The number of able-bodied Americans entering the labor force has surged since last fall. But in a marked change from earlier in the recovery, more of them are finding jobs right away instead of just looking for work.

What’s going on? It’s hard to say for sure, but circumstantial evidence in the latest U.S. jobs report suggests many of these newly employed workers have found part-time work with mediocre pay.

The participation rate hit a two-year high of 63% in March, climbing from a 38-year low of 62.4% in September, the government said Friday. A person is considered part of the labor force if he finds or job or is actively searching for one.

Read: U.S. adds 215,000 new workers in March

The sharp rebound in labor-force participation after years of decline is a welcome turnabout, though economists are puzzled. Many had expected participation to remain low or fall even further as more baby boomers retire. Read: Economists react to solid March jobs report.

The strongest labor market in years helps explain part of the increase. Job openings are at a record high and companies in most industries are hiring.

But it doesn’t appear that companies are taking the first person they find and loading them up with work.

Consider so-called involuntary part-time workers. These are people who would prefer a full-time job or more hours if they were available. After hitting a post-recession low of 5.8 million in October, the number of people who can only get part-time work has bounced back up to 6.1 million, according to figures from the Labor Department’s household survey.

Hiring has been particularly strong in the past six months at retail stores and restaurants, where both pay and the number of hours employees work lags behind the national average.

The group with the biggest increase in participation since last fall, what’s more, are people without a high-school degree. They tend to be more heavily employed in retail or leisure and hospitality.

The number of hours the average person works each weak, meanwhile, has fallen several ticks since the beginning of the year. And wage growth has leveled off after touching a post-recession high several months ago.

Both are signs of a shift in hiring toward lower-paying jobs with fewer hours.

That’s not to say more people working is a bad thing, of course. The economy is clearly better off with 2 million more people working and making some money instead of sitting home and making none.

“The good news is that most of them have quickly found jobs,” speculated Steven Stanley, chief economist at Amherst Pierpont Securities. “The bad news is that most of those jobs, as you would expect, have been relatively low paying and many are only offering part-time hours.”