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    I’ve got it narrowed down to two…

    “I can’t decide; I saw it well enough, but I’m not sure which one it was!” This is a common identification challenge for various pairs of common birds. It is easy to narrow it down to two species, but taking that last step becomes much more difficult. In eastern North America, I think that one of the best examples of this conundrum is Downy vs. Hairy Woodpecker. These are both rather common birds that are seen often, but it can be hard to make that final decision: Was the bill long enough? How big was it? This is one of those cases where a simple psychological rule can be applied: If I’m questioning which one it is, it is probably a Downy. When an actual Hairy shows up, there is usually not much question as to its identity. The bill seems clearly longer, the bird seems bulkier, has more obvious “shoulders”, and everything adds up to Hairy Woodpecker. When you are confronted with a Hairy Woodpecker, you know what it is. When you are confronted with a Downy Woodpecker, it is easy to question yourself and try to trick your mind into believing the bill seemed a little long or it wasn’t small enough. Deliberation should encourage strong consideration of the default choice. In this case, Downy.

    Another pair that often causes confusion is Greater vs. Lesser Yellowlegs. In this case, I think that the default should be Lesser Yellowlegs. Again, when confronted with a Greater Yellowlegs, the larger size and longer, upturned bill make it obvious. If you are asking yourself which one it is, it is probably a Lesser.


    Yellowlegs88

    A yellowlegs, but which one? Nothing about the bill “jumps out” at me, so I’ll call it a Lesser.

    I can certainly think of a few pairs of species where I don’t recommend this approach: Cooper’s vs. Sharp-shinned Hawk and Short-billed vs. Long-billed Dowitcher come to mind. With these pairs, there is no default species (except expectations due to distribution or migration patterns). Each time these species are encountered, they must be carefully considered, and I don’t expect anything to be exceptionally obvious on one or the other.

    I’d be interested to hear of other examples where this psychological trick (“If it doesn’t jump out at you, it must be the default species of the pair”) can be used. Any suggestions?

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    Blake Mathys

    Blake Mathys

    Blake Mathys completed his Ph.D. at Rutgers in 2010, studying evolution of birds introduced to islands. His field work was in Bermuda, Puerto Rico, Hawaii, and Trinidad, and was complemented by museum research. Prior to graduate school, he worked with Cape Sable Seaside Sparrows in Everglades National Park, as a hawk counter in Washington State, on the Farallon Islands studying Northern Elephant Seals for PRBO Conservation Science, and sampling fish for the Ohio EPA. Blake and his wife Dimitria recently moved to Ohio, where he is an Assistant Professor of Environmental Science at Ohio Dominican University in Columbus. Aside from birds, he maintains a fascination with salamanders, mammals, and anything else with a backbone.
    Blake Mathys

    Latest posts by Blake Mathys (see all)

    • Thomas Bayes

      In these cases, wouldn’t it just be better to leave it at “one of the two”? Deciding on one or the other suggests a level of certainty that just isn’t real. We live in an uncertain world, better to accept it (or even quantify it) than to live in denial.

    • http://profile.typepad.com/blakemathys Blake Mathys

      My hope with this post was to suggest that you can be reasonably certain, because you can use uncertainty as a “field mark”. When identifying birds in the field, we must accept that we won’t always be right (and genetic testing would probably reveal many stealth hybrid individuals that look like stereotypical examples of normal species). My idea for this post is to suggest a further identification clue that will help lead us to the correct identity. If used with caution and concern, I believe this approach is appropriate for many identification challenges.

    • William von Herff

      I think another example of the ” uncertainty as a field mark” would be common raven and american crow. If you see a raven, its larger size is obvious. But with a crow, you may start thinking, ” Is that big enough to be a raven?”.

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