The cars were double-parked on Cambridge St. yesterday afternoon as the veteran customers of Mayflower Poultry Co. rushed inside to pick up their holiday birds.

"I've been coming here as long as I can remember," said Imara Soto as she loaded her two 22-lb. turkeys into her car. Soto, formerly of Cambridge, now makes the 30-mile roundtrip from Burlington each Thanksgiving just to fetch the main course for her family's get-together.

Mayflower, whose outdoor sign boasts "Live Poultry, Fresh Killed," may be the most famous place in Boston to purchase live turkeys for Thanksgiving. Yesterday, the shop's front salesroom was packed, telephones rang incessantly and trucks pulled in and out making deliveries.

Mayflower manager Dick Silver chalks it all up to freshness. "That's where the flavor is--in the freshness," he smiles, explaining that all his turkeys come from Massachusetts farms--a claim few supermarkets can match.

At $1.39 per pound, fresh turkey is no longer a bargain, but has caught on as health-conscious consumers turn away from red meat, Silver notes. While he hesitates to give specific numbers, he says that by tomorrow he will have sold "thousands" of birds.

Who opts for KYOB (Kill Your Own Bird)? "That's strictly an ethnic thing," says Mayflower manager Dick Silver. "The Chinese people buy it, the Portugese, the Italians. Otherwise, it's a dying industry."

Indeed, progress is making it nigh impossible to make a killing in the live turkey market these days, Silver says. "The people today don't require it unless they grew up on a farm or something. Then they know that fresh is much better."

And while one might think that a person who makes his living on fowl might opt for a Thanks-giving roast, Silver says that's not the case.

"No, it's tradition. I have to take one home tonight as a matter of fact, if I don't forget."

SELLING only 300 turkeys a year, Sage's market on Brattle St. can't match Mayflower's volume. But manager Dwight D. Perodeau was able to offer some insight into turkey farming.

"The turkeys are really pretty dumb. About 10 or 12 guys with these things that look like featherdusters drive them into the killing shed. They have this golden opportunity to get away, but they don't," he says.

"The biggest [turkey] runs around 26 pounds. Most people buy in the neighborhood of 12 to 16 pounds."

Perodeau says the turkeys are put down by mechanical means. "My understanding is that they use an electric knife. They hang them up by their legs, cut their jugular veins and let all the blood drain out. It gives them a nice golden-yellow color."

But, says the manager, even retail grocers are not permitted to see the parts of the farm where slaughtering takes place. "They don't let you see the actual killing process. But that's just as well, I suppose," Perodeau says.

Kate E. Huston, a UMass student and Sage's cashier, says some customers pass over turkey for less traditional holiday fare.