Sunday, March 14, 2010

Predicting the State of the Birds

Last week, the Interior Department, Audubon, and a coalition of other conservation-minded organizations announced the 2010 State of the Birds report. (Oddly, the report was released late on a Thursday; usually the end of the week is reserved for news that agencies would prefer people not notice, like bank failures.) This year's report tries to predict how birds might respond to climate change. It suggests conservation actions to mitigate those responses and reduce stress as the climate continues to warm.

Relative vulnerability of U.S. birds by habitat

The report divides birds into groups based on broad habitat types or location. Since this was produced in part by the Interior Department, the report includes all birds found in the United States and its territories, including islands in the Pacific and West Indies. Each bird species was assessed on five traits and rated as high, medium, or low vulnerability based on that assessment. Here, briefly are some of the report's predictions.
  • Oceanic birds will face changes in prey distribution, which will affect the viability of breeding colonies. In addition, sea level rise may threaten low-lying colonies.
  • Coastal birds, which use beaches and salt marshes, face threats from sea-level rise, both from permanent inundation of some low-lying areas and from increased flooding and erosion.
  • Arctic and alpine species are handled together because they face the similar problem of having few options for moving to more suitable areas as their current habitat warms. Arctic birds are often long-distance migrants, so they face climate-related changes all along their migration routes. In the Arctic, melting permafrost could release additional toxins and allow woody plants to encroach on tundra habitat.
  • Island birds (both Pacific and Caribbean) are particularly vulnerable if they are endemic to an island, as is true of 42 Hawaiian bird species. A warming climate could create significant changes in precipitation; this would affect the vegetation and insect life that birds depend on.
  • Aridlands will become warmer and drier, which will fundamentally change the vegetation structure in many areas. As precipitation decreases, riparian habitats will shrink, along the bird populations that depend on them. Some species may get a boost as arid habitats are expected to expand to the north and east.
  • If temperatures increase without a corresponding increase in precipitation, wetlands could shrink considerably from evaporation and loss of input. Mountainous wetlands and the prairie pothole region are particularly vulnerable. 
  • Grasslands are expected to become drier, and continuing increases in atmospheric carbon dioxide could encourage woody plants to encroach on grassland habitat. The vulnerable grassland birds are those that are less likely to move in the face of changing habitats, such as grouse. 
  • Forest types are likely to shift northward; oak-hickory and oak-pine forests will expand considerably, while other types will contract within the United States. The boreal forest will shrink somewhat as its southern border moves north. Most forest birds are not at high risk because they reproduce quickly, but species that rely on a single forest type will face challenges.
The predictions discussed in this year's report are not for changes far off in the future. In some cases, they are happening already. Bird species are known to be shifting their winter ranges northward, based on Christmas Bird Count data.

For more details, including recommended conservation measures, see the full report.

Mitigation is going to become increasingly important as the climate continues to warm. At this point it seems unlikely that we will see effective action from the U.S. Congress on climate change. Even if the EPA is successful in imposing greenhouse gas restrictions, its restrictions may not reduce emissions quickly enough. So we are likely looking at some pretty dramatic changes over the next few decades, and long-term conservation plans will need to account for that.