McALLEN - On a recent evening near the banks of the Rio Grande, a group of five Guatemalan immigrants, among them two girls, ages 8 and 10 without a parent or guardian by their side, turned themselves over to U.S. Border Patrol agents.

It is a familiar scene to law enforcement agencies in South Texas that witnessed nearly 50,000 unaccompanied children and families, mostly from Central America, illegally streaming across the border here last year.

While far fewer immigrants have been detained in recent months than during the same period a year ago, thousands are still crossing the Rio Grande illegally, and border agents are bracing for thousands more in the months ahead.

"It's a guessing game," said Monique R. Grame, deputy patrol agent in charge of the McAllen station. "Come early June, we'll have a pretty good sense of how busy it'll be."

Numbers on the rise

By this time last year, Border Patrol was already seeing a spike in immigration and the influx eventually "crashed the system," Grame said. Even as the number of unaccompanied minors caught along the Southwest border is down 45 percent from last year and detained families down 30 percent, the incoming tide remains significant and once again on the rise.

Already, 15,647 minors and 13,911 families have been detained since the beginning of the fiscal year in October, along the whole Southwest border, most of them in Rio Grande Valley. With the historically busy April, May and summer months ahead, it is conceivable that apprehensions this year will surpass all but the unprecedented surge of 2014.

Border agencies say they are better equipped to manage another surge, with more space for families at detention facilities in Dilley and Karnes, and up to 7,300 beds in facilities across the country for unaccompanied minors, who must be transferred within 72 hours to the Office of Refugee Resettlement, part of the federal Health and Human Services Department.

Now, there are more than 3,000 Border Patrol agents stationed in the Rio Grande Valley who regularly patrol alongside state agencies deployed to the border last summer, part of the multimillion-dollar border surge started by former Texas Gov. Rick Perry.

Perry activated up to 1,000 National Guard troops to the border in July, and a few hundred remain in the Valley. He also sent Department of Public Safety troopers and game wardens.

Other measures to slow illegal immigration, such as an international media campaign and sped-up deportation hearings, appear to have eased the shear volume of immigrants, too.

Violence worsens

Meanwhile, security remains largely unchanged in Central America, while it has arguably worsened in El Salvador, with 481 homicides in March, making it the deadliest month in a decade.

As a police officer in El Salvador, Julio Vergara, 33, knew he was a target of gang violence, but when they came after his son, it was more than he could bare. Seven months ago, his wife and 12-year-old son crossed the border in the Rio Grande Valley, and last month Vergara and their 13-year-old son followed. His immigration hearing is set for later this month in Houston.

"The gangs are out of control in my country," Vergara said. "Gang leaders put out an order to kill police. … In December they killed a friend in front of his home."

Vergara said he took out an $8,000 bank loan to pay smugglers to take him and his son through Mexico, where it has become progressively more difficult for migrants.

Under pressure from the United States to stem illegal immigration at its shared border, Mexico last fall began pulling migrants off of northbound trains, setting up road checkpoints and raiding hotels.

In January and February, Mexican immigration officials cracked down on immigrants like never before, deporting more than 25,000 Central Americans compared with 12,800 the year before, and nearly 3,300 minors, up from 1,605 in same time period, according to the Washington Office on Latin America, an advocacy group.

Instead of deterring immigration, however, some observers and human rights groups say ratcheted-up enforcement measures on Mexico's southern border are pushing migrants away from established support networks and further underground.

"There are some real concerns that Mexican authorities aren't properly screening these migrants to make sure that refugees and victims of human trafficking or other serious crimes get the protection they need," according to Clay Boggs, program officer for WOLA.

Earlier this year, the Obama administration requested $1 billion from Congress for Central America, largely in response to the wave of more than 51,000 children from Honduras, Guatemala and El Salvador who last year fled rampant violence and crushing poverty at home.

Mother and son

Just before sunset one recent evening border agents handed out water bottles to a group of four Honduran immigrants. A young woman who moments before waded through the shallow Rio Grande sat quietly with her 2-year-old son.

"Where is his father?" one agent inquired as the Hondurans climbed into a van filled with other apprehended immigrants heading to the McAllen Border Patrol station.

"He doesn't have one," she said, her eyes welling with tears.