Biology Comics

Suburbs are for the Birds!

In an earlier Comic I mentioned the local cowbirds terrorized by sharpshinned hawks and merlins. The cowbirds lay their eggs in the nests of other birds and let them raise their young; the growing cowbirds push the competing young out of the nest. Over the last century cowbirds have spread from the plains and prairies east into the artificial human prairie that has replaced the eastern forest in North America and (along with midsized predators like raccoons, opossums, house cats and skunks) have helped reduce songbirds populations by 50% or more (habitat change and industrial pollution also helped). When I moved to the Adirondacks in 1972 the spring sighting of a male cowbird gurgling from the top of our bare apple tree, the glossy black singer perched above his two dove gray companions, made me smile. The cowbird was a common bird in central New York, where I grew up, but (like the raven or the turkey vulture) uncommon in the Adirondacks in the 1950s.

While doing his laundry in a nearby village a friend watched a merlin (a fierce little falcon the size of a robin) harassing the starlings that nested in the eves of the laundromat. Merlins were extremely uncommon 40-50 years ago but over the last decade have been on a roll.

Until fairly recently it was legal to shoot hawks (many of them ate domestic chickens and ducks) and in the early twentieth century thousands were shot each fall as they slid south on air currents above Appalachian ridges, or cruised along Atlantic beaches. Walkers in the woods shot them. Pennsylvania had a $5 bounty on goshawks in the 1930s (not a small sum at the time) when Hawk Mountain Sanctuary was established. Bird books from the early twentieth century debated which raptors should be eliminated: usually the verdict fell on the bird killers, the three short winged hunters of the forest, the sharpshin, the Cooper’s hawk, the goshawk, birds of similar form and abilities in different sizes. The merlin’s rarity made it unimportant. The writers of the books were ornithologists (they favored more songbirds). The story is the same as for mountain lions and wolves (to which many hawks were compared): shot to save the deer.

These books have tales from when hawks were more abundant. Goshawks, the largest of the accepters (and thus the least common, but commonly seen) would strike a rabbit or a hen with such force that the animal’s side would be torn off. When shot at while striking a hen, a goshawk would attack the man with the gun. In thick cover they would bound under trees after rabbits they had missed. Anything that flew or ran was fair game. One battle between a goshawk and a barred owl ended with both birds dead, the owl bleeding to death, the goshawk beheaded.

Large hunters are used to getting their way. They don’t like to be told what to do. Their fierceness helps them survive.

Hawks also suffered from eggshell thinning during the age of DDT (1945-1972 in the United States; approximately the economic life of the manufacturing facility). DDT interfered with calcium metabolism in birds; the result was eggshells that broke under the weight of a brooding bird. Not only hawks suffered, smaller birds did also, but being at the top of long food chains that accumulated the chemical, hawks suffered the most. Peregrine falcons more or less disappeared from Great Britain and the eastern United States. Goshawks, which eat gamebirds and small mammals, which eat leaves, berries and grass (thus situated at the end of shorter foodchains), suffered less.

Lately other chemicals, including other industrial chlorinated hydrocarbons that act as hormone mimics, like DDT, and heavy metals like mercury, a neurotoxin released by burning coal, have become problems for some birds (gulls, cormorants, thrushes); but some raptors seem to be increasing.

Not only hawks were more abundant. Flocks of black billed cuckoos followed infestations of tent caterpillars and would clear small orchards of their nests in a day. One of the common names for the rose breasted grosbeak was potato bug bird; but I have never seen grosbeaks eating potato bugs (or in numbers that could eat enough to help). Cuckoos are now rather uncommon and the silken nests of tent caterpillars on roadside trees (most birds won’t eat the hairy adults) go unmolested.


Such stories make one suspect that populations of North American breeding birds are really down 90-95% from the time of European settlement.

Conservationists who want to restore large animals speak of the three Cs: cores, corridors, carnivores. Cores are ecosystems restored as much as possible to their wild state (thus without people in the developed world). Corridors connect cores, turning separate populations of plants and animals into metapopulations. Carnivores influence the growth of plants and the abundance and types of animals and so are necessary for the health of cores.

This influence of carnivores happens on all size levels, from microbes to moose. Large carnivores influence forest succession by eating large herbivores like deer and moose, which through their feeding habits influence forest succession and the plants of the forest floor. Large carnivores also eat midsized carnivores (their competition; or a tasty snack) and so influence songbird numbers. (Many so called mid size predators are nest predators of songbirds.)

The same is true in birds. Large raptors like goshawks eat crows (a nest robber, also on the increase since shooting of crows has been regulated) as well as rabbits and squirrels. Some great horned owls specialize in crows, which roost communally. Thus one sees flocks of crows roosting at night in the bright lights near malls or superhighways. Smaller raptors eat jays (another nest predator) as well birds the size of starlings and waxwings and also smaller ones like indigo buntings, house wrens and English sparrows.

