If you haven't purchased bird seed since spring, you may experience sticker shock when you return to your favorite seed supplier.

I feed birds all year, so I've felt the pinch over the last 12 months. The price of black-oil sunflower seed has more than doubled since last fall. The best price I've found locally last week has been $24.95 for 50 pounds.

There are two reasons for the dramatic price increase. First, the price of gasoline and diesel fuel has significantly increased transportation costs. Second, many sunflower growers have switched to crops that produce biofuels; that means fewer acres planted in sunflowers. Consequently, the supply of sunflower is down, and the price is up.

Despite the price increase, sunflower seeds remain the single best food for seed-eating wild birds. Black-oil sunflower is appealing because it has high oil (energy) content, and its shells are thin and easy to crack.

Striped sunflower seed is also great, but its heavier shell makes it more difficult to crack for smaller birds. It's a favorite of cardinals, grosbeaks and blue jays. Hulled sunflower seeds are more expensive because the hulls have been mechanically removed. But there is no mess and no waste -- every bit of each kernel is eaten. Despite the higher price, I think sunflower kernels are a better value than in-shell seeds, particularly when transportation costs are considered.

I'll conclude with a warning. Bird feeders can be "bear magnets," so Mark Ternent, bear biologist for the Pennsylvania Game Commission, offers advice to anyone who lives in bear country.

• Restrict the bird feeding season to when bears hibernate: late November through late March

• Avoid foods such as table scraps, sunflower seeds and suet that attract bears.

• If you stock feeders while bears are active, take them inside at night or suspend them from high cross wires.

• If bears visit a feeding station, remove the feeders for two weeks.