The Border Patrol nabbed more than 15,000 illegal immigrants traveling as families on the southwest border in November — a massive increase that marks the worst November on record and the second worst overall, according to statistics released Thursday.

The number of children traveling without parents also ticked up, topping 7,000 for the month, but it’s the surge of families that is straining the Border Patrol and testing the Obama administration’s resolve.

Combined, the children and families fleeing Central America for the U.S. have reshaped the challenges of the illegal migration problem, sending overall illegal immigration numbers back to levels not seen in years. The 47,214 illegal border crossings reported in November is 44 percent higher than in 2015 and marks the worst November in years.

The families and children are trying new methods, including showing up and demanding entry to the U.S. Officers at the legal ports of entry reported a 226 percent spike in children they encountered in October and November, compared with the same two months in 2015.

Obama officials blame conditions in Central America, saying poverty and violence in El Salvador, Honduras and Guatemala are forcing people to make the trip north.

But the Border Patrol’s chief told Congress that U.S. policy is inviting the surge because migrants, coached by the smugglers they are paying, have learned to game the system.

The worst month for children and families was June 2014, the peak of the previous surge. But migration is cyclical, and the fact that this year had the worst November on record suggests that fiscal year 2017, which began in October, is poised to set more records for families.

U.S. Customs and Border Protection, the agency that oversees the border, said the surge goes beyond Central Americans.

Haitians displaced by natural disasters, who have been living in Brazil for years, also have been making their way north. Authorities are seeing an increase in the number of Cubans, too, the agency said.