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Where Are the ECDs?

Check out the eBird map for the Eurasian Collared-Dove’s distribution, and you’ll see a mystery. Since the early 1980s, the dove has rapidly colonized almost all of the western U.S. and parts of southwestern Canada. Now it has begun to appear in small numbers as far north as southern Alaska and adjacent British Columbia. Yet in the east, although spotty occurrences now extend into New England, a solid expansion along the Atlantic coast has not occurred beyond North Carolina.

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photo by Ali Iyoob

From the dove’s viewpoint, what’s wrong with the mid-Atlantic and New England states? I was hoping a recent paper in Ibis, the British Ornithologists’ Union journal, would provide an answer or at least a convincing speculation. Alas, it does not—but it does succeed in making the mystery more interesting.

Ikuko Fujisaki, Elise V. Pearlstine, and Frank J Mazzotti at the University of Florida compiled 2007 data for the Eurasian Collared-Dove from 1,716 Breeding Bird Survey routes in the continental U.S. The authors used a variety of statistical methods to determine whether presence/absence and relative abundance of the species is associated with environmental factors that might explain the pattern of range expansion.

They found patterns similar to those that marked the dove’s rapid spread westward and northwestward from southern Asia through North Africa and all of Europe within half a century. Among results of the analysis:

• Small numbers of Eurasian Collared-Doves “jump” to isolated areas ahead of the main wave of colonization, and then uncolonized areas are filled as the new local populations grow. These isolated appearances have sometimes been thought to represent releases or escapes, but the jumps are so frequent and widespread that a natural process seems more plausible.

• Favored habitats tend to be human-altered landscapes including urban and suburban areas, as well as rural areas including farm fields and pastures with a mix of shrub and tree cover.

• Abundance is usually greater in warm climates, although the species also lives in relatively cool regions such as the northwestern U.S. and southern Alaska (and in the Old World, as far north as western Siberia).

• The dove is generally more abundant in coastal regions than inland.  

Those results are not particularly surprising, but the authors call attention to the unsolved mystery: Dispersal and population increases have been much greater westward along the Gulf coast than northward along the Atlantic coast.

(Interestingly, there is a similarity between the dove’s pattern of expansion and the Great-tailed Grackle’s widespread advance westward and northwestward from its origin in Texas. As a Birding article(.pdf) reported in June 2004, the grackle’s advance has also been associated with human activities, and this species has shown no interest in expanding eastward or northeastward.)

If the dove’s colonization along the Atlantic has stalled, what undetermined factor(s) might be limiting its further expansion in the east? Let’s hear speculations from ABA blog readers.

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Paul Hess

Paul Hess

Paul Hess, the Birding "News and Notes" Department Editor, started watching birds at age 7 in Los Angeles. Now a retired newspaper editor in Pennsylvania, he formerly chaired the Pennsylvania Ornithological Records Committee, has contributed many articles to the journal Pennsylvania Birds, writes an ornithological news column for the Pennsylvania Society for Ornithology newsletter, edits the Three Rivers Birding Club newsletter in Pittsburgh, and has coauthored several National Geographic books on birds. Paul has received prominent awards for outstanding contributions to Pennsylvania ornithology and for bird conservation efforts in the state.
Paul Hess

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  • Matt Pelikan

    As a New England birder who has followed the expansion of this species pretty closely, I’m also curious about the odd pattern ECDs have shown. But the pattern is surprising only if we assume their urge to move is the same in all directions. Is it possible the species (or the source population in Florida) has a propensity to move northwest? No idea what the mechanism might be, but I’ve read studies suggesting that some nocturnal migrants essentially make sure the setting sun is to the right as they take off. Could ECDs, for example, tend to take off on journeys in the morning, with the sun behind them, and follow the resulting bearing?

  • Well, here in Brooklyn, we’re waiting… the Cooper’s hawks are hungry in this snow.

  • T. Ludwick

    The ECDO’s expansion in Europe and Asia displayed precisely the same pattern. They generally dispersed to the northwest from India and Pakistan ending up in Scotland. Many of the birds found in China to the east of the source population were purposefully introduced.

  • Here in northern Illinois, especially in the Chicago area, we’ve been wondering the same thing. In my neighborhood, at least, I think I’ve figured it out.

    I have a picture from January of 2008 of the roof of my garage covered with about 40 sunning ECDs. They were in or around the neighborhood constantly, and it was quite easy to find them and their nests. They are big, showy and compared to MODO, slow moving.

    Enter the Cooper’s Hawks. Coops have also become common in my neighborhood also … and now the Eurasian Collared Doves are gone. Not just less common, but GONE.

    I’m not sure what the Coop situation is out west, but the small towns and quiet neighborhoods that ECDs tend to favor out east are just chunky-jam full of Cooper’s Hawks.

  • Tim

    Now that is fascinating. I had thought it was likely a response to climate and habitat patterns – the Atlantic coast has a very different seasonal weather pettern than the Pacific coast, and the two regions have very diffferent habitats as well – but that wouldn’t explain a similar pattern in Eurasia.

  • Andy Paulios

    Did the study authors use
    Cooper’s hawk relative abundance
    from the BBS as a covariate?
    I’m skeptical that this is the answer.

  • Interesting thoughts, Greg and Andy.

    I just checked to paper again. No, the authors did not include predation by Cooper’s (or any other predator) in their analysis.

    I can say, though, that BBS data would not have helped. Samples are too small for analysis even on the continental level. See:

    http://www.mbr-pwrc.usgs.gov/cgi-bin/atlasa09.pl?03330&1&09

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