Although many birds are carnivorous, meaning they eat meat, others eat only plants or plant parts. Most birds are omnivorous, meaning that they eat both plants and meat. Birds that eat plants (herbivores) can damage garden plants. Herbivores don't have teeth for grinding up the plants they eat, but use a part in their digestive system, called a crop, that contains stone-like features for grinding up vegetation. Most birds are omnivorous.
Parrots are herbivores that eat almost 30 different types of plants. Some common fruits eaten by wild parrots include plums and cherries. They also eat eucalyptus and carob leaves, in addition to flowers and nuts such as pecans. Interestingly, mother and father parrots are similar to humans in that they don't leave each other once they've mated, but become partners for life. Besides having a family, a good portion of a wild parrot's life involves searching for food.
Finches eat garden plants, in addition to meat and seeds. Some of the plants they eat include flowering grasses such as pampas grass. These birds are known for consuming garden plants such as artichokes, sunflowers, milk thistle, Michaelmas daisies, goldenrod, teasel and tickseed. Milk thistle and teasel, commonly grown as an ornamental plants, lure goldfinches, while greenfinches are attracted to tickseed. They're also carnivorous, eating insects.
Honeyeaters, which are a large diverse family of Australian birds, eat insects besides plants. Most of them feed on berries and the sap of plants. These birds are known for having a brush-tipped tongue that takes nectar from flowers. Different types of honeyeater species compete for plants in one area, with larger species such as Noisy Miners and Red Wattlebirds usually winning when grabbing flowers. On the other hand, smaller species such as Eastern Spinebills live with larger honeyeaters because they require less food and are able to sneak into flowering plants when enough leaves can hide them.
Canadian geese, which are notorious for invading gardens, are wild birds with a black head and neck. They're mainly herbivores, feeding on various plants and aquatic vegetation. Most of their diet consists of wasted grain in plowed fields during winter and while migrating. They typically enter a butterfly garden from a pond, and graze on ornamental flowers, preferring young tender plants. The Wild Flower.org website suggests enclosing new plants in wire netting to protect them from these predators. They're also unwelcome guests because they drop sizable amounts of manure on lawns and gardens.