I’ve often heard comments in the past from people who wonder if certain birds are moving beyond their normal ranges. This is especially common in winter, when unusual birds are noticed at backyard bird feeding stations or local birding hotspots.
I’ve always been cautioned when answering such questions about bird movements. Seasoned birdwatchers and scientists have been careful to say that anecdotal observations of a seasonal rarity (or a reduction in numbers of a certain species in a certain area) won’t necessarily constitute a shift in population ranges, or an effect on the population as a whole.
However, the recent release of a study by the National Audubon Society definitively shows that no less than a whopping 177 species of North America’s birds have shifted their ranges northward, some by hundreds of miles.
“Birds and Climate Change: Ecological Disruption in Motion,” a briefing of Audubon’s analyses of North American bird movements in the face of global warming, published earlier this month, was an eye-opener, to say the least.
The findings are a result of detailed analysis of 40 years of a “citizen science” project known as the Christmas Bird Count. The report states this “carefully organized and compiled observations of tens of thousands of Citizen Scientists participating in Audubon’s annual Christmas Bird Count have grown to form the world’s long-est uninterrupted repository of bird population information.”
Having participated in CBCs in the past, it is gratifying for me to learn that enduring hours of frozen, painful fingers and toes, biting winter winds, and other adverse conditions has certainly not been in vain. It is encouraging — but worrying — that those efforts have been so crucial to understanding how climate change is affecting bird populations.
I can guess what some people may be thinking — that our habit of feeding birds could be a significant factor in the northward range shifts. In fact, people have voiced that concern to me in the past. While some ornithologists have speculated this could play a role in certain species’ movements, and the report is careful to state that “Audubon does not suggest that all the birds that moved north or inland did so in response to climate change,” this recent, overwhelming evidence cannot be explained by the mere presence of backyard bird feeding stations.
The report states northern range movement has been seen in land birds, seabirds, and woodland birds. For example, the red-breasted merganser — a fish-eating bird of inland lakes and open seas — has moved 317 miles farther north. And although this bird normally winters along the coast, it has increasingly been seen on large inland lakes that are not freezing over as they had been decades ago.
The purple finch, a bird which does at times visit backyard bird feeding stations, is known as an “irruptive” species. Some years it may winter in more southern latitudes, while in other years it may travel northward, following the production of conifer seed-cones. The report states that “as temperatures have increased in recent years, however, the birds have not gone as far south during their irruptions — resulting in overall northward movement of over 433 miles in the last 40 years.”
Audubon’s briefing report showed that average temperatures for the month of January “rose more than five degrees F. in the continental U.S. over the past 40 years,” and it goes on to detail the myriad effects of global warming on bird species and the environment — and ultimately, on us.
The report is also a call to more immediate and urgent action, setting forth recommendations on how to reduce global warming pollution, and includes this warning: “Whether seen in the movement of the birds, or the melting of ice caps, the evidence cannot be denied — ecological disruption is under way.”
For more information, go to National Audubon’s Web site at http://www.audubon.org/bird/bacc/index.html. The full report is available for download there. You can also find out how to become involved in Citizen Science projects such as the Christmas Bird Count at http://www.audubon.org/bird/citizen/index.html.
To find out more about how global warming can affect bird populations, and how certain ecosystems can counteract the effects of global warming, discover The Boreal Songbird Initiative at http://www.borealbirds.org/index.shtml.