Climate Change and Winter Birds

Yesterday the National Audubon Society released a new "State of the Birds" report on Birds and Climate Change. The results are sobering. During the past four decades (1966-2005), the winter ranges of the 305 bird species observed during Christmas Bird Counts have shifted northward by an average of 35 miles. Over 60 species have moved more than 100 miles north.

Here are a few examples of birds from the report:

• Purple Finches have not traveled as far south during winter irruptions and are spending winters 433 miles north of their previous range.
• Marbled Murrelet faces the dual threat of climate change and loss of old-growth habitat in the Pacific Northwest.
• Red-breasted Mergansers now winter in the Great Lakes and upper Midwest in increasing numbers, representing a northward shift of 317 miles.
• Pine Siskins are wintering 288 miles farther north despite the thistle offerings of hopeful backyard birdwatchers.
• Boreal Chickadees (pictured), having moved 279 miles north, are becoming less common along the northern border of the United States.
• Eastern and Western Meadowlarks have not moved north; the population of Eastern Meadowlarks has fallen 72% during the past four decades.
  

These range shifts indicate that major changes are taking place in North American ecosystems. While we should not dismiss other potential influences like habitat destruction in the lower 48 states or wider availability of bird feeding stations in northern latitudes, there is one major transition at work. During the past four decades, the average January temperature in the lower 48 states has risen about 5°F, from a little over 28°F to about 34°F.

Warmer winter temperatures can mean many things. Water in lakes and rivers is less likely to be frozen, meaning more opportunity for waterfowl, herons, and kingfishers to forage. Reduced snow cover makes it easier for ground-foraging birds to find food, even without handouts from humans. For insectivores, warmer temperatures mean that insects and other invertebrates will be available for more days per year. All of those things give birds the ability to survive winter farther north.

Some species may see population increases, at least in the short term, as a result of warming. However, many bird species face a dismal future. Arctic species – birds of the tundra and of northern ice floes – will gradually see their breeding habitats disappear. (Goodbye, Ivory Gull!) Coastal birds may see their habitats disappear under rising seas, and even if replacement habitats are created, their reliance on food from the ocean makes their future status uncertain. Grassland birds in the United States, unlike the woodland counterparts, may be unable to shift their ranges to cope with warming. Much of the former grassland habitat in the United States has either been replaced by subdivisions or hopelessly degraded by industrial agriculture.

As the report (pdf) states, "failure to prevent the worst impacts of global warming would undermine much of the conservation work that Audubon has accomplished for more than a century." The same could be said of other environmental organizations, federal and state governments, and any individuals who have worked on behalf of bird populations. We need action on climate change, and we need it now.

Audubon California and Audubon Washington have issued reports on birds and climate change within their own states.