Americans’ love of pickup trucks, the lifeblood of Detroit auto makers and once the darling of U.S. consumers, marked a 31-year low in April.

Against a backdrop of sluggish housing starts, high unemployment and skyrocketing pump prices – key historical barometers for the segment – full-size and small pickups accounted for 11.8% of total light-vehicle deliveries in the month

It is the segment’s lowest market share in the Ward’s database, which dates back to 1980. At their peak in July 2005, pickups accounted for 22.9% of U.S. LV sales.

The share shortfall occurs as sales climb. Through the first four months of 2011, pickup deliveries were tracking 17.9% ahead of like-2010. However, total U.S. light-vehicle sales were pacing 19.4% ahead of prior-year, according to Ward’s.

The downturn for pickups is the latest notable shift in U.S. consumer preference, which has seen light-truck demand dwindle in favor of cars. Light trucks outsold cars in 2010, but through April their lead slipped to a slim 5,000-unit advantage.

“In Texas, the biggest truck market in the U.S., our volume typically was 50% F-Series sales,” says Randall Reed, owner of five Ford dealerships in the Lone Star State.

“But that has come down since the Fiesta and the Fusion,” Reed tells Ward’s, referring to the launches of the Blue Oval’s B-segment and midsize-car entries. Factor in the new-for-’12 Focus C-car, and “we’re going to balance out and be selling more cars than ever in our history,” he adds.

Historically, pickup share has run second to the Middle Car segment, as defined byWard’s. In 1980, pickups accounted for 14.7% of the U.S. light-vehicle market, while the Middle Car segment commanded nearly three times that amount, or 39.8%.

By 2005, the two segments were running bumper-to-bumper, with pickups controlling 18.77% of the market compared with the Middle Car segment’s 18.79%.

Through April, pickups accounted for 12.6% of U.S. light-vehicle sales, while the Middle Car segment made up a whopping 20.8%.