Backyard Birds Spreading as Climate Changes

Global Science Report is a feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

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In a recent Global Science Report, we posted some good news coming out of California’s Sierra Nevada, where climate change (from whatever cause), has been partially responsible for a greening of the organo state. Technically, the biomass in the montane forests has been on the increase over the past several decades.

Turns out climate change is for the birds, too. Yes, little Eastern Bluebirds (which almost went extinct because of habitat damage)—raising their young in cute houses, awakening us with their melodious songs, providing free cat food, and selectively messing only on my car. What’s not to like? And who wouldn’t like more birds? And if you live in the Eastern United States, there is a climate-related increase in cat purring because global (actually, local/regional) warming is increasing the range of songbirds.

A new study appearing in the journal Global Change Biology, authored by Karine Princé and Benjamin Zuckerberg from the University of Wisconsin-Madison’s Department of Forest and Wildlife Ecology, finds that:

[A] shifting winter climate has provided an opportunity for smaller, southerly distributed species to colonize new regions and promote the formation of unique winter bird assemblages throughout eastern North America.

The operative word here is “colonize.” In other words, they are spreading out from their home range, not moving north in lockstep.

Linking observations from the amateur bird surveys with temperature data from nearby locations, the authors track how the birds are responding to changing winter conditions. During the period 1990–2011, Princé and Zuckerberg find that the average environmental temperature characteristic of the observed bird assemblages indicate a “northward shift in the community composition of wintering birds” of about 93 miles during the period 1990-2011. Most of that shift is the result of warm-weather adapted species with short migratory paths, such as the Chipping Sparrow and the Carolina Wren, which are both expanding their ranges northward as well as increasing their populations within already established ranges. The authors tell us:

We found that the stronger positive … trends in southerly latitudes were driven by warm adapted birds increasing in their local abundance and regional occurrence... Despite diminished trends … in the more northerly latitudes, these trends were also driven by southerly species expanding their range (e.g., Carolina Wren and Eastern Bluebird) as opposed to cold adapted birds becoming locally extirpated and shifting northward.

This is pretty good news. Biodiversity—which everyone seems to like—is on the rise.

The authors sagely point out that “[c]limate change should not be viewed as the sole driver of changes in winter bird communities in eastern North America,” and note that changing landscapes, changing backyard bird feeding habits, changes in the observing network, etc., may play some role in the results. They also note that the changing community structure of the bird species may act to alter the “biotic interactions” within the winter bird communities, implying that there may ultimately be winner and losers. (A “W” goes to the cats.)

The data show that bird species are pretty much doing what rational climate optimists (h/t to Matt Ridley) expected all along, that is, adapting to changing climate conditions—and not only adapting, but thriving. And cats are purring with approval.

Reference:

Princé, K. and B. Zuckerberg. 2014. "Climate Change in Our Backyards: The Reshuffling of North America’s Winter Bird Communities." Global Change Biology, doi:10.1111/gcb.12740.

Ridley, M. 2010.  The Rational Optimist: How Prosperity Evolves. New York: Harper.