As an amateur ornithologist I look forward every year to the changing of the guard in migratory bird populations. After a long cold winter, the springtime arrival of robins is always a welcome sight, a harbinger of warmer days ahead. And when their numbers dwindle in the fall, I know winter is on the way.
This time was different: the robins never left. At first I hardly noticed, but when in December I began to see flocks of thirty to forty of the red-breasted birds lining roof eaves and crowding bare tree limbs, I knew something unusual was going on.
For the last few years, when the juniper berries on the bushes in front of my Carbondale home ripen in January, scads of cedar waxwings arrive for the harvest. This year they were replaced by robins. I didn’t even know robins ate berries as I was so used to observing their comical worm wrangling on grassy lawns. But there they were, jostling for position on the juniper branches like women at a Macy’s one-day sale. The berry crop, which used to take the waxwings a month to devour, was gobbled up by the larger robins in half that time.
It seems the birds knew beforehand what we in the Roaring Fork valley have been observing recently. No one who’s lived here for the past ten years can deny that this has been a strange weather year; the dwindling of driveway ice even in shady areas, bare ground visible for weeks on end, nighttime temps in the mid-thirties and rain! It’s almost enough to convince diehard creationists that global warming is for real. In fact, there is data that supports the idea that climate change is responsible for the wintering over of our robins.
“Of 305 species tracked by the Audubon Society, more than half are spending the winter about 35 miles farther north than they did 40 years ago,” reveals an Audubon study released on February 10th. The four decade long study is based on data collected during the Audubon Society’s annual bird count. During the period of study, the average January temperature in the U.S. climbed by about 5 degrees.
According to researchers, “The changes in migration coincide with variations in temperature over time, suggesting that many birds are responding to climate change by moving into new ranges.” Confirming my observations, the report stated: “There are fewer American robins and cedar waxwings in Texas than before, but their populations are growing in spots to the north.”
Birdwatchers like myself are rightfully concerned about the shift in bird migration. Senior researcher at the UK’s Royal Society for the Protection of Birds Paul Donald says, “Many long-distance migrant birds in Europe are suffering long-term population declines, and these results suggest an additional danger posed to them by climate change.”
For the past decade, biologists have been exploring the possibility that warmer winters could increase the survival of birds that live in an area year-round, giving returning migratory birds in the spring more competition for food and nest sites. That could potentially cause a decrease in the total number of migratory birds and even affect the survival of certain species, giving us front row seats at the enactment of Darwin’s theory of adaptation.
For my part, I’ll be paying closer attention to the correlation between bird migration and annual weather patterns as I continue to make amateur observations from my front porch, and report my findings to Audubon in the hope our nation’s new leaders will take note of the statistics.
After all, if Mother Nature is trying to tell us something, maybe we should respectfully listen.
Sources: “Visitors passing through: Audubon Society study bird migration shift to climate change,” Houston Chronicle, February 10, 2009. http://www.chron.com/disp/story.mpl/front/6255181.html
“Bird migration at mercy of weather patterns,” New Scientist, May 17, 2008. http://www.newscientist.com/article/mg19826563.500-bird-migration-at-mercy-of-weather-patterns.html “Climate Change Linked To Migratory Bird Decrease,” ScienceDaily, Mar. 26, 2003. http://www.sciencedaily.com/releases/2003/03/030326073630.htm