Denver’s housing rebound is in full swing, but sellers are acting as though they didn’t get invitations to the party.

“The question each and every day is: Where are the sellers?” said Gary Bauer, an independent real estate research analyst.

At the end of April,metro Denver had just shy of 7,000 pre-owned homes available for sale, a third fewer than a year earlier and less than half the 15,000 to 20,000 homes that Bauer said would represent a normal market.

“I can’t figure out why people aren’t listing,” said Brenda Yates, a broker associate with Keller Williams DTC.

Yates and her husband plan to put three properties on the market, after finally seeing enough appreciation to make it worthwhile, and they don’t expect it will take long for them to sell.

The median price of homes sold in metro Denver last month rose to $280,000, up from $268,200 in March. The latestStandard & Poor’s/Case-Shiller Home Price indexreports 14 straight months of price increases in Denver, with prices up nearly 10 percent year-over-year as of February.

Scarcity is triggering bidding wars and causing homes to move quickly, often on the first day, brokers report. The median time a new listing in April remained available before going under contract was four days, reports Jim Smith, owner of Golden Real Estate.