Wednesday, June 8, 2011

379. Songbirds Face a Danger of Early Arctic Spring

American tree sparrow.
American Tree Sparrow

By Natalie Boelman, The New York Times, June 7, 2011
Many of the songbirds that spend winters in our backyards spend the spring and summer months breeding in the Alaskan Arctic.  For example, those of you living in New York State have probably observed dark-eyed juncos, American tree sparrows and American robins at your bird feeders. Populations of all three of these species travel up to 3,000 miles to the tundra every spring to find a mate and start a family, and then they take the whole journey all over again, in reverse, just two short months later.  Why travel such great distances?  Because relative to more southern ecosystems, the Arctic tundra boasts an abundance of high-quality food resources, and is home to relatively few predators and parasites.  Despite the distance from overwintering grounds, these attributes make the tundra particularly well suited to rearing chicks and fledglings. However, we suspect that this might be changing.
The Arctic is notorious for having huge variations in the timing of snowmelt from one year to the next. But over the past couple of decades, an underlying signal of earlier snowmelt has emerged as one of the major effects of Arctic warming. We already know that tundra plant growth begins earlier in years when the snow melts early, and we’re pretty sure we’ll find that insect emergence occurs earlier

For these and other reasons, we hypothesize that as Arctic warming continues, consistently early starts to spring are likely to affect migratory songbird communities, because the birds always arrive on the tundra at the same time every year, ready to breed and needing to eat, regardless of snowcover conditions.  For example, at the Toolik Field Station where we’re conducting our fieldwork, the main influx of songbirds consistently occurs between May 17 and 30.  The reason for such punctuality in tundra arrival time is that these birds are cued to leave our backyards every spring by changes in day length.  Because the timing of this “light cue” is not changing in relation to recent climate warming, the birds are very likely to continue to arrive at Toolik at the same time, despite an earlier onset spring in the Arctic.
If spring snowmelt begins earlier as the climate continues to warm, will arriving songbirds miss an important pulse of early-season plant and insect food resources?  Will earlier onset of plant growth and insect emergence alter the timing of various food resources throughout the songbird breeding season?
Here’s an everyday analogy that I heard a colleague of mine, Eric Post, use in an NPR radio interview last year, in which he was talking about the effects of early snowmelt on Arctic caribou. Imagine that you go to the cafeteria for lunch every day from noon to 1 p.m. One day the cafeteria decides to start opening at 11 a.m. and closing at noon, without letting you know. When you show up at noon, you might be lucky enough to score some leftovers, but it’s also possible that you’ll completely miss out on lunch.
Will the songbirds be able to adapt to these changes in the timing of food resources? Or will so-called trophic mismatches develop that alter their reproductive success?  Will the assemblage of songbird species we see hanging out at our backyard feeders today be different as a result of Arctic warming? These are some of the questions we are trying to answer.
Keeping Track of It All
To answer these types of questions, we need to keep track of a large suite of conditions and happenings on the tundra, including weather, snowmelt, plant growth, berry and seed production, insect abundances, and of course a variety of variables associated with the birds themselves.  We have to monitor all of this on a daily to weekly basis, at each of our four field sites, from early May through late July. As you can imagine, this sort of undertaking takes a very dedicated and sizable field team, and we have just that.  At this point in the season, there are 11 of us (including the three lead scientists, undergraduate and graduate students, a postdoc, a field assistant and even an expert volunteer helper) roaming the tundra.We refer to ourselves as Team Bird, and we have team T-shirts with our logo,  a bird singing into a microphone, featured front and center.  Why a bird singing into a microphone?  Because we’ve set up a “bioacoustic recording network” on the tundra that records songbird vocal activity throughout each breeding season — more on this in a future blog post.

Natalie Boelman, an ecosystem ecologist at the Lamont-Doherty Earth Observatory at Columbia University, writes from the North Slope of Alaska, where she is studying the effects of climate change on the interactions among plants, insects and migratory songbirds.

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