(An excerpt from Gaia’s Garden)
Many gardeners don’t welcome birds into the garden or orchard with unambiguously open arms. Birds can decimate a berry crop, peck holes in fruit, and scratch up small seedlings. Often these problems arise because good bird habitat is lacking, and the birds are reduced to making do with what’s available (in other words, your plants). I’d argue that in a well-designed, balanced landscape, birds do far more good than harm. They are supreme insect predators, attacking both leaf-munching caterpillars and flying bugs. Many birds eat seeds, reducing the number of weeds. In return for this food, they leave small gifts of rich manure. Individual bird droppings may not amount to much, but when a gardener concentrates manure by hanging a feeder or by some other tactic, plenty of fertilizer can accumulate. Birds also scratch the soil, simultaneously tilling the ground, removing insects and weed seeds, and uprooting weed seedlings. Some small birds are good pollinators. And then there is the simple joy that birds bring, with their bright plumage, burbling song, nest-building and family-raising, and their endlessly varied behavior as they hunt, court, stake out turf, and socialize. A yard without birds seems a sterile place.
To see how to attract birds to the landscape and to benefit from them, let’s once again take the ecological view. What kind of habitat gives birds all that they need? Once we’ve answered that, we can see how to blend bird habitat, and all the gifts birds offer, into the garden.
Imagine a backyard of bare ground. A little bare earth is useful for birds, who will take dust baths in dry soil to subdue mites and other parasites. Birds also eat grit to aid digestion. But without shelter from predators and the elements, no bird can live here. Occasional visitors might come to pluck worms or ground-dwelling insects from this empty place, but not to stay.
Allow a low ground cover to carpet the soil, and the friendly microclimate and greenery will attract several types of insects. Now ground-nesting birds such as meadowlarks and certain sparrows may appear to feed on bugs and seeds. These two types of food foster diversity in bird residents: insect-eating birds have long, slender beaks to pluck insects from foliage, while the bills of seed-eaters are short and thick to crack tough seeds. As the environment grows more complex, bird anatomy and behavior diversify as well. The implication: More species of birds can coexist in complex habitats than in simple ones.
Bring in a little more plant diversity: tall grasses. Thick, high grass offers birds protection from predators, but also hampers bird flight. Birds that live in tall grass will be different from ground-nesters. They have short wings and tails to nimbly maneuver through the grass, hopping rather than flying.
This is still a fairly impoverished home. Let’s add some shrubs, which foster diversity in several ways. One is by moving firmly into the third dimension, height. This provides perches for birds, where they can sit and watch for prey rather than hopping about in continuous search. Sit-and-wait hunting conserves energy, leaving more for breeding and social behavior. Perches also encourage flying, so the wings and tails of shrub-dwelling birds are bigger than the sawed-off stubs of grass residents. Also, birds that hunt bugs on the wing have broader bills to raise the odds of nailing insects with each swoop. Nests, now off the ground, are safer, cooler, and drier, so more nestlings survive.
Perching birds are superb seed dispersers and can bolster plant diversity on their own. Researchers found that by providing perches in a field, the number and variety of seeds brought by birds skyrocketed. If we offer the birds a few shrubs for perching, they’ll introduce many new plant varieties on their own. This in turn will attract new insects, which will bring more new birds, who will ferry in more seeds, and up and up the cycle builds.
Another boost to diversity offered by shrubs is from woody tissue. Grass and herbs have soft stems and foliage, thus insects can munch them with ease. But the woody stems of shrubs will thwart a soft-mouthed bug. Woody stems offer a whole new niche, welcoming insects with tough jaws or piercing mouthparts. Thus a shrub-filled landscape is home to yet more species of insects, and that means more types of birds to eat them.
Within the shrubby canopy, small birds are protected from predators. These birds can hop from twig to twig, snapping up insects. They’ll have sharp, pointed beaks to poke into small places in search of food. Here come some more new species.
The move to the third dimension really boosts diversity, opening up many new opportunities for food sources and consumers of that food. As the habitat diversifies, more and more birds find niches, and create more variety in turn. Also, a combination of herbs and shrubs will nurture not only the birds dependent on each, but new species that colonize the edge between the two habitats.
Selected Excerpts from Gaia’s Garden: