For the Birds – Earth Day

Wednesday is Earth Day. In today’s column, I will review a couple of major studies that have examined the impact of humans on bird populations. Both of these studies are based on citizen-science projects. Many of you will have contributed to the databases.

National Audubon scientists recently released the results of their study of the past 40 years of Audubon’s Christmas Bird Counts. The scientists analyzed the population changes of 305 bird species that occur widely in the winter in North America.

Of this total, 177 species have shifted their range northward. This northward shift is consistent with global warming. The average shift northward over the past 40 years is 35 miles for all 305 species, including those that do not show northward movements.

Of course, averages can mask more dramatic changes for some species. Boreal Chickadee, Purple Finch and Pine Siskin have retreated dramatically into Canada. The center of the ranges of these species has moved 211, 313 and 246 miles northward since 1968.

Species that rely on open water show pronounced shifts in their ranges as well. American Black Duck, Ring-necked Duck and Red-breasted Merganser show a northward shift of their ranges by 150 to 250 miles. These birds are able to winter further north because more open water is available in northern states and Canada.

Consider the increase in average number of the following species in Maine between 1968 and 2008: Mourning Dove (22.4 times increase), Red-bellied Woodpecker (5.5 times), Carolina Wren (5.0 times), Hermit Thrush (9.8 times) and White-throated Sparrow (2.8 times).

What’s the big deal you may ask? Don’t the birds just shift their ranges northward with no overall change in abundance?

Actually, this expansion of ranges toward the poles should give great concern. Consider a typical map of the world using a Mercator projection. On such a map, Greenland looks to be about the same size as Africa. In fact, Africa has 14 times the area of Greenland. A Mercator map distorts the area of land near the poles.

Instead, think about a globe of the earth with lines of longitude on it. Follow two adjacent lines of longitude from the equator to the North Pole, noting how the lines get closer and closer as you move from the equator.

By forcing birds northward, we are funneling them into smaller and smaller areas. Sooner or later, the birds will run out of habitat.

A second major report, The State of the Birds: United States of America, was recently published by a partnership of a dozen government and non-government organizations, including the Cornell Lab of Ornithology, the National Audubon Society and the U.S. Fish and Wildlife Service.

The report used three sources of data on bird population changes: the Christmas Bird Count, the Breeding Bird Survey and the Waterfowl Breeding Population and Habitat Survey.

The report is a balanced report, noting species that are declining and increasing. Environmental threats are thoroughly discussed and reasons for hope are covered as well. The report is mainly organized by general habitat, such as grasslands, arid lands, forests and wetlands.

Let’s consider forests as a representative habitat. The report tells us that North American forests harbor more than 300 species of breeding birds. Although some species are doing well, fully a third of these bird species are declining. The threats are familiar ones: unplanned, urban sprawl; unsustainable logging practices; intense wildfires caused by decades of fire suppression; impact of tree insects and tree diseases driven in part by climate change.

Examining eastern forests, the authors found that 25 species found exclusively in forests have declined in abundance by 25% in the past 40 years. Species of particular concern from eastern forests are Eastern Wood-Pewee, Wood Thrush, Blackpoll Warbler, Cape May Warbler, Pine Siskin, Evening Grosbeak and White-winged Crossbill.

To halt the declines, the authors suggest better planning of human development, green logging practices and doing all we can to slow the rate of carbon dioxide emissions to at least slow down the rate of global warming.

Space does not permit consideration of all the habitats covered in this thoughtful report. Copies are available for download at http://www.stateofthebirds.org/ I encourage you to read the document ; it will be well worth your time.

Finally, here are some suggestions for ways we can combat climate change. Visit http://www.birdsandclimate.org to sign the petition urging lawmakers to take steps to slow global warming. Determine your energy profile and carbon footprint. A number of carbon footprint calculators are available on-line. Become a locavore; buy locally grown produce and other food as often as you can. Plant more trees. Happy Earth Day!

[Originally published on April 18, 2009]