MADISON, Wis. - Classroom desks and office cubicles stand empty. Hunters in blaze orange stand out like drops of bright paint against brown fields. Pub parking lots are crowded with pickup trucks draped with deer carcasses.

This is Wisconsin's gun deer season, a tradition as engrained in this rugged state's identity as beer, brats and cheese. But as the years slide by, fewer people seem to care.

Hunting's popularity has waned across much of the country as housing tracts replace forests, aging hunters hang up their guns and kids plop down in front of Facebook rather than venture outside.

The falloff could have far-reaching consequences, hunting enthusiasts say. Fewer hunters mean less revenue for a multibillion-dollar industry and government conservation efforts.

"As paradoxical as it may seem, if hunting were to disappear, a large amount of the funding that goes to restore all sorts of wildlife habitat, game and nongame species alike, would disappear," said Steve Sanetti, National Shooting Sports Foundation president.

Hunting generates billions in retail sales and pumps hundreds of millions of dollars into government conservation efforts annually through license sales and federal taxes on firearms and ammunition sales.

But fewer hunters return to the sport each year. The U.S. Fish and Wildlife Service estimates 33 states experienced declines in hunting-license sales over the last two decades.

Suburban sprawl has consumed prime hunting land, forcing many hunters to choose between driving for hours to get to the woods or staying home.

Gerald Feaser, a Pennsylvania Game Commission spokesman, said his state's urban footprint has nearly doubled since the early 1980s.

"Whole farms turned into housing developments or shopping malls," he said. "Once that land is lost, you can't get it back."

In Pennsylvania, license sales have dipped 20 percent over the last two decades.

The state's game commission has trimmed spending by about a million dollars in the last two years, cutting back efforts to repopulate pheasants, leaving 30 positions unfilled and asking employees to repair their own vehicles, Feaser said.

To stave off the losses, states and outdoors groups have stepped up efforts to retain and recruit hunters. The U.S. Sportsmen's Alliance, the National Shooting Sports Foundation and National Wild Turkey Federation launched the program Families Afield in 2005 that calls for states to scale back youth hunting regulations. Thirty states have since reduced or eliminated minimum hunting ages, NSSF spokesman Bill Brassard Jr. said.