Sunday, May 22, 2016

The birds that live among us

kw: book reviews, nonfiction, natural history, birds, suburbs

I remember as a child living near the shore of Lake Erie, the morning chorus of birdsong that woke me in the spring and early summer. I taped it once, and I wish I had kept the tape. There seemed so many birds of so many different kinds…

I may have inflated it in my memory over the years. Some of the places I have lived since, didn't seem to have such a variety of birds. South Dakota, for example, just has fewer species because it is South Dakota, not Alabama. But recently I have been paying attention when I am out in the early mornings. It may be that here in the Mid-Atlantic the number and variety of singing birds is much the same as what I remember from fifty years ago in Ohio. Now I find a book that explores the relationship between bird numbers and diversity as they relate to different levels of urbanization: Welcome to Subirdia: Sharing Our Neighborhoods with Wrens, Robins, Woodpeckers, and Other Wildlife, by John M. Marzluff. A portion of the page space is well spent upon illustrations by Jack DeLap, a gifted natural history illustrator.

In ten chapters the book explores the relationship that different bird species have with our "built landscape". Chapters one through seven gradually paint this picture, primarily about species diversity:

  • In temperate regions, such as most of the United States and Europe, the number of different species is the least in inner cities; it is the greatest in suburbs; and it is somewhere in between in rural and forested areas.
  • In tropical regions, the trend is more linear: The greatest diversity is seen in the forests, the least in cities, intermediate levels are found in the suburbs.

In more absolute terms, the level of bird diversity is quite similar in suburban areas over most of the inhabited Earth. But in tropical forests the diversity is several times greater than in temperate forests. Also, worldwide, cities are bird-poor. In general, five very adaptable species are found wherever humans are: House Sparrows, European Starlings, Mallard Ducks, Canada Geese, and Rock Pigeons. Any place that didn't already have these species present, people brought them there, and they have flourished. So much so, that seeing large flocks of pigeons, frequently called "rats with wings", is a sure sign you are in an inner city.

To my observation, a city center is characterized by pigeons, sparrows, and starlings, while Canada geese and mallards favor the suburbs, which also have sparrows and starlings, but where pigeons are rarely seen. Of these five species, only the starlings and sparrows are truly abundant in forests, while meadows and farmlands tend to have very large flocks of starlings and substantial numbers of Canada geese.

Dr. Marzluff has led groups of students on numerous transects and species counts—these days the hip term is "bioblitz"—to confirm and quantify these effects. American suburbs provide two primary attributes compared to cities and temperate forests:

  • A greatly dissected forest-and-field landscape, with numerous mini-habitats that appeal to quite a variety of bird species. Other species that require large forested tracts avoid suburbs.
  • 55 million Americans spend $3 billion yearly on bird food and suet, and hundreds of millions more on bird feeders, birdhouses, and related equipment.

Several studies have shown that feeding wild birds causes a significant increase in the number of species, and the absolute numbers, of birds in an area. However, the suburbs also harbor a deadly enemy of small birds: millions of house cats, which kill at least two billion birds yearly in the U.S. I wonder, has backyard bird feeding increased the bird population sufficiently to offset the numbers taken by cats?

Of course, not all birds like birdseed or suet. Nor do they like the broken-up landscape of a suburb. Such bird species are "avoiders", and are rarely or never found in suburbs. The "adapters" seem to be tolerant and are about equally abundant in suburban yards and forests, while "exploiters" are more frequently found in the suburbs than elsewhere. But not all suburbs are of equal quality from a bird's perspective.

A friend of ours just bought a newly built home in a 55-Plus community. We saw the place when he asked us to accompany him to inspect it before signing the deed. The whole community is green grass and houses, and all the grass, to my semi-trained eye, is a single species of fescue. There are a few trees planted around the "community building" and other shared facilities. Otherwise, the entire multi-acre property is a green desert to all birds except American robins and starlings, which eat earthworms and yard insects. Fortunately, there are indeed earthworms in this development. I do hope many of the new homeowners will plant multitudes of shrubs and trees and flower beds; then springtime mornings will resound with something more than the robin's "Cheerio" calls.

My neighborhood was developed 60 years ago, and includes a substantial chunk of forest. Every yard has large trees, shrub plantings, flower beds, and various amounts of lawn grass. Off the top of my head, I recall that we frequently see or hear robins, starlings, several kinds of sparrow, chickadees, cardinals, goldfinches, catbirds, mockingbirds, mourning doves, swallows, and tanagers. Less frequently we see a couple kinds of woodpecker, geese (overhead; none have ever landed in our yard), vultures (frequent roadkill squirrels), red-tailed hawks, crows, jays, and orioles. I suspect if I recorded the morning chorus and teased out all the bird calls, there'd be a few more that I haven't yet identified. I am only the most casual of bird watchers.

Chapters 8-10 are more of a call to action. To favor birds in our neighborhoods, we need to foster a greater variety of native shrubs and trees (Azaleas are pretty but don't have much to interest a bird), and grow plants that also favor the birds' favorite insects. Butterfly bush brings adult butterflies, but a variety of spices and herbs are food for many of their caterpillars. A little lawn grass is good, but most yards could do better with less (and you'd spend less for lawnmower fuel!).

Cities can do more also. Every urban area has abandoned and unused land. Some of this can be deliberately planted to favor wildlife. Several instances are described of cities that deliberately increased their "emerald necklace", leading to a more pleasant city for all their residents; the familiar "rails to trails" initiatives are a great example.

As long as Earth's human population numbers in the billions, we will have cities and suburbs. The urban population will most likely double in another generation, even if total population growth slows. So will suburban population, meaning the area occupied by "single family homes" and townhomes and small-scale condo/apartment developments will double in area. With a little forethought, this can benefit wildlife overall, rather than decimate it.

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