Sunday, November 9, 2008

The Birdist: "As Refuted By David Sibley!"

Master birder/fieldguidist/artist David Sibley has recently picked up the discussion of "how many rare birds to we miss?" on his personal blog, Sibley Guides Notebook.  Since I had interviewed John of A DC Birding Blog about that very topic back in March, I left a comment with the link in Sibley's comments.  On Thursday Mr. Sibley posted his own answer to the "how many do we miss?" question, suggesting that the number is somewhere around 3 to 10 percent.

And you know what?  He's right.  What made me think so?  It wasn't that blog post, but it was an example Mr. Sibley used: the search for the European Golden-plover.  

Mr. Sibley began the discussion of finding rare birds by linking to a video of a moonwalking bear.  Well, the search for the EUGP in Scarborough Marsh was pretty much exactly like the classic sniper training scene (careful, there's a swear word in there) from A Clear and Present Danger: a bunch of guys with binoculars staring into a field, failing to locate something they know is there.  

Standing at Seavey's Landing that morning, I realized how truly difficult it is to find an extralimital bird.  Here, completely surrounding this one square mile of marsh, were probably 50 of the best birders in New England, all with their scopes trained.  For hours.  No bird.  

If 50 experts with scopes can't find one little bird in a field, what chance does one expert have?  What about one non-expert?  What is the EUGP had landed in any of the many less-birded or less-accessible areas of Scarborough Marsh?  The odds become miniscule.  I mean, there are only a handful of birders in Maine good enough to suspect that the bird was anything but an American Golden-plover (I'm not one of them, but thank goodness that Robby Lambert is), and that's if they were lucky enough to get a good look at it to start with.  

Secondly, I came to a separate realization about finding rare birds while looking for the EUGP.  After hours of sitting on the outskirts of the marsh, waiting fruitlessly for the bird to appear, some Mass. birders and I decided to start walking through the marsh, hoping to locate the bird closer to where it had been last seen.  During our walk we repeatedly kicked up birds that no one else had been seeing, including American Bittern, Snipe and Pectoral Sandpipers.  All these birds, like the EUGP, were hunkered down in the grass, unseen by the mighty 50 and their powerful scopes.

Scarborough Marsh is probably the most heavily birded area in Maine (except for maybe Evergreen Cemetery in early May), and yet it took a mighty effort to refind a single extralimital bird there.  Mr. Sibley is right, the actual find-rate for extralimital birds must be much less than my estimate of 1/3.  Well, unless you've got Robby Lambert on your side...


Brazilian girl on NYC said...

Fascinating. Reads like a movie. So to be clear: you/Sibley estimated that 3-10% of extralimital birds were likely found by birders (not missed). Wonder what percentage are found now in 2021.

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