The Worldwatch Institute reports that a growing number of US city-dwellers are raising their own chickens, often in defiance of local ordinances.

Citing unsanctioned henhouses in Denver, Boston, and other cities, Worldwatch's Ben Block notes that an "underground 'urban chicken' movement has swept across the United States in recent years," flouting authorities' concerns about noise, odors, and public health.

But in some cities, such as Ann Arbor, Mich., Ft. Collins, Colo., South Portland, Maine, and Madison, Wisc., owners of these clandestine coops have successfully changed the laws to allow them to keep a limited number of hens. (Roosters, whose characteristic crowing can disturb neighbors, are usually more restricted, but they're not needed for hens to lay unfertilized eggs.)

Many large US cities, including New York, San Francisco, Los Angeles, Houston, Chicago, and Seattle apparently never thought to ban the domesticated fowl within city limits. These cities have served as an incubator of sorts for the emerging movement, in which urban henkeepers post online tips on building coops, caring for the birds, and fending off raccoons and other predators.

Laws vary from city to city. The City Chicken, a popular urban chicken website, maintains a list of local laws, but it is far from comprehensive. Municode.com also keeps a list of ordinances for selected cities. In many cities, would-be chicken owners need to obtain a permit from local health or animal-welfare authorities.

The benefits of keeping hens are myriad, say proponents. According to the website BackyardChickens, considered authoritative in the online urban-chicken-enthusiast pecking order, three hens will net you, on average, two eggs a day. And the eggs are said to be tastier and more nutritious than the ones you can get at a supermarket. Hens also perform some gardening work by eating weeds and pests and depositing a high-quality fertilizer. Many also claim that the birds make great pets, but this is debatable.

Urban chicken buffs also claim that, once you're all set up, the birds are relatively low-maintenance. The UK-based company Omlet sells popular ready-made coops starting at about $500. Their "Eglu," which looks like a late-90s Macintosh computer, comes with a chicken run and a feeder. Chickens can be purchased separately from the company for $15 each.

Some, but not many, urban henkeepers opt to raise their chickens indoors. The birds cannot be toilet trained, but at least one company sells chicken diapers.

The blog Urban Chickens gives a rundown of the regular maintenence required to keep your chickens well-fed, comfortable, and odor-free. The blogger says his routine goes like this:

• Every day: fill the food bowl, change the water, check for eggs, add wood chips to the nesting box if needed. (takes 5 minutes)

• Twice weekly: empty the droppings out of the Eglu, very easy to do by design, thanks Omlet! (takes two minutes)

• Weekly: clean the Eglu by rinsing and scrubbing the interior parts (20 minutes)

• Semi-monthly: purchase 50-lb. bag of Layena Crumbles at the feed store (cost is $12 and is worked in with other errands)

A hen's productivity will drop off after two or three years. After that, the hens will continue to produce high-quality eggs, but at a slower rate. Those who wish to eat their chickens (that is, people who dispute the assertion that they make great pets) should know that in many cities different laws apply for chickens raised for eggs and those raised for slaughter. For those too squeamish to do the deed themselves, some communities have mobile slaughterhouses that will come to your home and do it for you.

The rising popularity of urban chickens has many city officials brooding over public health concerns, particularly avian flu (of which there have been no reported cases in the United States). According to Worldwatch, officials have threatened to restrict poultry in cities in East Asia, Australia, and British Columbia. Worldwatch also cites an expert who advises owners to keep their coops covered to protect their chickens from wild bird dropppings, which are said to transmit the disease.

But others argue that chickens are no more likely to carry the disease than, say, pigeons, which are already common in cities. What's more, as Worldwatch points out, the Pew Commission on Industrial Farm Animal Production found that factory-farmed poultry poses a greater risk for the disease than backyard chickens.

In many cities, the policies regarding domestic fowl are by no means settled. In September, the Boston Globe reported on a Lynn, Mass., man's battle wth "loosey goosey" laws over his chicken coop. And this YouTube video, posted in July, has several Chicago officials on tape falsely telling an aspiring chicken owner that the birds are prohibited within the city.

This kind of ambiguity could mean more and more henkeepers unwittingly finding themselves on the wrong side of the law. As the urban chicken movement spreads, local authorities will have to set clearer policies to help those chicken owners get to the other side.