Hollow tubes keep seed fairly clean and dry and, if they have metal feeding ports, may be somewhat squirrel resistant (though squirrels often chew through the end caps or the plastic tube itself). Depending on the size of the perches under the feeding ports, you may attract small birds such as sparrows, grosbeaks, chickadees, titmice, and finches while excluding larger species such as grackles and jays. Styles with perches above the feeding ports are designed for seed-eating birds that can feed hanging upside down, such as goldfinches and chickadees, while dissuading others. Depending on the size of the feeding ports, you can offer tiny nyjer seeds or larger seeds.
Unfortunately, the seed-containing tube on most tube feeders extends an inch or more below the bottom-most feeding ports. Seed that collects here may become a breeding ground for mold and bacteria. It’s best to block the bottom of the tube below the bottom feeding ports. Some tube feeders are huge, accommodating a dozen or more birds at a time. But these are best used only during times when many birds are using them. During periods when only a handful of birds use these feeders, use smaller models so the seed is used up fairly frequently.
When adding new seed to tube feeders, always empty the old seed out first.
TIP: Bird House Nature Company carries several styles of tube feeders. Aspects is known for their Quick-Clean removable base for easy cleaning.