To do this, the service asks that day-old poultry be shipped early in the week. That way, birds won't get stuck at a post office over the weekend or a holiday.
Likewise, if the weather is unusually bad, the postal service can deny shipment, according to regulations.
Ann Chynoweth is the director of the Humane Society of the United States campaign against animal cruelty and organized animal fighting, such as cockfighting.
(See a photo of cockfighting in Thailand.)
Chynoweth said the Humane Society has seen an increase in complaints from postal workers who are concerned about dead and dying birds in the mail.
"They are distraught at not being able to do anything about it," said Chynoweth, who is based in Washington, D.C.
As an example, she cited an anonymous letter from a postal worker in Minnesota who said 24 dead chickens showed up at a mail-sorting facility when it was 3 degrees Fahrenheit (-16 degrees Celsius).
"All of them were dead," the letter said.
The Postal Service's Anderson says the U.S.P.S. responds to all service issues or problems raised. He adds that he cannot directly respond to the complaints cited by the Humane Society because they are anonymous.
"It's in our best interest [to respond]. And I'm sure the shippers and buyers want their product to arrive in good condition," he said. "If there's a problem, we respond immediately."
The Humane Society is asking the U.S. Postal Service to require more humane conditions for the birds, such as only shipping between 50 and 90 degrees Fahrenheit (10 and 32 degrees Celsius) and limiting truck or car time to four hours.
"We don't think animals should be treated as [just] any other package," Chynoweth said.
U.S. Senator Chuck Grassley, an Iowa Republican, introduced legislation on March 9 that would require mail carriers to carry birds when the temperature is anywhere from 0 to 100 degrees Fahrenheit (-18 to 38 degrees Celsius).
The legislation would also make denying live bird shipments harder for commercial airlines and couriers that accept U.S. Postal Service contracts.
For example, FedEx, a postal contractor, does not accept shipments of any live animals "as part of regularly scheduled service," said Carla Boyd, a company spokesperson in Memphis, Tennessee.
According to Boyd, shipping animals requires special arrangements and specific configurations that interfere with FedEx's regular operations.
FedEx's policy currently permits it to refuse shipments of baby chickens.
By contrast, commercial airlines with postal contracts are obligated to accept live-bird mail shipments. Since the airlines already ship passengers' birds as cargo, mailed birds should not interfere with the airlines' regular operations, the thinking goes.
According to Bird Shippers of America, a lobbying organization for the hatchery industry directed by McMurray, the new legislation would force FedEx to accept baby chickens because the courier does transport some live animals.
"FedEx does carry all types of animals, except dogs, cats, and bees. Consequently, the [proposed] provision states that if the air carrier transport[s] any animals by cargo, it must take birds by air mail," reads a statement on the Bird Shippers' Web site.
The Humane Society says it is also concerned that the transport of millions of birds "is a risk in the threat of avian flu," Chynoweth said.
The animal-welfare organization fears that if an outbreak occurs among mail-order chickens, it will be hard to find and kill the infectious birds, because they spread so rapidly around the United States. (Killing all infected birds is considered the best way to curb an avian flu virus's spread.)
McMurray, the hatchery owner, said such fears are unwarranted, since there is no bird flu in the U.S. And fears of bird flu, he added, have not impacted his business.
"With all the publicity that is constantly in the press on a nearly daily basis, I thought for sure it would, but it has not," he said.
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