushes. He was as surprised as anyone when the birds came in such numbers this year, he said.

"They get good coverage there. They're cute little birds," said Muzzi. "We try living in harmony with the things around there. Otherwise, it wouldn't work."

On Sunday morning, at least a dozen photographers and birders stood around the site in awed, respectful clusters as 10 species of birds hopped around each other, showing off their colors in the sunlight.

San Carlos resident Ron Thorn looked through a pair of binoculars. Known among birders for spotting rare birds in San Mateo County, he confessed that even he was astonished to see so many kinds of birds in such a concentrated area, and so exposed.

"I may not see this again in my lifetime," said Thorn. "You never know what else is out there that nobody else has seen. It's kind of overwhelming."

To some environmentalists, the birds are more than just a pretty sight — they're a lesson in how farming can benefit wildlife instead of hurting them.

"For a long time, people have put nature and agriculture on opposite poles, and that's not the case at all. There's a knowledge base that needs to be developed about how to work with both," said John Wade, executive director of Cascade Ranch Historic Farm, the nonprofit that owns the land Muzzi farms.

The accidental bird phenomenon fits handily into the nonprofit's mission, which is to cultivate an interdependent relationship between commercial farming and enhanced habitat protection on the property. The group hopes eventually to convert the farm into an organic operation.

Meanwhile, it will restore wildlife habitat by planting trees and establishing irrigable ponds that will also benefit snakes, birds and amphibians.

Wade said the group will spread the Brussels sprouts along an even longer stretch of field bordering on the bushes and willows next year, a decision Strachan approves of.

"If the agricultural community understands this now, there's an opportunity to do this every year," he said.

Staff writer Julia Scott can be reached at 348-4340 or jscott@sanmateocountytimes.com.