WASHINGTON -- Police seizures of drop houses, where smugglers "stash" undocumented aliens en route to other parts of the country, have plummeted in Arizona this year, continuing a trend that began in 2008.
Through July 17, the Arizona Department of Public Safety's Illegal Immigration Prevention and Apprehension Co-Op Teams (IIMPACT) reported seizing only one drop house. That compares to 18 last year and 49 in 2008, a year after the task force began operation.
While not as steep as the IIMPACT drop, federal officials also reported a decline in drop houses uncovered in the Phoenix area.
U.S. Immigration and Customs Enforcement said it had found 30 drop houses in the area by June 27. That would put it on pace for about 40 by Sept. 30, the end of the fiscal year, compared to 51 in fiscal 2011 and 186 in 2008.
Authorities said tougher enforcement has pushed "coyotes" -- smugglers who bring undocumented aliens into the country -- into passing through Arizona toward other states.
"We made it hard for them to operate," said Bart Graves, a spokesman for DPS.
Others said that while increased policing has played a role, there are other factors involved, including everything from a stagnant U.S. economy to higher prices charged by coyotes.
"There are a number of indications in the data we have that fewer people are trying to cross the border into the U.S.," said Jeffrey Passel, a demographer at the Pew Hispanic Center. That translates into fewer undocumented workers who are trying to sneak in, he said.
Authorities said coyotes use drop houses as stopping points on this side of the border while they transport undocumented aliens farther into the country. The houses are also where the smugglers sometimes hold illegal immigrants hostage to extort more money from them, police said.
An ICE official attributed the decline in the number of drop houses uncovered to "the unprecedented resources [ICE] has deployed to the Southwest border." The success was also attributed to expanded partnerships with federal, state, tribal and local partners, and help from the government of Mexico.
ICE is part of the IIMPACT team with state police.
The decrease in drop houses comes as apprehensions of illegal immigrants have also dropped. Pew attributes that drop both to the collapse of the U.S. housing market, and the construction jobs that came with it, and to the increased law enforcement presence on the border.
"In spite of (and perhaps because of) increases in the number of U.S. Border Patrol agents, apprehensions of Mexicans trying to cross the border illegally have plummeted in recent years -- from more than 1 million in 2005 to 286,000 in 2011," a Pew study said.
Passel also said that the cost of hiring a coyote has risen. When that's combined with fewer employment opportunities on the U.S. side and the effects of heightened security -- a higher chance of getting caught and a physically harder trip as traffickers move toward remote, rural routes -- border crossings drop, he said.
The Pew study also cites "a rise in deportations, the growing dangers associated with illegal border crossings, the long-term decline in Mexico's birth rates and broader economic conditions in Mexico," as factors for the decline in immigration.
ICE said apprehension is a key indicator of the number of illegal immigrants. But Passel said that while the number of people caught trying to sneak into the country is "not a direct measure of flow" of illegal immigrants, "they do seem correlated."