Most of the migrants are Mexicans, often men in search of work with the pandemic easing and the U.S. economy set to boom. Apprehensions at the southern border totaled 382,000 from the beginning of the fiscal year in October through February, up 42% compared to the same period of 2019—a year that saw the highest number of apprehensions since 2007. In 2020, the influx of migrants plummeted due to the pandemic.

Single adults account for 82% of the apprehensions so far this fiscal year, according to U.S. Customs and Border Protection data. Some 60% of all single adults apprehended were Mexicans. Border patrol agents say the majority of single adults they catch are men, entering to look for work such as picking fruits and vegetables, roofing and dishwashing…

“The economy is going to reactivate very quickly in the U.S. They are already reopening, so it is a very good moment to be there,” Mr. Cruz, 41, said by telephone from a Catholic shelter in northern Mexico.