In a vacant lot beside the railroad tracks, 20 donkeys wander behind a wire fence, munching carrots and leftover tortillas and waiting for pats on the head from the occasional tourist.

This shelter for unwanted donkeys would have once seemed a laughable idea in Mexico, where the hard-working burro is practically a national symbol, manager German Flores says.

But Mexico's donkeys are quickly being replaced by pickups and tractors even in the poorest areas, prompting efforts to save the unwanted animals and to remind Mexicans how much their country owes to these beasts of burden.

"People love them, but there's not as much work for them anymore," says Luis Huerta, a member of the Donkey Sanctuary of Mexico, a group of veterinarians that helps the Burroland shelter.

An important part of history

Mexico's donkey population has plummeted to 581,000 in 2007, from 1 million in 1991, according to Mexican government statistics. Many are killed by their owners or end up in slaughterhouses, Mexico's Society for the Protection of Animals says.

It's a sad end for an animal that once thrived in Mexico. Burros — a Spanish term for medium-size donkeys used as pack animals — were brought to the New World by Spanish colonists, says Leah Patton of the American Donkey and Mule Society.

Otumba, 45 miles northeast of Mexico City, became a major animal market. Burros sold here hauled silver and gold from mines, bringing wealth to the Spanish empire. They also carried silks and spices from the Pacific Ocean to the Atlantic as part of the trade route to Asia. They accompanied pioneers pushing west and north through the Americas.

"These are animals that basically built the continent," Patton says.

Mexican speech and culture is full of references to burros, from the "burrito" style of soft taco to "Burro 16," a game known as leapfrog in English. Every weekend, thousands of Mexicans cheer on the White Burros, the sports teams of the National Polytechnic Institute, Mexico's second-largest college. Burros painted like zebras have become a kitschy tourist attraction in Tijuana.

Otumba holds an annual Burro Festival in late April and early May, with donkey races, a costume contest for donkeys and games of burro polo.

In most parts of Mexico, burros are associated with backwardness and rural poverty, Huerta says. As Mexicans become wealthier, many farmers are getting rid of their animals.

"They're not even worth 500 pesos ($38) these days," Flores says. "The people who have burros are peasants over age 60 who still value the animal's work. The newer generations prefer a pickup or a tractor to a burro."

Efforts to protect the burro

The burros' fate has inspired some action to save them. Donkey Sanctuary sends a mobile veterinary clinic around the country to treat the animals for free because farmers no longer want to spend money caring for them.

The Mexican Society for the Protection of Animals is campaigning to bar the killing of unwanted donkeys and horses at slaughterhouses. The government of Jalisco state imported a few male donkeys from a taller, stronger breed developed in Kentucky to revive interest in the animals for farmers.

Flores, an accountant, bought some land next to his family's home and opened the Burroland shelter in 2006. The place is not exactly scenic. There is no grass, and the donkeys wander among rusting 1940s-era cars scattered around the lot.

Visitors are given fake burro ears and tails to wear as they visit a small museum to learn about the animals' history. Children can pose for pictures with staff members dressed like the donkey from Shrek or Eeyore from Winnie the Pooh. Admission is free.

Flores also plans to sell a comic book he is writing about "Super Burro," a white donkey who works to prevent the extinction of burros in Latin America.

The shelter depends on donations from visitors, local companies and international groups such as Donkey Sanctuary in Britain. It costs about $15 a day to feed each burro, Flores says.

"I'd like to have more burros here, but it would be irresponsible because we don't have the money to keep and feed them," he says.

The animals have colorful histories. Roberto used to pull a junk collector's cart in Mexico City until he was hit by a bus and broke both front legs. Apache was rescued from a forest fire.

Flores says about 30 visitors show up on a good weekend. He wants to add a snack shop, expand the museum and build stables for all the burros.

"We want it to be a sustainable project and leave it as a legacy for Otumba and all of Mexico," he says.

A costumed staff member waves from the shelter's "burro-car."

Contributing: Chris Hawley in Mexico City