Feeding on the Wing
One of the pleasures of the Sonoma State University campus is a colony of cliff swallows that nest high on the walls of Salazar Hall, adjacent to the main quad. Watching their graceful flight is always a welcome diversion from the task at hand, and I look forward to their return each spring. Cliff swallows, along with barn swallows and phoebes, have adapted well to the intrusion of humankind, who provide convenient nesting sites on buildings, bridges, and under the eaves of houses. And what a fortuitous thing that is! Barn swallows wheeling and swooping above my garden are always a delight, not only because their aerial acrobatics are entertaining, but also because mosquitoes are one of their favorite foods.
Varied Diets and Feeding Styles
The birds discussed here catch insects on the wing; birds that catch their prey by gleaning it from foliage, bark, or ground, were discussed in a previous article (January 2010). Some birds, such as orioles, are primarily gleaners, but will go after a flying insect when the opportunity presents itself. True aerial insectivores, such as swallows, hunt on the move, often swooping back and forth through swarms of insects to catch their prey. Nighthawks and nightjars (neither are raptors) are aerial insectivores that hunt nocturnal insects. Nighthawks are also well adapted to disturbed habitat, and thrive in urban environments, where they can be found nesting on flat rooftops. Swifts are perhaps the most aerial insectivores of all, spending most of their lives, and carrying out most of their activities, on the wing. Other birds are known for hawking; from a comfortable perch, they scan the vicinity for food and sally forth when prey is spotted. Western bluebirds, black phoebes, and a few others feed from perches close to the ground.
Most aerial-hunting insectivorous birds are fairly indiscriminate in their choice of insects, but may refuse certain arthropods, such as spiders. Swifts search out lipid-rich insects such as swarms of flying termites and ants. Swallows feast on mosquitoes, and several kinds of owls eat moths and other large flying insects. Flycatchers pursue many species of insects, especially the diptera (flies) for which they are named, but also bees, wasps, beetles, and grasshoppers. Some flycatchers, such as phoebes, often catch their prey near the ground, or even snatch it off the ground, but quickly take flight again. Warblers, and cedar waxwings sometimes catch insects on the wing. Gleaners sometimes feed arthropods to their nestlings, but may feed primarily on grain or foliage as adults; aerial insectivores such as swifts feed on insects in all stages of life.
Welcoming Birds to the Garden
Attracting birds to the garden is the perfect way to begin learning bird species. Encouraging garden birds is yet another reason to avoid using pesticides; insectivorous birds may be easily poisoned when eating insects that have been exposed to pesticides. Why not eliminate pesticides, and encourage insectivorous birds to keep insects in check? Keep birds in mind when designing and planting gardens, and don’t be surprised when new bird species arrive as time passes and the garden matures. Proximity to wilderness and permanent water increases the number of species that are likely to visit gardens, but even urban gardens may be visited by a surprising number of species.
Information on planting habitats for birds usually focuses on providing food in the form of fruit, seeds, and foliage, cover for nesting, and plantings in layers and “ladders” to allow safe passage through the garden. Planting to attract insects that birds eat is frequently overlooked when planning a bird garden, but even non-insectivorous nesting birds need an abundant supply of insects for nestlings. Willows, for example, are habitat for numerous insects eaten by birds, as are oaks. Many flowering perennials support butterfly larvae and bees, wasps, and flies that insectivores relish. Native shrubs often provide an important source of insects, especially those that bloom early in spring, such as Ceanothus, or late in the season, such as coyote brush (Baccharis pilularis). Providing water is essential; birdbaths should be shallow and provide secure footing. Positioning a birdbath where birds will feel safe can take a bit of experimentation. Nearby branches for perching, and a clear view to safety are the minimum requirements for most birds to comfortably use a birdbath.
Building nesting boxes and platforms can encourage birds to establish themselves in even a small garden, provided there is suitable habitat. Each species has specific requirements for nesting; some birds need a fully enclosed box with an entry of exacting diameter, installed with a specific exposure, and at minimum height. Other birds are satisfied with a simple platform tucked under an eave; black phoebes can often be found nesting in such situations. Barn swallows, as their name indicates, are frequently found in old barns and other large buildings in rural areas.
My friends will tell you that the plants in my garden have been chosen to attract insects. For the most part, they are correct, but I have planted many species of fruits, berries, and bunch grasses for birds. There is no doubt, however, that plants I have included to attract insects also attract insectivorous birds. As I watch the activity in the garden, I am sometimes led to think that my garden really is for the birds!
In a Nutshell
Most of the birds listed here are collectively known as perching birds or songbirds—passerines (Order: Passeriformes), which includes over half of all bird species. Nighthawks and nightjars are in the Order: Caprimulgiformes. Swifts are in the Order: Apodiformes.
Birds discussed here belong to the following families: Caprimulgidae (nighthawks and nightjars), Hirundinidae (swallows), Laniidae (shrikes), Apodidae (swifts), Turdidae (western bluebird and all thrushes), Tyrannidae (phoebes and flycatchers), Bombycillidae (waxwings), and Parulidae (warblers). This list is not inclusive of all common aerial-hunting, insect-eating birds.
Common Garden Species:
Most of the species discussed are common in gardens. Nightjars and nighthawks may be less common than some other aerial insectivores.
Many common garden birds have a wide distribution along the Pacific Coast; some may be only seasonal visitors. Some common birds such as swallows have a patchy distribution.
All birds lay eggs. Most birds mate and produce young in the spring, when food is abundant; some may produce more than one brood. Even adult birds that are not insectivorous will often feed their young high-protein insects.
Winged and feathered with two feet! Often have distinctive markings. Many insectivorous birds are quite small and continually active, as they search for food.
Varies widely: while most passerines do not live more than one or two years in the wild, birds that survive their first year may live for several years. Birds in other orders may have longer lives. Larger birds often live longer than small birds.
Birds may be completely insectivorous, eat a widely varied diet, or eat insects only occasionally. While some birds are indiscriminate in choice of arthropods, others specialize on certain insect orders.
Thorny plants (for nesting), fruiting and seed-bearing plants, conifers and deciduous trees all offer valuable resources for birds. Many plants are hosts for insects favored by birds. Choose suitable plants for locally resident birds.
Swallows and other nesting birds may create messes on buildings and on pavement below their nests.
Cliff swallows practice brood parasitism: females sometimes lay eggs in other females’ nests. Recently, they have been found to carry their eggs from their own nest to another’s nest. Shrikes impale their prey, such as grasshoppers, on sharp thorns or, sometimes, barbed wire.
Sources: Birds are natural visitors in most gardens.
The Sibley Guide to Bird Life & Behavior, National Audubon Society, 2001: an excellent companion to bird guides, full of information on natural history.
Peterson Field Guide to Birds of North America, Roger Tory Peterson, 2008: easy to use guide with good distribution maps.
Two sites from the Cornell Lab of Ornithology are useful for any birder: http://www.allaboutbirds.org/guide/search and http://www.birds.cornell.edu/nestinginfo/nestboxref/construct.
The local chapter of the Audubon Society is a tremendous resource for birders: www.audubon.org.