When it comes to keeping squirrels out of your feeder, reviewers like the Droll Yankee and Brome tube feeders discussed earlier. However, they don't hold that much bird seed (about 3 quarts for most models). Hopper feeders, which come in many styles, are often larger, so you'll have to refill it less often.
Dummies.com says hopper feeders are "big and bird-friendly," and attract a wide assortment of birds, even big or shy ones. The Mandarin (*Est. $60) and the Sky Café by Arundale (*Est. $60) are domed hopper feeders made of transparent, recycled Plexiglas. They look nearly identical, but the Sky Café has a circular platform around its base, which allows cardinals to perch, while the Mandarin omits the base but has several seed ports and stick-like perches more suitable to smaller songbirds. The platform at the bottom of the Sky Café has standing room for 10 or more birds.
Bill Adler, Jr., author of "Outwitting Squirrels," gives the Mandarin his highest overall score. Its roof has a unique shape somewhat like witch's hat or an upside-down funnel, with a steep slope that sends squirrels sliding to the ground. With a wide opening (over 6 inches), Adler says these feeders are easy to fill, minimizing spilled seed. Each holds more than 5 quarts of seed. Just be careful not to drop the feeder. A few comments posted on Amazon.com by otherwise pleased customers indicate the plastic can shatter.
One squirrel-proof feeder that works but is expensive and battery-dependent, according to reviews, is Wild Bill's Squirrel-Free Feeder (*Est. $125). This domed hopper feeder uses a mild static shock to train squirrels to keep away. It doesn't harm birds, but it relies on a 9-volt battery that has to be replaced, and the feeder is guaranteed for only one year. There are several straight perches and a circular aluminum tray to catch seeds and provide additional space for birds. This feeder attracts a wide variety of birds. However, some owners aren't crazy about using an electric shock to repel squirrels. This model has a particularly large capacity (up to 20 pounds of seed).
A budget alternative to a squirrel-proof feeder is to add a baffle (which you can make or buy) to a regular feeder. A baffle is a barrier shaped like an upside-down bowl. On a hanging feeder it is placed above the feeder. On a pole-mounted feeder it is placed underneath. According to the Cornell Lab of Ornithology, people have constructed homemade versions from two-liter soda bottles, plastic salad bowls, and even old vinyl records. This is an inexpensive way to adapt a bird feeder of almost any size.
Another alternative is to serve safflower seeds, a kind of seed that experts say cardinals love but squirrels don't like.