The reason Chihuahuas and their many mixes are among the dogs most often found in animal shelters, animal-care workers say, lies somewhere in the intersection of geography, pop culture and immigrant tastes. Breeders play a role, too: Some do not realize that female Chihuahuas are so small that they often need a cesarean section, an expensive procedure that can wipe out potential profits and prompt people to abandon the dogs, said Lynnie Bunten, breed rescue chairwoman at the Chihuahua Club of America.

Image A stray Chihuahua is placed in a truck kennel after wandering into an elementary school in Phoenix. Credit... Samantha Sais for The New York Times

On average, purebred puppies sell for $300 or $400, but Chihuahuas are a lot more common in states bordering Mexico, Ms. Bunten said. Shelters in San Antonio, where she lives, are “brimming with Chihuahuas,” and in California, several cities have passed ordinances requiring that Chihuahuas be spayed or neutered in an effort to legislate population control.

The dogs are also status symbols of sorts: Chihuahuas have served as the Taco Bell mascot (“Drop the chalupa!”), Disney movie stars (think “Beverly Hills Chihuahua”) and fashion accessories for the likes of Paris Hilton and Britney Spears, not to mention Elle Woods in the movie “Legally Blonde.” When mixed with other breeds, they go by cutesy names like Chugs (Chihuahuas and pugs), Chiweenies (Chihuahuas and dachshunds) and Chi Pins (Chihuahuas and miniature pinschers).

“Young women put them in their purses to make an impression, kind of like the big macho guys get pit bulls to look tough,” Ms. Bunten said.

A study published by The Journal of the American Veterinary Medical Association in 2010 found that Hispanics were more likely to own pets that had not been spayed or neutered than were people of other races and ethnicities, a factor that seems to be contributing to the overabundance of Chihuahuas. Hollister, Calif., where roughly 66 percent of residents are Latino, has seen a “significant drop” in the number of Chihuahuas since passing an ordinance in 2010 mandating that the dogs be spayed or neutered, said Julie Carreiro, supervisor of the Hollister Police Animal Care and Services.

Arizona’s Maricopa County, where the shelters take in more animals than any county besides Los Angeles County, is discussing a partnership with one of Phoenix’s most popular Spanish-language radio stations, La Campesina, to spread the message that sterilizing dogs “is part of the responsibility of owning a pet,” said Melissa Gable, spokeswoman for the county’s Animal Care and Control.