Most backyard birds are opportunistic feeders. While every bird species has its own unique food requirements, the type of food they eat often changes with the environment, the seasons, and the age of the bird. For example, finches are frequent visitors at backyard seed feeders, but they also eat a few buds in spring, insects in summer, and berries in fall. And many species of birds that typically gorge on insects switch to a diet rich in berries when migrating in fall.
Growing a diversity of food-bearing plants will help ensure an all-you-can-eat bird buffet by providing nourishing nuts, seeds, fruits, berries, buds, and nectar (for hummingbirds and orioles) throughout the year. Red mulberry and sassafras are good berry sources in spring and summer, viburnums offer berry sustenance in summer and fall, and the fruit of hollies and hawthorns ripen in fall and, in some species, last into early spring. And because an organic garden is also home to a variety of insects and caterpillars, there's always a ready food source for robins, swallows, and other birds that rely on insects as part or most of their diet.
As essential as plant diversity is to attracting a greater number of bird species, offering supplementary food via a bird feeder can add that extra element of enticement—especially in winter when seeds, insects, and other foods are in short supply. You can cater to different species of birds by offering seeds they like, such as nyjer seed for finches. Or fill your feeders with black-oil sunflower seeds, which appeal to the widest variety of bird species. This bird-feeding strategy also eliminates the waste that often comes with birdseed mixes. If you do use a birdseed mix, opt for one that contains mostly black-oil sunflower seeds mixed with millet and cracked corn. Feeding birds helps bridge the gap when winter food sources dwindle, but designing a bird-friendly landscape is better for bird populations in the long run because it provides not just food but also a place to live and breed.