Homebuilders are snapping up land again after spending months shedding properties and suffering write-downs during the real estate bust.

The builders seek bargains in areas hit hardest by the real estate slump of the past three years, Bloomberg reports. That includes California, Florida, Arizona and Colorado.

“Like a shark has to keep swimming or it’ll die, it’s the same thing with builders,” Kathryn Boyce, regional director in Sacramento for Hanley Wood Market Intelligence, a real estate research company, tells Bloomberg.

“They have to keep building or they’ll die.”

The land purchases represent another sign that the real estate market is improving.

Home prices in 20 major cities rose 1.4 percent on average in June from May, according to the S&P/Case-Shiller index. That’s the largest gain in four years.

To be sure, prices in June were still down 15.4 percent from a year earlier. So the housing market certainly isn’t on easy street.

Robert Shiller, the Yale professor who created the index, has turned positive as a result of the latest data, but not completely.

“It has been an impressive turnaround. This is a huge, sudden, upward swing,” Shiller told CNBC. “I think it might represent a change in trend.”

Still, “I didn’t say we reached a bottom. I said that this is very suggestive of a major turning point,” he explained. “We’ve seen other corrections like this that were reversed,” and that could happen again.