North Americans are unlikely to live with mountain lions or wolves, despite the fact that deer, which are involved in 1.5 million car accidents yearly in North America, kill many more people than either. (Mountain lions will stalk and kill people but wolves, at least in North America, avoid them.) From a purely utilitarian point of view, we would be better off if mountain lions were abundant enough to control deer numbers and so reduce the number of people killed in collisions with deer (about 225 annually), even if the lions killed 10-20 people a year.

But the emotional difference between dying from a collision with a long legged herbivore that dashes into the road and from being stalked by a large cat that pounces on you from behind, breaks your neck, opens your chest and eats your heart and lungs, is of course considerable.

North Americans may manage to live with coyotes (many millions of Los Angelenos already do), which kill feral (and pet) cats, a major predator of songbirds (and keep many house cats, terrified, indoors). Coyotes have a major influence on songbird populations in Californian canyons: where there are coyotes there are songbirds, where not, not. Coyotes probably have some influence on deer populations through capturing fawns. (They may have more as, in the absence of the wolf, some populations evolve into a larger animal, better able to deal with larger prey.) Coyotes also eat chipmunks and white footed mice, a carrier of Lyme disease.

All this brings us to the suburbs, the modern barnyard, where dogs, cats and cars replace cattle, pigs and chickens: the home of modern people.

In dry climate suburbs are oases of damp. Screech owls are more abundant in Texas suburbs with their sprinkled lawns, and abundant insect life (a major part of the owl’s diet), than out in the dry countryside. (How long the sprinkling will last is another matter.) Many people feed songbirds, attracting at the same time raccoons, Norway rats, skunks, coyotes, crows, bears, red squirrels, chipmunks, white footed mice and other animals, whose presence they often come to regard as a problem. So suburban homes are equipped with pellet guns.

There are two problems. The first is deciding which animals we want to live with; the second is managing the habitat so as to provide a more complete compliment of species and so help control animals like crows, jays, opossums, English sparrows, feral cats and perhaps infections like Lyme disease. (The more species for the Ixodes ticks to bite, the less their level of infection—most animals are not competent carriers of the disease.)

Large undeveloped areas help. Not building the suburb but rebuilding the city to be more livable with trees, parks and public transportation, and still holding more people, helps the most. Deer may retreat to the wooded parts of cemeteries or golf courses during the day. Foxes, skunks and raccoons will make do with little cover, living under porches and becoming mostly nocturnal. More bears in Nevada live in Las Vegas than in the countryside. The city bears grow larger and have more young (on abundant dumpster food); but die more frequently in automobile accidents.

Keeping bears out of Las Vegas thus means bear proof dumpsters, and probably hunting; while keeping mountain lions out of western suburbs means keeping out deer, and probably shooting lions.

But we can deal with coyotes, as we do with (much more dangerous) pet dogs. Thus the undeveloped areas in the suburbs, ideally near watercourses. Coyotes need a retreat, as do great horned owls, barred owls and goshawks. Goshawks prefer a substantial tree (though not as substantial as those favored by the long winged ospreys and eagles), owls like dense cover for resting and nesting (a clump of hemlocks in a larger wood). Some owls will use nest boxes and, like bluebirds or wood ducks, their number can probably be increased this way, with salutary effects on populations of small rodents (like white footed mice).

Resident Canada geese can be controlled partly by manipulating their landscape: letting the grass grow. Geese will avoid tall grass or other cover in which coyotes can hide, while large areas of freshly mowed grass are ideal for them: long vistas; and a new meal, every day. Actually the cycle of grass, goose poop, grass is a virtuous circle which intelligent landscape managers could use (and thus save their fertilizer expenses) by devising a machine to pick up the poop to pile and compost (or pulverize and scatter). Clever construction of golf courses or playing fields would help keep geese away from people and their sandals. Some tolerance is necessary in any situation with animals, as is some predation on the geese, young or old, by humans, egg eating foxes, neck snapping coyotes, owls, goshawks and eagles.

So I imagine suburbs as fingers of settlement in larger swaths of desert, prairie or forest; the people generally on higher ground, away from water, near the breezes. Trees shade suburban roads, deciduous trees shade the south side of houses, clumps of evergreens block northwest winds. Banks of solar collectors shade roofs, laundry decorates the yards. Water drains in open ditches with cattails, frogs, nesting wrens, and probably a few mosquitoes. Such drains also absorb runoff from streets and parking lots (some also covered with solar collectors). The open land near the houses has playing fields and places for dogs to run, while the land further away (or near damper habitat) is left alone, with a few trails for birdwatchers or budding naturalists. Dead trees in the woods are left standing. Fallen trees are left on the ground. Larger streams run through the suburbs as corridors of native habitat, thus further filtering (along with the open vegetated drains) the runoff water that reaches them. Ideally, the sewage effluent from the town, purged of toxins (or free of them, since none go down the drain) only add sufficient nutrients to the water to improve the fishery (as that notable one for brown trout in the Bow River that runs through Calgary, Alberta; the brown trout is not native to the Bow and is out competing the native cutthroat trout—the same story as with browns and brook trout in the East—but nothing’s perfect). This is a matter of the volume of nutrients and of the stream.


Of course most of the nutrients in the sewage belong back on nearby farmland, with which, like the urban center, the suburb is allied.