There are two types of window feeders: those attached to a window and those placed inside a windowsill. Feeders attached to a window are almost always attached to the glass via suction cups, but may be attached with Velcro. They are generally smaller than windowsill feeders and will typically fit any size or type of window.
Some windowsill feeders, called solarium feeders, protrude into the house through an open window; other windowsill feeders are secured outside a closed window. A solarium feeder rests in the windowsill and will ordinarily have adjustable side pieces that extend to the sides of the windowsill, closing off the open space much like the sides of a window air conditioner. Some windowsill feeders are secured on the outside of a window. This type of feeder allows the window to be completely closed.
A window bird feeder will allow you to observe birds up close, perhaps more closely than with non-window bird feeders or even bird blinds. Window bird feeders may also provide you with an economical solution to dealing with squirrel problem areas. If you live in such a squirrel problem area, simply try to find a window to which squirrels cannot jump such as a window with no branches close by. You can often install one or more window bird feeders for the same price as a "squirrel-proof" feeder.
Each type of window bird has its individual benefits as well. The benefits of using "on-window" feeders include the option of using multiple feeders on a given window and increased squirrel resistance. Squirrels are usually less likely to reach an "on-window" feeder than a windowsill feeder as they are nothing more than a variation of an open tray. Windowsill feeders, however, often have larger seed trays that will accommodate a larger number of birds and hold a much greater seed capacity than their "on-window" counterparts. Other features common to windowsill feeders include one-way mirrors that allow you to see the birds while they cannot see you and access to the seed tray from inside your house.
Window bird feeders that attach to windows are most frequently done so via suction cups, but sometimes by Velcro. Some people question the long term stability of suction cups; but if properly placed, suction cups should hold your window feeder indefinitely. When mounting your feeder, ensure that both the window and the inside of the suction cups are clean by rinsing them with warm water. Coating the inside of the suction cup(s) with a small amount petroleum jelly or cooking oil will further enhance the seal. After fixing the suction cups to a window, it may be necessary to squeeze out air bubbles by pressing your thumb from the center toward the outside; this should guarantee a clean, firm seal between the window and the suction cups.
Windowsill feeders mount in the sill of a window, either on the inside sill protruding into the house through an open window or on the outside sill of a closed window. A solarium feeder rests mounts on the inside sill of the window and will ordinarily have adjustable side pieces that extend to the sides of the windowsill, closing off the open space much like the sides of a window air conditioner. The feeder is then secured by closing the window on top of it. The other windowsill feeders are secured on the outside of a window by a tension pole (similar to a shower curtain rod) allowing the window to be completely closed.
After finding a window feeder that is compatible with your windows or windowsills, place the feeder in a window that faces an area that is attractive to the birds, is easily viewed from inside the house, and is easily filled either from inside or outside of the house. If you wish to attract specific species of birds, try to place your window bird feeder in a window that faces the habitat containing the most flowers, shrubs, and trees preferred by that species.
If the appearance of a solarium feeder or other window feeder raises a concern from an aesthetics standpoint, you may wish to place it in a window facing a backyard or in a window on a less conspicuous side of the house.
Depending on the type of window feeder used, a squirrel may or may not have easy access to the feeder. Feeders attached to a window are frequently smaller and more difficult for squirrels to access than windowsill feeders. Squirrels are usually unable to reach an "on-window" feeder. In general, windowsill feeders are nothing more than a variation of an open tray, which does not offer much squirrel protection in the event that a squirrel can jump to the window. If you have low hanging branches or structures providing squirrels access to your window, a windowsill feeder may not be the best choice.