The shift also has to do with the increase in cellphone usage among migrants, Isacson said. He said migrants get information from "TikTok and WhatsApp and what you hear in shelters along the way, what other migrants tell you on the road."

"They're getting news in a way that you couldn't really get it before," he said.

Texas' share of arrests is the lowest it has been since October 2019, Isacson said. That's in part because the government of Mexico has upped enforcement against migrants traveling atop freight trains through the country up toward Texas.

Mexican officials have a harder time disrupting migration to Baja California, said a senior Customs and Border Protection official who asked for anonymity to speak freely.

That's because unlike many border towns across Texas, Tijuana is a prominent metropolitan area. Migrants use legitimate travel means to get there — some come by bus, others fly direct if Mexico doesn't require a visa for people from their country of origin.

Crossings tend to take place inland, where it's harder for Border Patrol to quickly respond.

The Department of Homeland Security — which oversees the border protection agency — is working to revoke visas or impose visa sanctions for charter transport companies involved in moving people toward the border, the official said.

The agency expects the trend to hold for weeks and is shifting personnel and other resources to the region in response, the official said. Some migrants are also being transferred to other regions that are seeing fewer arrivals and have more processing capacity.

The Biden administration recently allocated $45 million to California programs that help migrants who have crossed the southern border.

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